Battery Management
Submitted: Wednesday, Jan 06, 2010 at 22:08
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garrycol
My truck has two separate electrical systems. A 24v system to run the truck systems such as starting, lights, engine etc. The engine has a second 12v alternator that provides power to 12v batteries for other purposes as I choose. At present I just have an old 12v starter battery connected to it to suck up the charge. I want to develop this system to runs my fridge, other 12v requirements and on occasion a 12v electric winch.
I have decided to not go for deep cycle batteries (to much trouble and excessive cost) and have decided to install two heavy duty starter batteries of about 100-120 ah each. I accept the shorter life of the batteries. As I do not need to protect my main starter batteries from running down I do not need a dual battery system management system as such. These 12v batteries will be rigged in parallel but I will rig a switching system so that power can be drawn from either batteries or from both.
So to the question - do I need a management system to keep both these batteries charged equally or do I need just connect both direct to the alternator. Also I assume it is a good idea to have a low voltage cutout on the output to protect the batteries from going flat. Is there one that will automatically switch batteries if one gets low?
Thanks in advance.
Garry
Reply By:- Wednesday, Jan 06, 2010 at 23:07
Wednesday, Jan 06, 2010 at 23:07
garrycol,
Fridge most likely has its own low voltage cutout, and the winch doesn't need to be on a cutout as it could activate for no good reason. I'm not sure if the cutout device can even handle mega currents such as the winch's.
I'd rather go for a low voltage alarm than for a cutout switch.
But because they're starter batteries, this alarm voltage needs to be set higher than for a more standard deep cycle battery (same goes for cut out device if you opt to go for one).
I wouldn't bother to have them switched, just wire them in parallel.
Positive from alternator/regulator and loads to 'plus' of first battery, chassis ground to 'minus' second battery - to balance voltage drops in the parallel config.
If it was me, I'd switch the winch near the battery positive though as I don't like long unfused wires running to the switch box of the winch (unless the box can be wired near the battery of course).
Pity you didn't go the deep cycle way though, as it would have been a breeze to set up with their dedicated alternator/regulator. And you could have installed a third of your existing 'flooded' capacity in deep cycle which would have been cheaper amongst other things.
Best regards, batterymeister
AnswerID:
398010
Follow Up By: garrycol - Wednesday, Jan 06, 2010 at 23:57
Wednesday, Jan 06, 2010 at 23:57
Thanks for those great comments.
You lost me a bit here though "Pity you didn't go the deep cycle way though, as it would have been a breeze to set up with their dedicated alternator/regulator. And you could have installed a third of your existing 'flooded' capacity in deep cycle which would have been cheaper amongst other things."
When you talk about dedicated alternator/regulator - I assume you mean the trucks 12v alternator?
Can you explain a little more this statement - "And you could have installed a third of your existing 'flooded' capacity in deep cycle which would have been cheaper amongst other things."
The main reason I do not want deep cycle is the cost and the hassle looking after them - there are heaps of threads about people killing them and needing special chargers. People who have stayed with normal batteries have had no issues and seem to get good life for much less cost.
Cheers
Garry
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Reply By:- Thursday, Jan 07, 2010 at 00:41
Thursday, Jan 07, 2010 at 00:41
Yes, the 12V alternator you feed your two big flooded batteries with.
Considering you get hundreds of 'deep cycles' e.g. Depth Of Discharge being 80% to 90% from a VRLA AGM deep cycle battery, and only a few dozens or so from flooded ones, you only want to discharge your flooded ones to about 25% to get similar cycle life from them.
Doing the numbers for your flooded batteries' capacity of about 220Ah, the result is 55Ah.
If you
shop around for a 75Ah VRLA AGM deep cycle battery, you'll most likely find that these are quite a bit cheaper than the two flooded biggies of yours.
As for charging: if you look at the AGMs float charge voltage requirement of 13.6V you can match this to your alternator's output voltage: if alternator sits on 14V: use an isolation diode with a forward voltage drop of 0.4V, if alternator sits on 14.3V, use a diode with a drop of 0.7V, if alternator sits on 13.8V, don't bother with diodes and connect your AGM battery directly to the alternator.
If your 12V alternator has an external regulator, you can buy a dedicated VRLA AGM charger/regulator for it and forget about the isolation diodes. This device allows for three stage charging of your deep cycle AGM (similar to a high rated multistage mains charger).
The advantage over 'normal' alternator float charging is that you can dramatically shorten the charging times as your charger/regulator now allows for 14.4/14.7V boost charging...
A good auto sparky should be able to help you out if required.
Best, batterymeister
AnswerID:
398020