Lead/Acid Battery Charger : current sense or timer ? - Page 1
Forum section: electronics / repair

author: CeD
author_rank: Contributor
timestamp: May 01, 2017, 02:41:17 pm
content: Hello everyone,I'm repairing a swimming pool equipment which has 2x 12V 18Ah lead/acid batteries, one of which is clearly dead (5,5V, >10 years).The current charger is a Mascot 2240, rated for batteries 12Ah and below,http://www.mascot.no/catalog/battery-chargers/lead-acid/desktop/2240/c-24/c-1310/p-140I'm thinking about replacing it with a more powerful charger, to get a full charge on the batteries, especially modelhttp://www.mascot.no/catalog/battery-chargers/lead-acid/desktop/9940/c-24/c-1310/p-222Both of them are avail. at Farnell here.The problem is that the second charger is "timer" based (the constant current cycle of charge is 2 hours) whereas the first one is current sensing (the constant current part can be shorter, I guess). (Farnell does not have the 2541 model)What difference does it make (sensing or timer) and is one better suited than the other for certain applications ?Or am I overthinking this ?it's just for a swimming pool cover (24V DC motor) that is activated only a few times a week...Thanks !

author: Robaroni
author_rank: Frequent Contributor
timestamp: May 01, 2017, 03:07:17 pm
content: I'd go with current. Batteries are stage charged at a percentage of capacity, usually C/10. You can get a good idea about charging from Trojan's website, they show algorithms.The timer charger probably limits max current dependent on supply but you can run into trouble if say you charge a 1 amp battery and the charger current limits at higher than that.Rob

author: Armadillo
author_rank: Super Contributor
timestamp: May 01, 2017, 03:13:07 pm
content: Firstly, you can discard the battery that is already dead, and don't waste time reviving it.For the other one, if after fully charge and 1 hour of rest, the voltage drop below 12v, then you can consider to replace it as well since its already 10 years ready to write off.On the other hand, because lead acid battery is essentially a constant voltage charge battery, you do not need to invest in another charger. The Mascot 2240 can do the job but just that it will not be that quick to charge the 18AH battery, but it will do the job. Just leave it on the charger until the battery voltage reach 13.6 volt where you can consider it as fully charged. Actually even a cheap constant voltage charger can do a good job of charging the lead acid battery.So, my advice is, instead of spending the money on charger, spend the money on buying 2 new batteries instead.

author: Robaroni
author_rank: Frequent Contributor
timestamp: May 01, 2017, 03:28:45 pm
content: The best Lead/acid charging is three stage. If you want the new batteries to last as long as possible use an algorithm charger.Here's a 3 stage charging profile:

author: CeD
author_rank: Contributor
timestamp: May 01, 2017, 03:56:59 pm
content: Hi, first of all thanks to both of you,Yes I'm gonna replace the two batteries, this is in a house I bought and the previous owner was not really into DIYAnd after ordering two similar batteries at Farnell, I realized the charger itself was also a bit on the short side.I suppose it would charge them anyway, as you say, but as it's probably 10 years old as well, connected 24/7 on the batteries, so I was thinking of replacing it as well. (WIth a better model if possible.)However, it's not possible for me to get the exact same type of charger with the same charging scheme ( = this is the 2541 ) , they don't have that at Farnell, so I have to go with the 9940 if I decide to switch. It's the same as the 2541 but with a different charging scheme.Which leads me to my problem ; are there application "more suited" for the "timer" type of charge, and other for the "current" type of charger ?They are all "3 stade chargers" (constant current, then constant voltage, then standby) ; but they just differ in the duration of the second phase (if I'm reading the specs right).I'm a bit worried about the change in the way it charges the batteries, altough I think I may be "overthinking" this a bit ...

author: Robaroni
author_rank: Frequent Contributor
timestamp: May 01, 2017, 04:06:26 pm
content: I would say, if they are both 3 stage, not to worry too much about it. If you really want to get to the bottom of it then look at the battery manufacturer's charging specs and then see which charger fits the stages better but, again, in most cases you'll probably be be fine with either.Rob

author: CeD
author_rank: Contributor
timestamp: May 01, 2017, 04:27:41 pm
content: Yes that's also what I'm thinking, but since I don't know much about lead batteries ; I just want to be sure I'm not making a huge mistake.I like to read spec PDFs and I may have read these ones a bit too seriouslyI'll let you know how it goes when I receive the batteries next week and I'll do some tests.

author: Armadillo
author_rank: Super Contributor
timestamp: May 01, 2017, 04:34:27 pm
content: Quote from: CeD on May 01, 2017, 03:56:59 pmImagine fill the empty bucket with water. You can quickly fill the bucket by dumping a lot of water say 10 litre/sec for 10 secs then trickle fill it for a certain time. Note that by filling fast, you are exerting higher pressure onto the wall of the bucket. That is essentially those so call intelligent charger algorithm. This process works but imagine you have a bucket initially already filled to 3/4 full [not initially empty], so this adds complication to the so call modern day charger technology. Regardless of by current or by timer, it requires to you have a notion of how much the bucket had been filled to appreciate that kind of technology to be exact precise.. Of-course, some will say smart charger are smart enough to know it, but I am not going to enter into those meaningless debate, you will be happy that the battery last past 2~3 years. For the health of your battery, use a constant voltage charger or your current rather old charger The mascot, until it died. In the mascost specs, you charge until you see the green light. It wouldn't be much of different, I can tell you.In case you must change the charger, consider the modern, cheap and even faster charger, very cheaply available in ebay for hobby electronics nowadays as mosfet prices have drop drastically.But I will still charge mine with constant voltage charger. I don't see why I should be faster by few more hours. I am not in production.

author: CeD
author_rank: Contributor
timestamp: May 01, 2017, 04:47:09 pm
content: Yes this is what I'm gonna do indeed.Plan (A) is to replace the batteries ; keeping the current charger even if "by the book" it's under powered, and see how it goes. After all, it's been like this since 10 years.If really the time it takes to charge them is enormous, or if it never charges them fully at all (never goes green - which I suspect) I'll think about replacing the charger as well. In which case I have to go with the more powerful, but slightly different, model.

author: Armadillo
author_rank: Super Contributor
timestamp: May 01, 2017, 04:51:57 pm
content: This will be interesting to know, please keep us updated. thanks

author: drussell
author_rank: Super Contributor
timestamp: May 01, 2017, 04:52:14 pm
content: Why do you think your charger is undersized for this application?You state that the pool cover motor is only used a couple times per week. As long as your batteries get fully charged back up eventually after this intermittent use, it doesn't matter how slow the charge rate is. A small trickle charger would likely easily suffice in this application, by the sounds of it.

author: CeD
author_rank: Contributor
timestamp: May 01, 2017, 05:18:57 pm
content: Hi Drussel,Well I'm maybe giving too much credit to the "recommended" spec; see end of page herehttp://mascot.blob.core.windows.net/media/1001/2240-tech-spec.pdfIt says above 12Ah is "not recommended" altough I'm not sure what would happen with 18Ah. If it's just slower charging (and the battery will eventually get her 18Ah anyway) then indeed it doesn't need replacing at all. (If it works)The setup is such a 2240 charger, charging 2x 12V 18Ah connected in series (so it makes a "24V 18Ah" for the motor, and this is also why they used a 24V charger)I'm really discovering all this set-up (it seems to be dead since even before the house was sold).

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 01, 2017, 05:34:04 pm
content: The simple answer is that if your charger can supply leakage plus consumption (remembering that charge efficiency is less than unity) it is adequate. The recommendations based on battery capacity are making some assumptions about consumption which may be much large than your couple times a week usage.Your existing charger was probably perfectly adequate when installed, and will be when your new batteries are in place. But over time the leakage current in the battery will rise, and eventually the charger will fall behind. It is not surprising that this has happened after 10 years which would be extraordinary life for a lead acid battery. A more powerful charger might delay the end a little, although quicker charging might degrade leakage faster too, cancelling the benefit of increased current availability.I think the real answer is to resign yourself to battery replacement every several years. If they make it 6-8 years you can feel you got excellent life.

author: drussell
author_rank: Super Contributor
timestamp: May 01, 2017, 05:34:12 pm
content: Quote from: CeD on May 01, 2017, 05:18:57 pmUnless the power goes out for days and someone is opening and closing the pool cover all the time or the charger gets disconnected and the batteries get fully drained or something, you're never going to be putting 18Ah back into the batteries. They should barely be discharged at all by a cover open or close cycle and just need a bit of a top-off from the charger.If the batteries everDOend up becoming fully discharged somehow,THENit will take a day and a half or so to charge them back up all the way at the 500ma trickle charge rate that charger can supply but I fail to see how that would be an issue in normal operation.

author: SeanB
author_rank: Super Contributor
timestamp: May 01, 2017, 06:01:59 pm
content: Typical use case of a SLA battery is gate operation, with it living almost the entire life on float charge, with only small draws due to gate operation. Similar to your application.I just had the gate motor battery die, and put in a temp one, and took the 3 year old deep cycle one out and, after some not so gentle work, got the sealed covers off, and saw it was simply dry. topped up the water, and charged overnight with the close to 70 year old charger I use for these, and it recovered somewhat voltage wise to 13.8V resting.Then, lacking a load tester, I did a DIY version, using some nichrome sealing element strip, around 10cm long, to do a 20 second discharge ( melted the wire after the 20 second mark, it was glowing white) and it did not drop below 12V on the terminals, so I guess the sulphation was not too bad.Left it another week, and also stuck the tops back on, and checked, and it was reading 12.6V, which was good enough, as I had not recharged it after the load test. Took it and put back in the separate battery box ( original used a 7AH cell, and there was no room in the housing for both the 7Ah battery and the charger unit, so separate it was, plus there had to be wiring in there for connecting stuff), and it can gas off there all it wants in the galvanised steel box.All I want is another year or so of operation out of it, and then I will not put in a special one, just a regular car battery, and see if there is any life difference, as the cheap automobile battery ( around half the price of the deep cycle) I just peel off the sticker and open the cells, to refill the water when needed. 90% of car batteries fail because they vent off water, dry out and sulphate, seems that checking the battery water is no longer encouraged, while it is a very cheap thing to do and will greatly increase battery lifetime.

author: Armadillo
author_rank: Super Contributor
timestamp: May 01, 2017, 06:03:41 pm
content: With whatever smart charger you purchased, your current configuration on permanent power hook up, the charger will always be charging in constant voltage/trickle charge mode as similar as conventional cheap charger.So save your money on buying those so call smart charger that is not suited for the application.