Thread: Another 2nd battery bites the dust.

Hi mcrover, you should never discharge a battery for no reason, it just shortens the battery’s life span.

Have a look at the link below to the Trojan Battery web site. There’s some good info there that can easily be related to other brands of batteries.

Cheers



http://www.trojanbattery.com/Tech-Su...intenance.aspx

Originally Posted by drivesafe

<snip>
Once you disconnect the rear battery, and you only need to disconnect one terminal to get a reading, for safety reasons make sure it’s only the negative terminal. With the negative terminal disconnected, you should get a voltage reading at the rear battery’s positive terminal that is the same as the reading you will get at the cranking battery’s positive terminal after you have disconnected the rear battery’s neg terminal.

I wouldn’t be surprised if all the voltage readings rise after you disconnect the rear battery.

Cheers.

And of course if it does rise, then the problem is a poor (high resistance)connection somewhere, either in the wiring/earthing or inside the controller (faulty) rather than undersized cable, unless you can smell the insulation burning.

I'd try running a jumper lead between the negatives of the 2 batteries just to prove the point.

Hi Greame, the reason for the voltage rise is that the rear battery is so stuffed it is pulling the voltage down and by removing one of the terminals off the rear battery you will stop it drawing current and therefore the whole electrial system’s voltage levels will rise.

Cheers.

Pulled out the 2nd battery today. Still have 14.02v at front battery when the car is running. (14.04v at alternator). At the rear cable I had 13.86v.
Is this enough voltage drop to cause a problem?

I also hooked up a jumper lead between the negative of the 2 batteries and I then had only 0.01v voltage drop.

I will still replace + & - cables between the 2 batteries with 4G cable.

When I pulled everything out I also noticed one other thing. I don't have an SC-80 controller, I have a BI-80 controller.
Drivesafe, I will PM you today to organise getting an SC-80. I think the controller I have is stuffed because even with the car turned off for 1 hour, I am still getting voltage from the front battery, so it does not seem to be isolating.

Also, if you read this now, can you let me know whether it is better to have the controller close to the front battery or the rear battery?

ok, I did some more testing and found I was wrong about the chassis earth. The chassis is earthing fine, with only a 0.02v drop. It is the battery contoller that was causing the voltage drop. If I get rid of the controller, then with the wires that I already have in place I only get 0.02v drop between front and rear battery.

I was down talking to my auto elec and getting a new battery and I asked him about the wiring. He said I have 6G in their now and as long as I am not getting voltage drop and as long as I don't intend to uses the rear battery for cranking then the wire I have will be fine as it is well within the max amps you will get for charging only.

Does this make sense?

He also said that if I hook the 2nd battery up to a 240v battery charger every 3-4 months then I will get a much longer life out of the battery.

Hi Adam, first cab off the rank. There is no way to determine if the chassis is a good earth or not. Just putting a meter on it won’t tell you if you are going to have a problem once high currents are being used.

Next, as I have already posted, if you have 6B&S, 6AWG, 6G, it’s all the same and is 13.5mm2 cable BUT YOU MUST RUN A NEGATIVE AS WELL.

You obviously have a power supply problem and I suspect it is a lack of a good earth return BUT it could be something else but by running an earth, you are ruling out one possible cause.

Because of the problems you are having, I would recommend in your case that you fit the controller at the front. I know your old one was installed near your rear battery and normally this would not be a problem but for accurate operation of the controller, fit it up front.

As to whether putting a 240 volt charger on your battery is needed, again in your case it can’t hurt but I know a lot of people ( including myself ) that have never put a charger on their auxiliary battery and still get a good life span out of their batteries.

Cheers.

What is a good lifespan on batteries?

I have been getting about 2 years from the deep cycle battery.

I have run all the wiring and there is now negligable voltage drop down the back. (about 0.02v).
At the moment I have the 2 batteries linked together without a controler until I get a new one.

More questions. How does the D2 alternator work, inrelation to voltage sensing. I have been taking as many voltage readings as I can at different times and this is a pretty good average of what I get.

All votages at the alternator:

First thing in the morning - 14.50v
On start up after it has been driven but has rested for a while - 14.05v
After it has been driven for about 1/2 hour - 13.86v

Primary battery reading are all aprox 0.04v less than alternator

Rear battery reading are aprox 0.06v less than alternator.

PS. Did you get my PM Drivesafe?

Hi Adam, is the 13.86v at idle or with the revs up a bit because that is the absolute lowest you can charge a battery and this is most likely the reason for all you problems, furthermore, D2a discos usually run at anything up to 14.7 so it may pay you to have your reg checked.

And yes I got your PM and will answer it later.

Cheers.