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

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.

__________________
Unimog U500 w/Unicat

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.