12V DC routing - Page 1
Forum section: electronics / beginners

author: paulca
author_rank: Super Contributor
timestamp: January 18, 2022, 04:05:17 pm
content: Hi,I know I asked this last year, but I didn't get a viable solution then and have decided with an alternative.In short I have 12VDC solar power available in the garage. I would like to use that 12VDC in the office, 10 meters away in the upper floor. Originally I thought as the system is rated for 10amps, I would need to route 10Amps, or 120W and needed to use a boost converter to save on expensive thick cable by transmitting the DC at 50V or higher.Now I have a plan B, which should be cheaper and easier. Ballast. A can put a lead acid in the office, run the 12V up over 1.5mm cable and put a CC/CV buck converter on the end, connected to the lead acid. The CC/CV PSU will simply limit the charge current on the 10 meter wire run to 2 Amps. So it will effiectively charge the office battery 24/7 at no more than 2Amps. Even if I pull 20 Amps from it to run a DC/DC power supply at 20Amps.Anyone see any problems with this approach? It's basically running a remote CC/CV charger as a load on the existing solar system. If it goes low battery, it will shut the load off.

author: tszaboo
author_rank: Super Contributor
timestamp: January 18, 2022, 04:13:01 pm
content: 10m 2.5mm cable is 21 EUR in the local home improvement store

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 18, 2022, 04:19:07 pm
content: The problem I see is hours of sunlight. Assuming your charging source is PV then for example on a short winter day you will only be able to transfer 10AH to the battery.

author: paulca
author_rank: Super Contributor
timestamp: January 18, 2022, 04:31:48 pm
content: Quote from: tszaboo on January 18, 2022, 04:13:01 pmYes, but if I start pulling more than a few amps the voltage drop will start to bring me well under 12V and may cause other issues.I think 2.5mm at 10A still results in something like a 1.4V drop.Mostly the 12V will be used to run other battery chargers, headphone amps and electronics bench supplies. Basically a lot of low wattage stuff. However the DC/DC bench supplies I have can buck 20Amps and boost 5Amps (input limited). So there is a use case for temporary, periodic, short term high current draws that would not be possible with 12VDC over any civilised thickness of cable without a >1V drop.Quote from: fourtytwo42 on January 18, 2022, 04:19:07 pmIt's backed by a 100Ah battery. So as long as I keep an eye on the main solar battery levels over winter and don't drain it. It should be fine.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: January 18, 2022, 04:35:53 pm
content: Your 12v battery will not like being kept at 12v. It will need something like 14.4v absorbtion charge and then storage at a float voltage of something like 13.8v.This seems like a very complicated and expensive solution to a problem that's not really much of a problem.You can work out volt-drops for yourself based on a 10m circuit and how much load you forsee drawing, but even 16sqmm wire is only £1.67/m and that will be good for <5% volt drop at 20Ahttps://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.htmlYou can buy by the metre from here (or tonnes of other places)https://www.tlc-direct.co.uk/Main_Index/Cable_Index/Singles_1/index.html

author: paulca
author_rank: Super Contributor
timestamp: January 18, 2022, 06:05:08 pm
content: Quote from: DenzilPenberthy on January 18, 2022, 04:35:53 pmThat's why I'll use a basic CC/CV charger on it. That will at least give it 14.40V boost.Quote from: DenzilPenberthy on January 18, 2022, 04:35:53 pmIt's not exactly expensive, I already have the battery and beyond the cable it's a £10 CC/CV buck/boost module off AmazonQuote from: DenzilPenberthy on January 18, 2022, 04:35:53 pm2 reasons.1. I need 2 cores, ideally brown/blue or black/red which looks like £40 for 25 meters. Twice. That's £80 + clips. The 1.5mm 3 core, outdoor UV resistant, round black stuff on Amazon is £35 delivered for 25m. (I have not measured the distance exactly).2. It has to go through 2 walls and be clipped to an exterior wall for routing. I do not at all fancy trying to clip up 16mm cables to an upstairs room.Anyway. I figure the CC/CV charger and the lead acid are a red herring. It's still just a basic 12VDC circuit. I can decide to put a buck/boost, charger or a funky lamp on the end of it.It just comes down to the pricing and hassle of the cable. I make that choice, install the cable, I live with it or use a battery to give local high current storage if/when needed.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 18, 2022, 06:45:27 pm
content: What are you running in the "office" that requires 12V @ 10A?A cheap and easy solution is to have 12V -> 240V 200W inverter (The kind designed to go in a car, caravan, or boat) and then a standard 12VDC switching supply in the office running off the 240V. Add some sort of remote ON/OFF to save on idle current when not in use.Sure, there will be losses, but there will also with charging and discharging a 12V battery.

author: BeBuLamar
author_rank: Super Contributor
timestamp: January 18, 2022, 06:49:23 pm
content: How efficient is the type of converter you want to use? I much rather take the loss in the cable.

author: paulca
author_rank: Super Contributor
timestamp: January 18, 2022, 07:21:55 pm
content: Quote from: BeBuLamar on January 18, 2022, 06:49:23 pmIt's not the loss itself I'm worried about. I mean if on 1.5mm at 10 amps it's dropping 2V and wasting 20W as heat to the outside world, it's fine... not ideal, but fine.What isn't fine however is a battery that drops to 12V under 10Amps load, then lossing 2V on the circuit and I end up with 10V to work with.That again is fine. But, I will need to boost it for almost everything useful anyway.The higher voltage alternative, or even the full AC inverter route aims to take care of the cable loss before transmission. Although the point about converter loss +/- cable loss is taken.I suppose it comes down to equations and data.Decide the current, say 10Amps max.Decide the line working voltage range, 10-16VFor a given cable/cost/hassle what is the lossFor the same setup what is the loss in the converter, or converters.Now it sounds like a chore, LOLI imagine how this will work in reality. It will spend 90% of it's time switched off at source and 9% of it's time running 1 or 2, 20W USB charge circuits and 1% of it's time running a LiPo charger at 80W or 20W of lights and a 20W laptop charger on a evening during a power cut. So I should just cap it at 2 amps for the 99% and use mains or local battery for the remainder.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 18, 2022, 07:41:38 pm
content: I've got another idea for you.All you need is a single boost converter located in the garage. Since you'll know the resistance of the 12V feedline to the office, you can design the boost converter to increase it's voltage based on the amount of current being demanded. That way, the voltage in the office would stay more or less constant.EDIT: Link to TI application note. Could be adapted for a boost converter instead of buckhttps://www.ti.com/lit/an/slva657/slva657.pdf

author: Benta
author_rank: Super Contributor
timestamp: January 18, 2022, 08:21:45 pm
content: Why not just use 6 mm2cable?It's cheap and mandated for 16 A installations today.Or if you need it flexible, buy automotive battery cable. 6, 10, 16... mm2at a couple of Euros per meter.

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 18, 2022, 08:36:16 pm
content: Another flexible solution is to buy 2 cheap 3 wire extension cords and tie the conductors together so each cable acts like one big wire.

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 18, 2022, 09:06:03 pm
content: 10m is no big deal, cable runs of this length are common in boats, busses, caravans, etc.Size it appropriately for the expected load and fuse it appropriately for the cable ratingI haven't seen your previous thread but this may be of use to you:https://www.bluesea.com/resources/1437

author: Zero999
author_rank: Super Contributor
timestamp: January 18, 2022, 09:39:35 pm
content: Does the solar panel have a built-in voltage regulator?The last time I used a 12V solar panel, I found it had a much higher output voltage when open circuit, something like 18V. If you don't intend to use the full power output, you might find the voltage is high enough. Put the solar panel at one end of a thick cable and an efficient buck converter, with a low dropout voltage, near the load.

author: Siwastaja
author_rank: Super Contributor
timestamp: January 19, 2022, 03:42:22 pm
content: While 12V isn't optimal for transferring 120W, 10 meters is still just 10 meters! I bet just throwing more copper at the problem is the cheapest and most reliable solution.In other words, 6mm^2 cable. If you happen to find something else with more conductors for cheaper, you can also parallel conductors.Now for a 50-meter link, things could be quite different.

author: paulca
author_rank: Super Contributor
timestamp: January 20, 2022, 02:16:36 pm
content: Quote from: Zero999 on January 18, 2022, 09:39:35 pmYes. The panel is buck converted down to the what the battery charge phase demands or to current limit it when the battery is fully charged.At dawn nothing happens until the panel hits the battery voltage, then it goes to 100% duty cycle on the buck converter effectively directly connecting the panel to the battery.When the sun comes out and the panel is able to push current at much higher voltages, the MPPT chasing algorithm kicks in to track the max power output and bucking that voltage down to the battery required charge voltage of 14.40 or 13.60.If the battery gets to be 14.40V and is pulling less amps the buck converter will end up very short duty cycle which will cause the panel to rise towards open circuit voltage.The "load" side is directly connected to the battery with a 10A fuse and an automatic cut out which I have set to 11V.Quote from: Siwastaja on January 19, 2022, 03:42:22 pmYou are probably right. For most of the usage it won't be high amps and the USB chargers will usually accept auto-motive 9-16V.The odd requirement to have 12V or greater I can use a PSU to boost it and take the losses.

author: paulca
author_rank: Super Contributor
timestamp: January 20, 2022, 04:55:44 pm
content: To save myself hassle and making a mess of it. I phoned my rather casual spark to install 6mm2 and hopefully doesn't cost and arm and a leg. I don't think it will knowing him.It will be twin and earth of course. I was thinking to parallel and get any advantage I would need 4 cores, but then I thought about it and adding the earth in parallel to the + might mean less voltage drops on the high side and overall circuit resistance will be lower.

author: Zero999
author_rank: Super Contributor
timestamp: January 20, 2022, 05:09:41 pm
content: Quote from: paulca on January 20, 2022, 04:55:44 pmWhy parallel with earth with the positive side? Is the negative side earthed? If so, parallel the negative with the earth. Otherwise, if it's not earthed, it doesn't matter whether you parallel the positive, or negative with the earth conductor.

author: paulca
author_rank: Super Contributor
timestamp: January 21, 2022, 04:19:13 pm
content: Quote from: Zero999 on January 20, 2022, 05:09:41 pmNo end is earthed. The earth conductor is redundant.Although... is it?What happens if it get's hit by lightening? Should I earth the cable itself?Actually. I think earthing it would not matter. If it were to have the unlikely miss fortune of lightening strike, which is more likely if it IS earthed.... anything on either end of that cable or anything near it will be vaporised earth or no earth.EDIT: The panel/battery system is 100% floating. Except whatever conductivity to ground the system has from any leakage via air or the bench it's sitting on.I think I did measure it realitive to earth once and it was under a volt battery - to plug ring earth.

author: Zero999
author_rank: Super Contributor
timestamp: January 21, 2022, 04:56:28 pm
content: Quote from: paulca on January 21, 2022, 04:19:13 pmIf it gets struck by lightning then you've got bigger problems to worry about and probably not much more likely if the cable is earthed, since the voltage is so high.

author: paulca
author_rank: Super Contributor
timestamp: January 21, 2022, 05:57:11 pm
content: Quote from: Zero999 on January 21, 2022, 04:56:28 pmWas thinking in terms of streamers. Would they not be far more likely to be emitted from the ends of a copper cable that connects to earth than one that doesn't? The later has an air gap, but maybe as you mention as the potential is so great borrowing just that section of copper while going down the outside of the building would still be preferential airgap or none. Low resistence = high current = vapourised copper.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 21, 2022, 06:46:42 pm
content: Quote from: paulca on January 21, 2022, 04:19:13 pmAsk yourself this: Would you rather have the majority of the energy from a lightning strike dissipated outside your office or inside?If you earth the negative lead to a ground stake (earth) just outside the building and also connect the +12V line to the stake via a spark-gap it'll be a lot safer. It's up to you if you want to take the risk. Personally where I live I wouldn't worry about it since lightning is very rare here. But your location may be quite different.

author: Zero999
author_rank: Super Contributor
timestamp: January 21, 2022, 07:22:24 pm
content: Quote from: Kim Christensen on January 21, 2022, 06:46:42 pmIt's true, connecting it to earth, will help to reduce the voltage a bit, but not much, as the lightning strike is very fast, so the impedance will still result in a large voltage. A screened cable will provide more protection and covering it with an earthed copper strip will be better still.

author: paulca
author_rank: Super Contributor
timestamp: January 23, 2022, 11:19:31 am
content: Anyway. Lightening strikes are rare and as pointed out, if the house gets hit by lightening my 6mm cable disintegrating and the solar system burning, along when what ever is connected at either end, I will have even worse issues at that stage. Especially as my house has no lightening protection to speak off. I don't know how well iron rich red bricks conduct that high voltage. I suppose that also makes it less attractive than the huge aluminium shopping centre building 200 yards away.... and I'm the only house in the street with no TV aerial which should work in my favour. That said I am one of the highest houses in the neighbourhood.Anyway....A small floating circuit with only one short run outside the window to the solar panel is a bit different than a 10 meter 6mm antenna floating.So maybe, I should at least ground the solar panel system to a plug socket earth. Not to protect it from lightening, but to stop it floating to some silly ass voltage in electrical storms etc. I mean just because the once or twice I have measured it, it was within a volt of GND, doesn't mean it's always like that. It could get way off if there is electrical storm activity. No?

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2022, 11:39:24 am
content: Quote from: paulca on January 23, 2022, 11:19:31 amThat's a good idea. It's better to earth the negative, to reduce corrosion problems. The only down side to it being earthed is increased risk of short circuits, if the positive were to touch a grounded object. Obviously a fuse is a must, both to protect the cable and the battery from fire.

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 23, 2022, 06:17:41 pm
content: QuoteIt's possible to have voltage induced by an indirect strike. Another possibility is an electrical leakage/fault in the area or wet/faulty Christmas lights strung up on the garage if you do that sort of thing.ie: I mention the Christmas lights because I strung some LED ones along my aluminum railing one year. It rains a lot here, and while I never got a shock off the railing, I did notice odd spot corrosion on the railing afterwards. The lights also failed because the legs of some LEDS had corroded away. They just bend the legs over a plastic "bulb base" and jam them in the socket. Not waterproof at all, but were rated for "outdoor use". Whatever faith I had remaining for CSA (UL in the USA. CE in Europe) evaporated that day.

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2022, 08:54:05 pm
content: Quote from: Kim Christensen on January 23, 2022, 06:17:41 pmYes connecting to earth will help to protect against induced transients. A transient voltage suppressor diode is also a good idea. I've had a problem with an LM317 based float charger, a couple of solar panels and lead acid batteries: a 24V system. The regulator kept failing randomly, which was fixed by adding a zener diode between the input and output of the LM317.

author: paulca
author_rank: Super Contributor
timestamp: January 26, 2022, 10:42:25 am
content: Quote from: Zero999 on January 23, 2022, 11:39:24 amI'm all fused upBattery is fused at 10 Amps with 16AWG wire to the solar system which has a 10Amp load fuse. 16AWG to the caravan/boat distribution panel. 5 Amp inline fuses on all those switched outlets. This use case will require a 20Amp fuse on the 6mm (technically 6mm should be good for over 30Amps, which should never be blown as the 10Amp to/in or from the controller will go first.The spark is going to leave the tail in a surface box for me. What I need to decide is how I terminate it. For some reason I have a vision of a set of 4, 2xpairs of Black Red 4mm banana ports on the surface mount box. It's that or DC barrel sockets or something. Maybe I should hardwire it to another 12V RV distribution panel at the other end. Thoughts?

author: paulca
author_rank: Super Contributor
timestamp: February 15, 2022, 04:17:01 pm
content: Tamed spark is just away and I have a lovely tail of 6mm solid core, tuff-someit outdoor cable clipped up neatly between the garage solar panel and the upstairs office.I have it jury rigged with Wago's on a 5Amp fuse and am reading pretty good voltage the far end. Still to load test it but I might junction it better first.

author: paulca
author_rank: Super Contributor
timestamp: February 16, 2022, 04:27:51 pm
content: Initial tests it works fine. On light loads under an amp it barely drops any voltage.Running it at 3 Amps currently, through a boost/buck PSU to run a LiPo charger. 0.5V drop on the whole 12V 6mm setup. The efficiencies of the PSU+Lipo charger is another story.The battery is getting 12V @ ~2.6A. The charger is consuming 12V @ 3.0A and the PSU is drawing slightly more at 11.00V from the panel. It's like 50W for a 40W charge. Gotta love boost/buck and resistive balancing.

author: calzap
author_rank: Frequent Contributor
timestamp: February 16, 2022, 04:58:09 pm
content: Don’t think I would want a lead-acid battery in my office unless it was quite small with a secondary container and a gel or glass-mat type. I’ve experienced a lead-acid hydrogen explosion. Fortunately, it was in an out-building, and there was a wall between me and the battery. It was in a secondary container which was damaged but contained most of the mess. Still, there were acid-coated chunks of plastic scattered around the room. Wouldn’t want it to occur in an office.Mike in California

author: wizard69
author_rank: Super Contributor
timestamp: February 16, 2022, 05:42:45 pm
content: there is not a lot of info here to provide a good answer but so far I'd have to say "none of the above". Now realize I don't know what your goals are but your best return would be to put a micro inverter on the solar panel and use it to reduce the electrical bill continuously. This way you are not wasting a lot of energy to charge a battery and your limited solar panel will always be doing something useful in cutting your electrical bill. You will have to make this legal for the local authority though.Now if this is a backup supply, if that is the goal, then you will need an externally housed battery, charge controller and an inverter and associated electronics/electrics to make the system legal in your area.

author: paulca
author_rank: Super Contributor
timestamp: February 16, 2022, 06:02:21 pm
content: Quote from: wizard69 on February 16, 2022, 05:42:45 pmIt's currently a 50W panel. By the time you put that throw and inverter and try to put it on the grid, it wouldn't get noticed. I mean in the last 2.5 years it has produced 60kwh. A whole whopping £11 UK. When the system cost about £100 all in. It will be a while paying for itself LOLNo, no. If I wanted a AC 240V setup, I'd just pay a certified installer to put 3kW on the roof with approved producer meter etal.This is just an off grid, personal, hobby project. It can and has in the past provided me with a way to run lights, a laptop and my mobile phone for internet while in a power cut.My options were to mothball it or upgrade it. For the later I first needed easier access to the power than trapsing to the garage to run stuff or charge batterys to run stuff. Now I have it on tap in the room 90% of my tech is in.Plan is to keep it off grid, keep it 12V, but put another 200W of panel on the garage roof and find even more bizarre things to do with it.