What continuous A rating should I choose for jump leads? - Page 1
Forum section: electronics / beginners

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 09:51:52 am
content: If connecting lifepo4 and starter in parallel, only for temporary to charge either one, I still don't get how I figure out the maximum continuous rating I should select for the cable of the jump leads?Continuous because if I want to keep them connected to drive charge into either starter or leisure, depending on which one depleted.I was told not to use the Ah but not told whattouse to decide.I will want to get an inline mega fuse of course for this but have to know cable size to pick first to choose what fuse holder to size the connectors to.Most of the leads on sale show only their peak current and not continuous rating. I have found a couple that show continuous but as above don't know which I should select!Theseare some of the heaviest I have found online and you can see they come either in 240A or 345A continuous. Should I go for 345A to be on the safer side and would that definitely cover it? 50mm2 cable then I would have to find a hefty inline fuse to manage that.I did find bigger rated ones for HGVsbut then more expensive again.Heresome rated at 600A continuous.I really have no idea of what will be 'enough' for this use case if one of the batteries is deeply depleted?

author: madires
author_rank: Super Contributor
timestamp: July 16, 2025, 10:02:48 am
content: The wire resistance and the maximum temperature determine the current rating. Rule of thumb: 0.1mm² for 1 A continuously.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 10:08:37 am
content: Quote from: madires on July 16, 2025, 10:02:48 amNot what I am asking. I know what the wire ratings are. I am asking what size I should choose for the situation listed above. The ratings are listed already. I am asking what ones I should pick.

author: madires
author_rank: Super Contributor
timestamp: July 16, 2025, 10:23:07 am
content: What is the recommended maximum charge current for both batteries? IIRC, for lead acid it's around C/4 or C/5.

author: Gyro
author_rank: Super Contributor
timestamp: July 16, 2025, 11:44:29 am
content: You've already covered this ground inhttps://www.eevblog.com/forum/beginners/ok-to-make-direct-connection-between-vehicle-and-leisure-battery-in-a-scrape/Covering old ground in a new thread loses context, wastes people's time and annoys them.

author: Simon
author_rank: Unknown
timestamp: July 16, 2025, 01:01:03 pm
content: Here we go again.......So are you asking for the cable size or the current the cable will carry between your unspecified batteries? even knowing the batteries the current depending on several other factors.Frankly given your abilities I would leave well alone. Batteries unlike power supplies store energy and can release it all in one go very fast.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 04:06:56 pm
content: Quote from: Simon on July 16, 2025, 01:01:03 pmI am asking what continuous current I should get for jumper cables if I wanted to link them in parallel in an emergency.The starterdatasheet.For the leisure batteryhereis the datasheet.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 04:08:35 pm
content: Quote from: Gyro on July 16, 2025, 11:44:29 amYes I had forgotten about that thread until after posting it.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 16, 2025, 04:13:05 pm
content: The alternator doesn't regulate current it only regulate the voltage. You wouldn't know how much the charging current is and it depends on the state of charge of the battery. Normally the charging current is high only for a very short time because the battery in a vehicle normally doesn't get discharged very much before it's charged.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 04:13:44 pm
content: Quote from: madires on July 16, 2025, 10:23:07 amLooking at the datasheets, for the starter 1/10th of rated current, so 7.2A. For the leisure battery 100A

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 04:16:00 pm
content: Quote from: BeBuLamar on July 16, 2025, 04:13:05 pmThe question is related for only in a situation if the alternator failed and the starter went down to almost totally flat so then I could put charge back in it from the solar panels.Vice versa, perhaps in winter I totally flattened the leisure one I would want to put some juice from the starter into the leisure battery, just enough to wake it up again because the dc-dc charger won't even work if the leisure battery is too flat, so would only be to bring it back to life again.I was told somewhere that if one or other is very discharged it could cause a surge in current once they are linked. The question is how much?

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 16, 2025, 05:36:20 pm
content: Quote from: electroniclearner820327 on July 16, 2025, 04:13:44 pmThat's what you should charge the battery at but you wouldn't know how much your alternator will charge your battery. Why don't you measure the current?

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 05:55:42 pm
content: Quote from: BeBuLamar on July 16, 2025, 05:36:20 pmThe scenario though is that the alternator would be broken if I was doing this which is why I would want to do it as the starter battery would have died.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 16, 2025, 06:31:33 pm
content: I don't understand how you want to do it? I thought you want to charge your LiFePo4 battery with the van alternator?

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 16, 2025, 06:39:44 pm
content: Quote from: BeBuLamar on July 16, 2025, 06:31:33 pmNope, not it at all.See reply #5 for previous discussion in depth but it is not complicated.One battery flat, other one charged. Link them in parallel with jumper cables to give the flat one some charge. Nothing to do with alternator or other charging device.The question is only what continuous amp rating should I choose for the wires give the technical sheet for each battery I provided above?

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 16, 2025, 07:18:04 pm
content: If the full one is full and the flat one is about 20 or 30% charged then I would expect the current to be very high. Perhaps 30A or more. You can measure it and see. The current is the full battery voltage - the flat battery voltage divided by the internal resistance of both battery together. Since the full and flat voltage can be about 2.8V different and the internal resistance of the batteries are very low the current would be very high.

author: IanB
author_rank: Super Contributor
timestamp: July 16, 2025, 07:40:47 pm
content: Quote from: electroniclearner820327 on July 16, 2025, 04:06:56 pmHow can anyone answer that question? It is totally open-ended.Jumper cables are not that expensive. It is most important to get proper quality ones with genuine copper conductors, and not fake ones made of aluminium (or even worse, steel).You find out they are not big enough if they start getting hot when in use. If they get too hot, you need to get bigger ones. That's basically it. Practical testing to find an answer.

author: Simon
author_rank: Unknown
timestamp: July 16, 2025, 07:57:29 pm
content: As I have already said, just stop. You are going to end up injuring yourself and others!

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 17, 2025, 06:21:10 am
content: Quote from: BeBuLamar on July 16, 2025, 07:18:04 pmIs that not a typo? 30A and not 300A because 30A is not considered very high is it?Others had mentioned hundreds of amps before for a short time so 30 doesn't seem to add up from that prediction.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 17, 2025, 06:36:21 am
content: Quote from: IanB on July 16, 2025, 07:40:47 pmHow was I supposed to know it can't be made into a simple calculation like most other electrical things? I am not an expert like you. I don't understand why it isn't calculable? since I gave the spec sheets of both batteries?

author: Simon
author_rank: Unknown
timestamp: July 17, 2025, 07:21:02 am
content: Quote from: electroniclearner820327 on July 17, 2025, 06:36:21 amThat is why you should just leave well alone and not keep trying to hurt yourself.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 17, 2025, 10:05:49 am
content: Quote from: Simon on July 17, 2025, 07:21:02 amI am asking questions to be safe and not hurt myself.I see you have had it in for me, I have no idea why since I didn't instigate or have little at all to do with the trouble, since the Voltmeter thread and have typecast me now, based only on skimming a couple of comments on my threads, as some bumbling idiot and deride any post I make now in a similar vein.

author: madires
author_rank: Super Contributor
timestamp: July 17, 2025, 10:42:23 am
content: A starting point for learning about batteries:https://batteryuniversity.com

author: tunk
author_rank: Super Contributor
timestamp: July 17, 2025, 10:48:09 am
content: Rules about safety are one thing, but understanding what's going on is equally important.If you understand what's going on, you're less likely to do stupid tings.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 17, 2025, 12:12:20 pm
content: Quote from: electroniclearner820327 on July 17, 2025, 06:21:10 amIt's a guess as I don't know but I would imagine quite high. I said just to measure it. Any way doing so you will charge the battery at a rate much higher than recommended by the battery manufacturer. You will at least shorten the life of your battery.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 17, 2025, 12:18:28 pm
content: Quote from: electroniclearner820327 on July 17, 2025, 10:05:49 am

author: Simon
author_rank: Unknown
timestamp: July 17, 2025, 01:18:51 pm
content: Quote from: electroniclearner820327 on July 17, 2025, 10:05:49 amThis thread is the same as the voltmeter thread, you ask what seems to be one question but actually wanted an answer to another implied question that lacks information.Let me explain how this could be dangerous. You don't even go putting lead acid batteries in parallel! Narrow boat owners can tell you some stories about people who wanted to add another battery to their boat. But as the old and new battery of the same chemistry were not identical one gets rather hot and fires start. You want to put two dissimilar chemistries together, as I said twice now, for the third time: stop, don't do it.To put two lead acid batteries in parallel they have to be the same, brand new and preferably from the same batch. Naturally putting lead acid batteries in series is even riskier if they are not identical brand new batteries.It's not that I am on your case, I am a moderator, and I keep getting reports about your threads, when I look at why there is such lot of arguing over your question it is because you are clearly out of your depth and asking the wrong questions.

author: golden_labels
author_rank: Super Contributor
timestamp: July 17, 2025, 01:40:45 pm
content: Quote from: electroniclearner820327 on July 17, 2025, 10:05:49 amIt’s rather that people have some observation skills and can connect the dots. Multiple of your threads reveal that you:Engage in projects beyond your level of experience and understanding.You experience weird and unexplained failures with them.You inquiry about potential causes, but there is no sign of any attempt to address those issues.There is a lingering odour of the naïve DIY attitude.Now you ask about something that may easily end in acatastrophic failure. We already know you have multiple car batteries connected in a convoluted way. Those are power levels that may for a moment reach values comparable to a small rock concert stage. You ask about how to hold an exploding firecracker in your hand and get angry, because people tell you to not do this.Yes, it is perfectly fine to ask and learn about doing things safely. The problem is: you refuse to accept that the question itself is wrong. You are asking about current capacity in a mental model that is inadequate for the problem at hand. Of course you yourself can’t see it yet,(1)but this is exactly why it’s worth listening to more experienced people. And they tell you to halt right there.If you want a stupid, uncaring answer: 15–20 mm2of braided copper. This answer is accurate and technically correct, yet wrong. So don’t blame me or anybody else here, if your van turns into charcoal, your lose a hand, or hydrogen or sulfuric acid cloud explodes in your face.(1)One can’t know what they don’t know.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 17, 2025, 03:21:39 pm
content: Quote from: golden_labels on July 17, 2025, 01:40:45 pmThat is a bold faced lie or you simply haven't taken the time to understand the setup and just say 'wrong'. My battery setup as it is, NOT, this parallel jump cable question, is perfectly by the book for installing a dc-dc charger between a starter battery and leisure battery.I am not sure why you all are saying it is so bad to link them by jumper cables? I made a previous thread and no one was writing that. They just wrote to be careful. I have not picked this idea out of the air. There are several threads on campervan forums where people did it to no ill effect and am just going from those datapoints.Why would either battery explode? I have read, yes, it isn't good for either battery to do it and may well shorten their life, but not that there will be explosions. If you say it is wrong, say why and how it would explode giving real world physics of why it would happen. I have even emailed the maker of the leisure battery and they replied yes it is ok but only do it in an emergency as it is bad for the battery. Nothing about DO NOT DO THIS AS IT WILL EXPLODE. So where is the reasoning of explosions?What you link above I can see from the url they plugged them the wrong way round, well that is something that could happen any time you tried jump starting a vehicle so it is not any added risk to what I am doing here. Normal safety procedures apply.Again, it is coming from real world examples of people doing it to no ill effect that they could note.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: July 17, 2025, 03:33:58 pm
content: Faringdon?

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 17, 2025, 04:03:20 pm
content: Hereis a thread on a campervan forum discussing the very same thing and at least one report of it being done without issue. So not total pie in the sky.Lol and look at this quote of another 'success' using a much more ropey method:Quote

author: madires
author_rank: Super Contributor
timestamp: July 17, 2025, 04:25:20 pm
content: Quote from: electroniclearner820327 on July 17, 2025, 03:21:39 pmThis thread started with a question about paralleling batteries via a jumper cable for charging purposes and now there's suddenly a charger between the batteries? Any more twists?

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 17, 2025, 04:40:24 pm
content: Quote from: madires on July 17, 2025, 04:25:20 pmNope. You are not understanding what I wrote.They made the claim mycurrentsetup was incorrect, which is where i mentioned the charger.This thread is about a hypothetical situation where I would want the jumper cables. There are no twists there, just a lack of comprehension of what I wrote.

author: IanB
author_rank: Super Contributor
timestamp: July 17, 2025, 04:41:24 pm
content: Quote from: electroniclearner820327 on July 16, 2025, 09:51:52 amRight at the start, you are inconsistent. Which is it, temporary or continuous?If temporary, you just buy a set of jump cables and connect them temporarily following the recommended procedure. Nobody cares about the current rating, they just buy a set of cables and use them.If continuous, don't do that. It is bad for many reasons.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 17, 2025, 05:01:37 pm
content: Quote from: IanB on July 17, 2025, 04:41:24 pmBy continuous I meant not only to jump start but rather to leave for 15+ minutes in order to trickle charge to equalize both batteries.Temporary in that I would disconnect after this short time frame.

author: IanB
author_rank: Super Contributor
timestamp: July 17, 2025, 05:23:59 pm
content: Quote from: electroniclearner820327 on July 17, 2025, 05:01:37 pmJump cables don't tend to do a trickle charge. There is no current limiting, so what they do is a fast emergency top-up charge. In this case, having thinner cables can perhaps be better, as this will limit the magnitude of the current surge.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 17, 2025, 07:48:17 pm
content: Quote from: electroniclearner820327 on July 16, 2025, 04:06:56 pmI'd say pretty thin wires. Something like 0.1 square mm, and make them long too. The goal is that the resistance of the wire is big enough to limit the equalization current to a safe value. You can calculate the maximum equalization current by first taking the difference in battery voltage between a full and an empty battery, and divide that by the maximum charge current.After the batteries are equalized, you can use wire size based on the the currents that your system can handle. The cabling should always be able to handle more current then the fuses.

author: Simon
author_rank: Unknown
timestamp: July 17, 2025, 08:51:18 pm
content: Quote from: Roehrenonkel on July 17, 2025, 03:33:58 pmNo, same but different, must be related. I mean can't be him, hasn't put power supply design going to china into it yet and it's been long enough.

author: Simon
author_rank: Unknown
timestamp: July 18, 2025, 06:44:59 am
content: Quote from: electroniclearner820327 on July 17, 2025, 04:03:20 pmYes I pretty much did that myself. I was at a town fete running a stall and when we went to pack up a guy on another stall found his car would not start. I had a leisure battery that I was not that fussed about and I knew it was not that charged so I connected it across his battery for a few minutes with jump leads and monitored it constantly. Then he started his vehicle. Like I say, I was not concerned about damaging the battery as it was old and I was amazed it even worked, but it was a one off and I knew what I was doing and would never have done it with the new battery I bought not long after.Again we are talking same chemistries, you are talking about different and one of them is very techy and must be used with a BMS.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 18, 2025, 08:06:22 am
content: Quote from: Simon on July 18, 2025, 06:44:59 amYes, on more consideration seems not worth it. The only reason really for it was the fear of an alternator failure leaving me stranded somewhere. I was given a good suggestion of instead, to cover that eventuality, get a spare alternator to keep as a backup.That would even be cheaper than those leads if I got a refurbished one.I have already changed this one once myself. It is not something I would really enjoy doing at the side of the road but doable.However that infamous voltmeter thread is an effort to be able to keep an eye on the state of things in that department to prevent such an eventuality in the first place.

author: MrAl
author_rank: Super Contributor
timestamp: July 18, 2025, 09:46:39 am
content: Quote from: electroniclearner820327 on July 16, 2025, 09:51:52 amHi,Are you sure you wrote that correctly?You can charge a battery but you do not charge a starter you just energize it with a power source like a battery. By putting a battery and starter in parallel that just runs the starter.If you want to charge a battery with another battery you have to look up the specs on both batteries. They will have a maximum drain current and a maximum charge current. You should not go over that.Also, to charge the first battery from the second battery, the second battery must have a voltage that is higher than the first battery. The voltage difference and the resistance of the cables will determine the max charge current, and it will taper off as the first battery becomes more and more charged.There are various cautions, the first one is to wear eye protection in case something unforeseeable goes wrong. Note 'unforeseeable' means there is no way you can predict what will happen.This is because batteries can present very unusual and varied scenarios which can cause either of:1. Large current2. Small or medium current3. No current#1 is the most dangerous and can happen if the voltage difference is very large. This is when an explosion can occur. This means you should measure the voltages first and if needed add some resistance in line with the cables which can be removed once the voltages get closer to each other.I can't stress enough that no matter what you do eye protection is a must. If something gets into your eye or eyes and causes permanent damage, you can't reverse time and go back and fix it. Even if it's not permanent, it could cost a huge amount to get the required eye surgery. If you don't have eye protection handy, get some. If not, at least block your eyes with your hand or arm when you first connect the setup and for some seconds after that. Always keep in mind that **** happens

author: Gyro
author_rank: Super Contributor
timestamp: July 18, 2025, 12:16:51 pm
content: Quote from: electroniclearner820327 on July 18, 2025, 08:06:22 amI have to confess that I am confused. In your original thread (the one I linked for you), you said that the charge light was going on and off. in the voltmeter thread you said "THERE IS NO MALFUNCTION THAT NEEDS ADDRESSING" and now you are talking about carrying a spare alternator and changing it at the side of the road.This does seem to be rather a fixation on a single, and rather reliable, component. There are a host of components in the engine bay that could leave to totally stranded at the side of the road, eg. Starter, timing belt / chain (potentially terminal), auxiliary belt, hoses, engine management, clutch, gear box, brake master cylinder, water pump etc. etc.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 18, 2025, 03:02:14 pm
content: Quote from: MrAl on July 18, 2025, 09:46:39 amYou were misled by his imprecise language (he's been told about that before).When he says "starter" and "leisure" he means "starter battery" and "leisure battery".I can't believe the remarkable amount of good will he is enjoying will continue if he keeps failing to write clearly.

author: MrAl
author_rank: Super Contributor
timestamp: July 18, 2025, 04:55:57 pm
content: Quote from: SteveThackery on July 18, 2025, 03:02:14 pmHa ha, ok thanks for the info there

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 18, 2025, 05:03:09 pm
content: Quote from: SteveThackery on July 18, 2025, 03:02:14 pmI think when he said starter battery mean the lead acid battery with high cracking amp to start his van but it's not good if it gets discharged very much. The leisure battery may not provide high current but has higher Ah rating and can be discharged to a almost empty to supply him with electrical power when the van engine is not running. He has no electricity other than his alternator and his solar panels.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 18, 2025, 06:52:44 pm
content: Quote from: BeBuLamar on July 18, 2025, 05:03:09 pmSeems you got it perfectly well.The other guys just trying to spin a narrative again to get me in trouble.

author: MrAl
author_rank: Super Contributor
timestamp: July 18, 2025, 08:04:36 pm
content: Quote from: electroniclearner820327 on July 18, 2025, 06:52:44 pmHi,In technical forums you have to be a little more concise when you speak (type) or else you will get off the wall results and all sorts of questions. That will delay the help you can get from the many experts here. There are the mockers though who are looking to mock because they think that makes them look better. I did not read all the posts here so I can't say if I've seen any here or not.You may not realize how lucky you are. Back when I was first getting into the field we never had an internet, we just had libraries, and some of them were a long bike ride away. Now you can type questions into forums and get results right off, or you can search with a search engine. If you feel like it you can experiment with 'ai' too. We never had that. I was even lucky to find the books I wanted at the various libraries. Rutgers University had the best, but to get some books I had to hope to at least find out where they could be found and have my local library get one delivered, and then I only had a limited time to study it.Be happy, you have all this and more

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 19, 2025, 06:26:36 am
content: Quote from: MrAl on July 18, 2025, 08:04:36 pmPersonally I preferred the world pre-internet.I was the last generation - 90s kid - to grow up partly without it.Well it is a double edge sword. You can say information is at your fingertips but there is no bar for the information and we are in the era if misinformation. You mention AI and that can be used to make deep fakes.We can argue whether it is good or bad to have all this information available. It is just as likely to be bad information as good.I am not saying specifically for this forum, just in general.Most of your searches you make online are loaded with adverts and other spam, everything competing for your attention. So it isn't quite the enlightened utopia of free flowing high quality perfectly researched and sourced, information you make out.

author: MrAl
author_rank: Super Contributor
timestamp: July 19, 2025, 01:19:29 pm
content: Quote from: electroniclearner820327 on July 19, 2025, 06:26:36 amYou are reading too much into this I never said it was perfect. If you don't like the internet, then get off it and take a ride to the library and see how much fun that is trying to get detailed information.Internet information can be riddled with errors, you just have to know what to look out for.Also, some of the folks here have 50 years of experience in these areas of science.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 19, 2025, 02:56:38 pm
content: I like the internet but I do love a good library. Where I live now I do not have access to a good library. I really miss it.

author: Grandchuck
author_rank: Super Contributor
timestamp: July 19, 2025, 03:00:34 pm
content: Yeah, browsing the stacks is wonderful.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 19, 2025, 07:56:19 pm
content: Quote from: electroniclearner820327 on July 17, 2025, 03:21:39 pmSometimes when a lead acid battery is being charged really fast, or when it is approaching fully charged and current is being pushed in, the battery can release hydrogen gas. This is explosive, obviously, so if there is a spark - such as from connecting or disconnecting jump leads - there is a risk of explosion.I think it's a pretty slim risk, myself. If you ask people if it really happens, many will tell you about some guy at their workplace who blew his eardrums out, but if you go on to ask: "But did you actually see this with your own eyes?" the answer is often "No, but...".Anyway, it's a non-zero risk that's easily avoided, so why take the risk.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 19, 2025, 08:01:15 pm
content: Quote from: electroniclearner820327 on July 19, 2025, 06:26:36 amI totally disagree. When it comes to technical stuff, the amount of good information greatly exceeds the bad information, in my experience. Techie geeks get really agitated when they see wrong information (it triggers geeks) so they put a lot of effort into putting it right.Obviously there's bad information out there, but it's nothing remotely like the 50% you claim.

author: tooki
author_rank: Super Contributor
timestamp: July 19, 2025, 08:20:21 pm
content: Quote from: electroniclearner820327 on July 18, 2025, 06:52:44 pmNo, truly it isn't that.The issue is that getting to the core of your questions is spectacularly difficult because of your communication style. There’s a lot of chaff to dig through, and imprecise language requiring interpretation and guesswork. People get frustrated by that. In contrast, really good technical communicators are concise, accurate, and precise, while also providing the necessary information readily.Just remember that if someone gives you feedback, it’s because they want to help. If they didn’t want to help you improve, they’d just insult you without feedback.

author: MrAl
author_rank: Super Contributor
timestamp: July 19, 2025, 09:35:09 pm
content: Quote from: BeBuLamar on July 19, 2025, 02:56:38 pmHi,Yeah, I live farther from Rutgers now so it's much harder to get to.I don't miss having to find the books on the many shelves though even with the use of the 'card catalog'

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 20, 2025, 02:11:04 pm
content: Quote from: MrAl on July 19, 2025, 01:19:29 pmI have been to university and got my degree thanks so have a good idea of how real libraries work as well as the internet.I never had an issue 'getting detailed information' from real libraries. I would say on the internet it was worse because most of the useful stuff was behind paywalls.Sure they often didn't have what you wanted in libraries but at least if they did it was free. Going from memory of almost 2 decades ago anyway.I didn't do my degree in electronics or anything to do with it so maybe a very different situation.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 20, 2025, 02:13:33 pm
content: Quote from: SteveThackery on July 19, 2025, 08:01:15 pmI wasn't relegating the discussion to techie stuff. The claim was made only about the internet at large.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 20, 2025, 02:36:23 pm
content: Curiously which LiFePo4 "Leisure" battery do you have? It may have a BMS built in and in which case you wouldn't have problem simply connect it to the alternator for charging.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 20, 2025, 02:44:11 pm
content: Quote from: BeBuLamar on July 20, 2025, 02:36:23 pmAlready posted the link to the tech sheet more than once in this thread! Why am I going to link it direct to the alternator? The whole reason for the linking them is if the alternator was broken. It is already charged by the alternator via the starter/dc-dc charger.

author: MrAl
author_rank: Super Contributor
timestamp: July 21, 2025, 08:27:51 am
content: Quote from: electroniclearner820327 on July 20, 2025, 02:11:04 pmHello again,Oh I hear ya when it comes to the paywalls. When that **** started it was very disappointing to say the least. Suddenly the internet went from a place to find and share free information to a way to pay for all sorts of stuff including stuff you shouldn't have to pay for. And yes, the best stuff comes at a premium cost.I also share your thoughts on accuracy on the web. There are some things that are very difficult to work with because they have errors that mess up the whole thing. Even very advanced and knowledgeable authors have articles on the web you can't use entirely because there are errors halfway through that can only be rectified by redoing the entire set of calculations. You would think they would be smart enough to proofread their own publication.On the other hand, I have also found errors in published hard cover books in the fields of math and science. Circuit analysis, mathematics, you name it, fall victim. I guess nothing we can do about this except try to spot the errors and fix them.When I look over the years though, I find the internet is easier to work with because I don't have to go anywhere to get the information I do manage to find. There is a chance this could change now though because now I live about one block from what looks like a decent library. Before this I lived about one block from a library too, but it was closed for "renovations" for at least 5 years or more so was not useable anymore. The next one was several miles away. When it was open though I was able to get a lot of information but it took time to get it sometimes days or a week or two.I should also note that the works that I have published have not been perfect either as typos sometimes come about. I try to be as careful as possible though and correct errors as soon as I find out about them. Lucky for me there have not been many so far.Also, I guess I should point out that it's nice to see people like you interested in this area like electronics and related. It's been with me for almost my whole life, and I like to pass knowledge to others who want to learn. I help college kids all the time get their degrees and with homework in this field through forums like this one and email and phone and in person. Some have made it as far as their PhD and some into job placement.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 21, 2025, 04:57:12 pm
content: Quote from: MrAl on July 21, 2025, 08:27:51 amHi.QuoteI see we were talking different kettles of fish then as I can't say I have ever read a maths or science book voluntarily after I finished high school! Well science yes, I tell a lie, I have read plenty but not with calculations like you mention. More things like behaviorism or other psychology related or maybe a classic like The Origin of Species. Maths though? Nooooo.

author: Sideways
author_rank: Contributor
timestamp: July 23, 2025, 12:00:36 am
content: To the O.P.Maybe think about it like this:If you were ever to try and pull enough current through these jump leads to actually start the vehicle, then your jump leads should be as thick as the wires are to the starter motor. And there are no fuses in those.So called "cold cranking amps" pulled through those wires can be 400 or 500Amps for 30 seconds or more. The starter motor wires are thick enough that they may get hot, but the battery runs out of energy before the wires melt.If you connect a flat battery to a fully charged one, you should expect seriously big currents for a short time.No one can give you an exact answer because it depends on the details of the batteries you connect together, what condition they are in and their state of charge.Just understand that if you effectively short circuit a battery through your jump leads, you could be looking at hundreds of amps.You may not be able to do the maths for it, but big batteries have the potential to hurt you all the same.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 23, 2025, 10:13:19 am
content: I tried to search thru the thread to find out what kind of LiFePo4 battery the OP has. I only know it's 100AH 12V but don't know anything beyond that. I tried to find out if it has a built in BMS.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 23, 2025, 03:23:50 pm
content: Quote from: BeBuLamar on July 17, 2025, 12:12:20 pmQuote from: electroniclearner820327 on July 16, 2025, 04:06:56 pmSpeaking of BMSes, I am thinking of getting another battery of the same to increase my total due to increased power consumption but the manufacturer is telling me that if the existing one has had too many cycles already then they will not be able to 'communicate' properly via bluetooth. This seems all very convoluted. Why all the bluetooth nonsense? I hate that stuff and don't own a smartphone. Unnecessary rubbish.I would never have guessed I would be blocked from upgrading due to some bluetooth tomfoolery.

author: IanB
author_rank: Super Contributor
timestamp: July 23, 2025, 03:30:52 pm
content: Quote from: electroniclearner820327 on July 23, 2025, 03:23:50 pmIt's not to do with Bluetooth. If putting two batteries in parallel to increase capacity, both batteries need to be new and matched for type and capacity. Putting and old battery and a new battery in parallel may not work properly. It is not Bluetooth that is stopping you, it is physics.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 23, 2025, 04:39:16 pm
content: Quote from: IanB on July 23, 2025, 03:30:52 pmWhat are the physics?Does less than 1 year old for the current one count as old? Got it around december last year and been using all the time since.This is very inconvenient if I am not still able to use the current one. Having to sell it probably for a fraction of what I bought it for? and get 2 new would be a blow. Well if I had to get rid of current one I would just get a single higher Ah one.Surely there are some tricks to let me continue to use this and add another?Reading up some more the general view online is that it is fine to mix different aged batteries and it is mostly a sales pitch when it is advised against.One example

author: Grandchuck
author_rank: Super Contributor
timestamp: July 23, 2025, 05:34:01 pm
content: The physics are straightforward. Assume an internal resistance of 5 millohms and only a 0.1 volt difference in battery voltages.I = 0.1/.005 = 20 AmpsThat is a significant current. Consider both batteries with the same internal resistance and it is less current ... but still 10 A.

author: BeBuLamar
author_rank: Super Contributor
timestamp: July 23, 2025, 07:35:19 pm
content: Yeah your leisure battery doesn't have a BMS built in. It does allow to charge at 100A rate which I think may be fine if you just connect the starter battery and the leisure battery together. Use cable that can handle 100A. If the battery is discharged a lot the current may be more than 100A but not by much I don't think so. Any way don't the OP has a mean to measure the current?

author: PlainName
author_rank: Super Contributor
timestamp: July 23, 2025, 09:50:23 pm
content: Quote from: electroniclearner820327 on July 23, 2025, 04:39:16 pmYou seem to have found sources of advice in other forums. The bits in those forums that warn you about bad consequences, like has been warned here, you've ignored despite quoting those forums as a source saying what you want to do works fine.So... why are you asking here? Isn't it enough that the several other forums have given you the answer you want? Surely you don'tneedthe entire internet to agree with you <insert obligatory XKCD>, so you already have your answer in those other places. This forum doesn't seem to be the right one for you.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 23, 2025, 11:12:38 pm
content: I was about to ask if anyone had spotted the troll, yet. @PlainName beat me to it.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 23, 2025, 11:17:53 pm
content: Quote from: SteveThackery on July 23, 2025, 11:12:38 pmUm, I don't think so (assuming you mean the OP here).Unless you define "troll" as "someone whose posting style I don't care for", which is a misuse of the term in my book.Yeah, the OP has some problems with their posting style. But writing them off as someone who is just trying to rile people up here, or whatever, just doesn't fit.Now to continue with our regularly scheduled programming, which concerns ... something about jumper cables, wire gauges, etc. ...

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 24, 2025, 03:20:25 am
content: Quote from: BeBuLamar on July 23, 2025, 07:35:19 pmHow did you figure that? It shows the information right there on the page on the right hand side with a big heading BMS INFORMATION.https://cdn.shopify.com/s/files/1/1347/0997/files/NEW_105Ah_Spec.pdf?v=1712046085QuoteI already wrote, after the many recommendations and reasons against it, I don't want to link the start and the leisure battery together any more. I am now asking the question of buying another leisure battery the same make/model as the existing one in the link above. The only question now is, since it is almost a year old, if I can mix the aged one and new one.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 24, 2025, 03:25:18 am
content: Quote from: PlainName on July 23, 2025, 09:50:23 pmThanks for your passive aggressive reply. Much appreciated.It is because this is a forum specializing in electronics and getting a diverse range of feedback I can then weigh up all the replies and make an informed decision.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 24, 2025, 03:31:04 am
content: Quote from: Analog Kid on July 23, 2025, 11:17:53 pmThanks for the vote of support.Exactly as you say, I am fed up of people using troll to mean anything that is not exactly to their liking.I have read the forums and seen not only myself being accused of it but others too when any kind of disagreement takes place. Instead of asking for clarification about something they instead the label 'troll' is just thrown out.Imagine in the scientific community whenever there was not complete consensus they just call each other trolls.It is an attempt to shut down the other person and stop any kind of understanding or dialogue.Troll has now become shorthand for "I can't be bothered trying to understand you so will just call you a name so I don't have to".It is no surprise that you, good sir, Analog Kid, being one of the patient ones who has actually taken the time to actually read what I am asking, are able to see those accusations are fallacious and scurrilous. Not saying you are the only one, MrAI too is another one that springs to mind.What use is the beginner forum if new users, who are not used to the posting style yet, are just 'shut down' as trolls?

author: tunk
author_rank: Super Contributor
timestamp: July 24, 2025, 11:05:25 am
content: Quote from: electroniclearner820327 on July 24, 2025, 03:20:25 amFrom the datasheet:Maximum Discharge 1C (105A)Maximum Charge 100AMaximum Discharge 100ACharging Current : up to 250AConflicting specs -> not very trustworthy?And if you connect fully charged and fully dischargedbatteries in parallel, then the protection may kick in.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 24, 2025, 11:08:16 am
content: Quote from: Analog Kid on July 23, 2025, 11:17:53 pmNothing to do with posting style. Nothingat allto do with "disagreement". My suspicion is that the OP is revelling in the attention he's getting in this and other forums, and as such is milking the thread for more attention instead of taking what he has learned and using it to resolve whatever issue he has out there in the world.I might be wrong, of course, but I'm making an observation and expressing it.

author: Grandchuck
author_rank: Super Contributor
timestamp: July 24, 2025, 12:35:56 pm
content: Psychology experiment?

author: Zero999
author_rank: Super Contributor
timestamp: July 24, 2025, 12:46:10 pm
content: Quote from: electroniclearner820327 on July 16, 2025, 10:08:37 amThat's what you asked in the subject field.Determining the correct conductor size depends on numerous factors:Current.Conductor material.Frequency: high frequency current is confined to the surface by the skin effect.Ambient temperature.Insulation temperature rating.Surrounding material.Ventilation.Then there's the issue of whether someone can be burned. The insulator might be rated to 200oC, but if it gets that hot, then it can burn someone if it's accessable.Yes not all of the above are relevant to your application. It's just for information.

author: electroniclearner820327
author_rank: Regular Contributor
timestamp: July 24, 2025, 04:04:25 pm
content: Quote from: tunk on July 24, 2025, 11:05:25 amPeople are still answering the question which I have said above I abandoned long ago.QuoteNow people will probably complain I didn't make a new thread but I got criticized when I did make new threads that they aren't all in one thread, so I can't win really.

author: PlainName
author_rank: Super Contributor
timestamp: July 24, 2025, 04:33:24 pm
content: QuoteThat's the nature of forums. You can't expect someone to pop in and read all 78 messages with full concentration before finally posting the answer to the question asked at the start. Well, I guess you could expect that if you were paying them to waste their time on you.How about, when you spring new stuff in random places, you also just edit the first post to say you've changed your mind and want to do things a different way? Then someone joining in afresh will be hip to your current whim without spending an hour to get here only to get berated for answering the wrong thing.

author: Gyro
author_rank: Super Contributor
timestamp: July 24, 2025, 05:03:53 pm
content: Quote from: PlainName on July 24, 2025, 04:33:24 pmThat should be 'edit' as in 'append a dated edit to the end of the post', so that new people don't wonder what the hell people who replied earlier have been talking about.

author: Zero999
author_rank: Super Contributor
timestamp: July 24, 2025, 06:23:06 pm
content: Quote from: Gyro on July 24, 2025, 05:03:53 pmIf it's a completely different question and not just for clarification or to add more information, I prefer the edit to be at the start of the post, to save having to read though the whole thing.