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Old 04-20-2015, 12:19 AM   #1
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Replacing Starting Batteries with Deep Cycles

Pretty obvious what I want to talk about here.

My bus has two separate electrical systems:

12V chassis/starting system running my interior 12v lighting, the water pump, and a couple small fans. This is charged off a 100 Watt (might be upgraded 225 watt) solar panel.

and

24V house system running my 120V stuff charged off 1200 watts of panels

The starting batteries in my bus are in great shape and less than a year old. But I am considering swapping them out for either two or three deep-cycle lead-acid batteries since now I use them as storage for my 12v system and stuff.

I dont think I will have any problems, but I'm just wondering what everyone thinks about using 2 or three deep cycle batteries for the 12v side on my bus, including the duties of starting the engine.... I dont think I'll have a hard time getting enough amps out of a couple t105's (6V) or 3 T-1275 (12V)....

Its not like im tryna crank a Detroit at -15 in the snow for a few minutes.

I've used and seen used many single-battery equipped DT466's that start just fine.

What are you guys using for your 12V setups?
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Old 04-20-2015, 06:43 AM   #2
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i know they make a 12v marine deep cycle/ starting battery. not sure if a deep cycle battery would turn it over, or if it would hurt the batteries. since there new what about adding 1 or 2 more of the same type, 100 watts is plenty to keep them charged
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Old 04-20-2015, 10:17 AM   #3
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Quote:
Originally Posted by charles_m View Post
The starting batteries in my bus are in great shape and less than a year old. But I am considering swapping them out for either two or three deep-cycle lead-acid batteries since now I use them as storage for my 12v system and stuff.
I'd be very surprised to see 2x T105s turn over a big 6 cylinder diesel engine. If they were able to turn it, I wouldn't expect them to do the job for long due to the voltage drop.

I killed the battery in our Subaru Legacy last summer and, luckily, had a fully charged 12v deep-cycle battery in the back of the car. I used the jumper cables to connect the starter battery to the deep cycle battery, left them for 10 minutes and tried to crank the car. Just a click. It didn't turn over at all. After leaving it for 30 minutes it had transferred enough to the starter battery to crank the engine. That was a 2.2l gas engine. The starter for a diesel will pull many times the amps to get the engine spinning.

Similarly, I have boosted the bus engine twice by connecting the house batteries to the starter batteries, letting it sit for 15-20 minutes then turning the engine over. That works just fine.

Do you have the specs for the batteries you intend to use? Perhaps there is a listed maximum amp draw. I would guess that you'd need a burst of 300-400 amps to get the starter spinning.
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Old 04-20-2015, 02:54 PM   #4
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Maybe Ill keep my two starting batteries on their own branch and use a couple deep cycle batteries when Im parked and then tie into the starting batteries to start and drive.

I am finding myself using the 12v lights and accessories more than I thought but my main solar bank is 24v. I like tge idea of having the redundancy of two independent systems.
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Old 04-20-2015, 05:02 PM   #5
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I'd be very surprised to see 2x T105s turn over a big 6 cylinder diesel engine. If they were able to turn it, I wouldn't expect them to do the job for long due to the voltage drop.
.
Trojan T105's are "rated" at 1000 amps. I think that by rated they mean at what point the battery will self destruct. The minimum would be 4 t195's if you value your batteries.

I think that you would be better off using 3 mid range 12 volt deep cycles. Not quite Trojans but a step above Walmart.

Or even better, leave your starting bank and add a separate 12 volt aux. bank.
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Old 04-20-2015, 05:31 PM   #6
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Quote:
Originally Posted by charles_m View Post
Maybe Ill keep my two starting batteries on their own branch and use a couple deep cycle batteries when Im parked and then tie into the starting batteries to start and drive.

I am finding myself using the 12v lights and accessories more than I thought but my main solar bank is 24v. I like tge idea of having the redundancy of two independent systems.
Somehow I missed earlier that 12v loads vs 24v house battery seems to be the main problem. If you haven't already, maybe you could consider a dc-dc converter to step the 24v house batteries down to 12v for your various loads. Not knowing anything about just how much load we're talking... here are several options that are comparable to the cost of one deep cycle battery. I don't know whether I'll use any of those, exactly, but this is the direction I'll be headed when I'm ready to sink money into batteries for mine (24v or 48v battery bank with step-down converter(s) as needed).

By the way, some of those converters can actually be used as a battery charger, too -- you could wire one of these from the 24v system to the 12v system so that energy from the big solar array is fed to keep the 12v batteries charged too.
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