Deep cycle batteries - please help me fix!
 

Hi folks

I'm currently on a trans-Africa expedition. At the moment I've got 3 x 110 Amp/hour batteries in my truck, and after a year on the road, they're getting a little tired (ie: after many quite severe discharges they are not holding charge too well, or at least I get that impression - perhaps I'm just using too much charge and need to just increase the total Amp/hours capacity in my truck.) I'm in Nairobi in Kenya at the moment, and can get some new leisure batteries here.

My questions are thus:

1. If I buy some new batteries is it ok to connect them in parallel with the old batteries to eke out what life is left in the old batteries, or will the old batteries damage the new batteries, and therefore should I replace the old batteries in their entirety?

2. Is there a way to tell how much life is left in the old batteries? Will a battery outlet be able to tell me this? At what point should I consider replacing the old batteries?

3. If it's ok to add the new batteries in parallel with the old batteries, should I get new batteries with the same Amp/hour rating as my old batteries, or is it ok to mix and match Amp/hour ratings?

Many thanks in advance for your help!

Regards
Steve

(details on our journey if you're interested: www.overafrica.org)

Hi Steve-long time no speak (as it were!).

To answer your questions:
a) Don't wire the old and the new in together. The new will simply discharge into the old and knacker the new ones too. Bin the old and fit new ones. 300 amp/hr should be more than sufficient for what I remember of your set up. My truck has 270 and will run a compressor fridge full time even here in the UK-though not in the winter. Personally I wouldn't bother going to the extra expence of leisure batteries per se and would just use ordinary ones. The difference is that the plates on leisure batteries are thicker and will cope better with being over discharged and over charged. Provided you look after them a standard battery will do fine. I would suggest that you ensure that the new batteries are fully and properly charged before you fit them as a solar system may not be able to do this by itself

b) There may be. Some shops have a meter which is touched across the two terminals to see what the battery discharge rate is (causes a big spark) and this will tell you whether the battery is OK or not. But if the set up isn't holding its charge then at least one of the batteries is knackered and is pulling in charge from the others. This is because there will be a potential difference between them: i.e. one will be at a lower voltage than the other(s) My advice would be to replace the lot as for example if you replace 1 or even 2 because they're wired in parallel the new one will always be better than the old one(s) and the problem will persist, at least to some extent.

c) you can mix ampere hour ratings safely. As above, the key is the voltage.

Must have a look at your blog. The last time I looked you were in Angola!

Have fun

All the best Q

My system
 

Hi Q

Thanks for your response! Me thinks it must be 1 or more dead batteries. I'm sure, looking at the configuration of my system, it should be more than sufficient.

Here is a breakdown of the system, if that will help shed light on any issues.

Power producing

• 3 x 110Ah batteries
• 2 x 120W solar panels, producing only when sunny (which in Africa is almost all the time) +/-7A produced at midday, +/- 4A produced at 9AM and 5PM. Solar panels are controlled using a Steca PR10 30 charge regulator
• Truck alternator, producing 10A when truck is running (I have a 10A 24/12V converter connected to the truck alternator)
• Mains charging, producing only when at campsites providing electrical hookup

Power consuming

• National Luna freezer - 12V - 2.5Amps average running current. 1.53 - 2.6 amp/hour average power draw (I'd say on average it runs for 1 hour in every 2 hours, during the day)
• Sound system - 400W amplifier (100W x 4 channels), used +/-3 hours per day, when truck is not running
• Laptop computer - 12V 4.6A charger, used +/-3 hours per day
• Surflo pump - can draw 7A, but it only runs intermittently (ie: when a tap is opened – we don't use it for the shower a lot)
• LED lights - minimal consumption, only on for +/-4 hours per day

What do you think?

Thanks again
Steve
www.overafrica.org

It's really best to use identical batteries in parallel, because if you mix types then as soon as some power is drawn from the two different batteries, they won't be identical voltage and one will discharge into the other. You can use somewhat different batteries in series, i.e. in constructing a 24V system.
You will have difficulty finding deep cycle batteries in Angola, but it will be easier in Namibia and RSA.

Charlie

PS (10/15/09): Your solar panels produce only 7A max @ 12V? 120W panels should produce 7A EACH or 14A total; unless hooked in series for 24V (actually 35V regulated down to 28.8). My two 123W panels produce max 12-14A at >60 deg. N in the high summer of July. You may have one bad panel, check with a meter.

True Charlie but that's only really an issue if you use batteries of really different capacities e.g a 70 A/hr and a 170A/hr. I have used a decent 170 Varta and a 110 slightly dodgy Moroccan battery for 2 years now without problem.

Blimey Steve that's one hell of a sound system! Are you broadcasting to Africa? Seriously, I haven't done the calculations but your set up is much like mine so you shouldn't have a problem but that amplifier is going to use a massive amount of energy. I don't know if 400W is the consumption-it surely can't be but if it is-at 12V DC that would draw over 33 amps and really flatten any battery in next to no time. Over 3 hours (if 400W is the consumption) it would use 1200 watts whereas your fridge drawing 2.5 amps and on 12 hours out of 24 would only use 30Watts in a whole day. Can I suggest you try a day or 2 without the sounds (man!) and see what happens.

It's a good sound system! :)
I've managed to find the specs for the amp online, and it says the current drain, at the rated output, is 24A. That's still pretty power hungry isn't it?

Yep Steve. That may well be your problem. See how the batteries stand up after a few days off the music.

Steve
I asked a friend of mine who's up to speed with 'things electrical' for advice.
It seems like the battery/ies that start your truck are designed to deliver high amperage quickly but do not like going under about half their charge. They should not be deep cycle batteries.

For slower discharging batteries i.e deep cycle ( for fridges etc) these are designed to give less sudden amperage but for longer and don't mind being totally discharged.- and they are more expensive too-

You do not mention how your system is set up but it seems you may be using 3 of the same deep cycle ones and there is probably your problem.
And as for your hifi..... that's very power munching
Sounds like you may need new batteries and of the correct type.

For slower discharging batteries i.e deep cycle ( for fridges etc) these are designed to give less sudden amperage but for longer and don't mind being totally discharged.- and they are more expensive too-

As I understand it you shouldn't be discharging your deep cycle batteries fully if you want them to last. I'm no expert but from what I've read discharging to 2/3 or max 1/2 regularly will ensure a good lifetime for your deep cycles, any more than that and they'll suffer.

There's a piece here with some good info.

Bertrand, I have 2 12V truck starter batteries connected in series to provide 24V for starting the truck, and indeed they are designed to provide a high current for a short period of time. Then I have 3 12V leisure batteries (aka deep-cycle batteries) connected in parallel to provide 330 amp hours for the campervan side of things (ie: fridge, lights, pump, music etc). Deep cycle batteries, as you mentioned, are designed to provide a low current drain over a long period of time, which is what the campervan side of things will do. This is how the system is designed, and indeed should be designed.

As for deep-cycle batteries being happy with being completely discharged, this is incorrect. You will severely shorten your batteries lifetime if you completely discharge them. An example comparison of discharge depth versus life in cycles (a cycle being one charge/discharge cycle) for one type of deep-cycle battery is: 30% ~ 800, 50% ~ 400, 80% ~ 250, 100% ~ 100.

As for the amp, I've been doing some thinking on that: It would be interesting to know what current drain the amp causes in practice, coz we hardly ever listen to the music at full blast. I'd guess a far lower current drain, proportional to the percentage of max output we listen at?

My reasoning is this: I completed the entirety of the west coast of Africa (which is not at all set up for tourism, so there was practically never a chance to hook up to mains) with the 3 batteries I currently have. At one point, in Congo-Brazzaville, we got stuck for 2 weeks fighting with the Angolan embassy to get visas for Cabinda. During those 2 weeks we sat virtually all day every day in the truck, waiting for word from the Angolans, and the South African embassy who took up the fight for us (to no avail, but that's a long story... if you're interested, read here: OverAfrica - Congo-Brazzaville - the exodus)

Anyway, as you can imagine, we spent a lot of time listening to music while we twiddled our thumbs (probably in the order of 5 or 6 hours a day I'd guess.) There was a fair amount of rain around, being at the equator and just before the onset of the rainy season, so the solar panels weren't producing a huge amount of charge. At no point did our battery charge die. The solar panels were capable of keeping up with the current drain.

With that in mind, I'd say that perhaps the way we use the sound system is ok, and it's one or more batteries that have died. It would also probably be worthwhile getting a higher-current rated 24/12V converter for the truck's alternator, but not hugely necessary.

Any thoughts?

Thanks
Steve
OverAfrica - overland, over Africa

Steve- super website- enjoyed reading it- thank you

From what you say above I'm scratching my head here....all I can think of is that it's perhaps just time to replace your batteries with new ones - if so I would personally chose the same type, brand etc and replace them all together.
Other option as you say is going the higher-current rated 24/12V converter for the truck's alternator.
The minimalist in me also says to lose the hifi..... and go the Ipod and 'inMotion' IM9 route!:innocent:
It has a mains powered transformer but can run off 'C' batteries or better still on universal adapter so no need for mains- unit only needs 17 volts and 2.3Amps- way (too) loud, awesome sound !

Try and get in touch with Quintin who has a somewhat large truck! he might be able to go into details of how he has sorted his out.

I've been speaking to Collyn who wrote the Motorhome Electrics book (which I ingeniously left behind when we started the trip!)

His advice for checking the state of the individual batteries is this:
Fully charge the 3 batteries. Isolate and measure their individual voltage levels. After 30 mins re-measure their individual voltage levels. If there is a significant drop in voltage in one of the batteries (+0.2V) this is most likely the culprit. Now connect a load that draws about 1`0% of the battery Ah capacity (if 100 Ah use about 10 amps) to each battery in turn, and measure the voltage with the load connected after at least 2 hours. Batteries should really be within about 0.2V - if any battery has a voltage 0.5V lower than the others, that is the one that is stuffed.

I'm planning on doing this today... I'll report back with the results! Here's hoping I actually get results that make sense! :)

Hi all. Be intrigued to see what you discovered about the batteries Steve and I agree, in the absence of a 'proper' tester that is the way to go to find out how healthy each of your batteries is. The only problem with that method is that it assumes there is one perfectly healthy battery!

That said, your amp is really hammering your electrics. The fact that you're not turning the volume up is irrelevant because turning up the volume merely increases the pre-amp output voltage, i.e. the voltage that goes into your main amp. It won't affect the amount of power your amp is consuming. In other words no matter how low the volume is the amp will still be consuming 24 amps. I assume you have a standard stereo unit (radio/CD/MP3) plugged into a separate amp. I suspect that the reason you didn't have a problem down the West side is because the batteries were in good condition and (just) capable of satisfying your needs. As soon as they got a bit tired the load proved too much, exaccerbating the tired condition of the batteries.

I would be interested to know what voltage your batteries reach after a standard charge and without any load. Broadly anything over 12.7 volts would be regarded as fully charged. Similarly what is the voltage after say 2 hrs of 'the sounds'? Anything under 12 volts would be substancially discharged. I have seen a table somewhere which lists voltage with remaining battery capacity. Perhaps someone else can post it?

I'm not quite clear about you leisure side charging set up. Are you charging the leisure batteries (LBs) direct off the alternator simply using a voltage dropper and without regulating the alternator output? If so you could well be over-charging the LBs which might explain why they failed-if they have. I may be confused because I seem to recall you had a Sterling Battery-2-Battery charger. These are dead good because they vary the charge according to the state of charge of the LBs. Anyway, that's a side issue.....

Be interested in your results Steve

Q

Good point Q. I'll be sad to see my amp go, but for the sake of keeping the system in good health, it's gotta go. :( I've only got an iPod, no car radio or anything, so it's directly connected to the amp, I guess I'll just have to replace it with a lower power one.

For the testing side of things, here are my results:

I managed to get a hydrometer to test specific gravity. All I know about reading the results is that if it's in the "green section" (1.24), then the cell's ok, if not, then that's bad! :)

What I did is this:

Charged the batteries overnight, disconnected and measured the voltages.

Battery 1 had 12.81V
Battery 2 had 12.71V
Battery 3 had 12.73V

Specific gravity results:
Battery 1 (12.81V after charging)
Cell 1: 1.245
Cell 2: 1.24
Cell 3: 1.23
Cell 4: 1.245
Cell 5: 1.245
Cell 6: 1.25

Battery 2 (12.71V after charging)
Cell 1: 1.245
Cell 2: 1.24
Cell 3: 1.24
Cell 4: 1.245
Cell 5: 1.235
Cell 6: 1.245

Battery 3 (12.73V after charging)
Cell 1: 1.255
Cell 2: 1.25
Cell 3: 1.25
Cell 4: 1.255
Cell 5: 1.25
Cell 6: 1.255

Not sure what all this means, but I see batteries 1 and 2 both have a cell that is below 1.24.

Then I connected a handheld spotlight (not sure of the power rating, but since it's the same load for each battery I guess it should show if 1 battery is buggered over the others) for an hour to each battery in turn, and measured the voltage afterwards (with the load connected).

Battery 1 reads 12.25V (so a 0.56V drop)
Battery 2 reads 12.2V (so a 0.51V drop)
Battery 3 reads 12.2V (so a 0.53V drop)

I really don't know what these results mean... Battery 3 I thought would fare better, after the specific gravity check, but it's got pretty much the same voltage drop as the others.

Probably best to just change all 3, costly, but better than having them all die on me when I'm in the middle of the boondocks somewhere?!

As for the alternator charging side of things, I have a 15A switch-mode 24/12V converter. (Previously I said I had a 10A converter, but I made a mistake, it's actually 15A - which is still a bit low perhaps?) Not sure of the make, it has "AVDCDC15" written on it, Google reveals this is made by a company called "Amber Valley" but I can't find anything relevant online.

Any ideas at all?

Thanks for all the help
Steve

Your converter is from "K Po" I think.
K-PO - CB-Radios and Accessories -

http://www.everthammink.nl/images/00016556.JPG