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Old 09-07-2020, 07:41 PM   #1
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Hellllllllpppppp! Lol

I'm converting a mini bus with a Chevy chassis. I want to add a battery isolator to run my 12volt side of my power when not plugged in. I don't want to add solar. Why??? I have no clue. Lol here's my question. Can I run 2 batteries in parallel on the aux side of the isolator?? I don't see why I can't but I'm not 100% sure. This is going to be more of a tailgating conversion.

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Old 09-07-2020, 08:54 PM   #2
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A single 12V battery is a series string of 6 cells.

A whole bunch of batteries together is just one big battery.

So, yes
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Old 09-07-2020, 09:21 PM   #3
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Boaters use a selector switch to choose which battery powers the load or you can disconnect them both or tie them together.

https://www.fredwarner.net/product/b...ccc312b79bc5b7

You can charge your camping batteries when driving, use only your camping batteries to save your starting battery for starting, and connect only your starting battery for starting.
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Old 09-08-2020, 02:41 AM   #4
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Year: 2002
Coachwork: Thomas Built Bus
Chassis: Freightliner FS65
Engine: Caterpillar 3126E Diesel
Rated Cap: 71 Passenger- 30,000 lbs.
We have two battery banks, a house bank and a chassis bank. We have a battery isolation relay that hooks the two banks together when I flip a switch. We have the chassis battery hooked up to the stock engine alternator. We have the inverter/charger hooked up to the house battery.


While driving, the stock alternator will always keep the chassis battery charged up. When the battery isolator switch is turned on, the stock alternator will charge both battery banks.


When on shore power, the inverter/charger will always keep the house battery charged up. Again, when the battery isolator switch is turned on, the inverter/charger will charge both battery banks.


When starting the engine, I turn off the isolator. If the engine starts to slow down too much, I can always flip the isolator switch and get an instant jump.


Note: I also have a second alternator to charge the house battery while running. If the isolator switch is off, the house alternator charges the house battery and the stock alternator charges the chassis battery. If the isolation switch is turned on, both alternators work together to charge both batteries. I did not include this in my initial part of this post because a second alternator is not needed for the battery isolation relay to work as you describe you want it to work. In our use case, we needed a second alternator to power our air conditioner while driving since our bus did not come with factory air.
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Old 09-08-2020, 10:58 AM   #5
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I agree with what Native said. I'd only add that if you are using deep cycle lead acid batteries for your house batteries and charging them with the vehicle alternator their life span will be considerably shortened (per Trojan mfg). Furthermore, if you use all start batteries you will not get as much power over time before the start batteries have run out of available power.

A better solution to charging deep cycle house batteries is via a battery to battery charger. This allows you to use the alternator to charge all batteries in the correct way for their design and provide the greatest longevity for both types of batteries.

Whichever method you choose be certain that your vehicle's alternator produces enough power to meet your charging needs without having to run flat out 100% of the time--it'll fry your alternator. The rule of thumb I was taught a million years ago is that an alternator should not be tasked to run at over 85% load except in short bursts like when rapidly recharging the start battery after start up.
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Old 09-08-2020, 11:17 AM   #6
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im 4 years in with my AGM interstate group 31's. and no noticeable loss of capacity.. alternator charged all along the way
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Old 09-08-2020, 11:55 AM   #7
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I have two batteries in parallel for the chassis battery-that is stock for my bus. I added two batteries in parallel for house batteries, and put them on the other side of an isolator. Search 'Battery Doctor' on Amazon for a selection of these isolators. They charge the house batteries when the vehicle is running but isolate when it is not. Press a button and they are instant jump start batteries. No need to remember switching things for normal operation though, it is all automatic. Maybe yours is the same.

The system seems to work fine.

I don't have solar (yet). I'm expecting the two house batteries to be enough for a few days off grid, even if we're not moving.
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Old 09-08-2020, 05:12 PM   #8
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I charge my batteries off the alternator too while driving. Works well, but what I do find is that the alternator does not really top them off fully, and deep cycle batteries do like to be topped off. I do have solar and that will top them off after driving and bring them to 100 %. 80% is about as high as they get from the alternator.



As far as battery life both my previous campers did not have solar and charged only from the alternator through a battery isolater. So far the batteries for the bus are holding up much better and longer then ever before, and I believe that having the solar to bring them up properly, as well as keep them from getting as discharged as they were in the camper is making the difference.
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Old 09-09-2020, 07:37 PM   #9
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Thanx for all the info. It was a big help.
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