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Question on replacing Battery Separator


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#1 Kokopelli

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Posted 04 July 2021 - 11:05 AM

I have been upgrading the battery system in my Eagle.  I got a Renogy smart 100ah Lithium battery and a Vitron MPPT 100/20 charge controller.  The other evening I was checking things out and noticed a 2 amp draw on the system when I had nothing running.  Didn't have time to trouble shoot then, so looked at it the next morning.  The draw was .8 amps by then, and the battery had dropped to 88% overnight.  I isolated it to my Sure Power 1314 Battery Separator which was warm.  Took off the negative wire to it and the draw dropped to .1amps (the draw from the charge controller) and the separator cooled off.  Plugged it back in and the draw stayed at .1.  Started the truck, then turned it off and the draw was back to .8.  Unplugged the connector from the truck to camper and it dropped back to .1.  Overnight the battery only dropped to 99%.  So I need a new battery separator.

 

I searched through posts here on battery separators and read on line and am a bit confused on what I should replace it with.  Sounds like the Sure Power 1314 has a draw to it even when new.  Folks here recommend the Blue Sea 7622ML and the Blue Sea 7619 (if you don't need to fancier controls).  Then I read that using an ACR between a lithium house battery and the truck batter causes problems as they are not the same.  The Blue Sea 7622 has minimal draw - does the Blue Sea7619 also or does it draw more like the Sure Power 1314?  Can I use those with a Lithium house battery and a regular battery in the truck?  Do I have to do anything special?

 

I don't have a lot of power draw in my truck so may not need to charge from Solar/house to vehicle, but if it doesn't hurt anything, I'm fine with it.  I just want something simple I don't have to worry about, that won't take a lot of power, that will enable the truck to charge the house battery when driving, and that works well with the Renogy Lithium battery and Vitron controller.  Or I could just forget all the and only use the solar.

 

Thoughts?

Thanks!!

-Rick

 

 


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#2 rando

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Posted 04 July 2021 - 01:14 PM

I think you have figured out what is going on.  The Sure Power isolator uses a lot of power when on (0.8A) which is why it gets hot.  The resting voltage (~13.3V) of the lithium battery is high enough that once the Sure Power turns on it won't turn back off, even after the truck has started, so it will drain your lithium battery over time. 

 

You have 3 options to deal with this:

1. If you don't need charging from the truck (which you probably won't get much of anyway) then just disconnect the camper from the truck and let solar do its thing to keep the camper charged. 

2. Switch out the Sure Power for a Lithium specific battery separator.   This will work much like the Sure Power did but will correctly isolate the batteries when neither is charging.  You still will likely only get a few amps of charge from the truck, but it will allow the camper solar to keep the truck battery charged if you park outside.

3. Switch to a DC-DC charger  .  This will give you a consistent charge from the truck, but is expensive and may require you to replace the wiring between the truck and camper.   It also only goes one way, the truck will only charge the camper battery, the truck solar won't charge the truck battery.


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#3 fuzzymarindave

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Posted 04 July 2021 - 04:29 PM

I also had to ditch the Sure Power separator because of the switch to Lithium battery.  In fact I had to also ditch my solar charge controller and my Iota Power converter.  I ended up with a combo unit from Renogy.   It does trickle charge the truck battery when the camper battery is fully charged.     https://www.renogy.c...rger-with-mppt/

 


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#4 Vic Harder

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Posted 04 July 2021 - 06:05 PM

+1 to what has been said already.  You could also just put in a battery combiner/separator switch and manually connect the two systems when you want to, or as you already indicated, the BlueSea series of ACR include some with manual/remote switching.  There have been a few of those for sale here as people switch over to DCDC charging. 

 

The good thing is that you have located the source of the drain... it is both the inefficient 1314 as well as the voltage differential between your Lithium house battery and the lead acid truck battery.


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#5 Jon R

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Posted 04 July 2021 - 06:42 PM

I believe that all of the solutions offered so far, other than the dc to dc converter or permanent disconnection, fail to address the issue of high alternator load or fuse opening if you drive the truck with a deeply discharged lithium camper battery. The lithium battery in that state will take a lot of current, limited only by wire resistance, alternator output, or circuit protection. You want the current limiting that a dc to dc converter provides unless you disconnect from the truck charging system altogether.
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#6 LAWNMOWERMAN

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Posted 04 July 2021 - 06:51 PM

I have a Renogy 20 amp dc-dc charger and use a jumper wire system with the dc-dc charger off to charge my truck battery from solar when parked.


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#7 rando

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Posted 04 July 2021 - 06:56 PM

With the stock 10AWG wiring, this is unlikely to happen.  The wiring provides plenty of resistance to limit the current.   Even with 'upgraded' wiring it is unlikely to be an issue due to the length of the wire.   As an example, I installed 6AWG wiring from the alternator to camper, and even when under 50% SOC, the most current I see to the battery is ~10A and usually less than that. 

 

The key thing here is the length of the wire - even with 4AWG to the camper (30' round trip) you would be hard pressed to get more than 40A into the battery, unless your alternator voltage is much higher than normal.

 

I believe that all of the solutions offered so far, other than the dc to dc converter or permanent disconnection, fail to address the issue of high alternator load or fuse opening if you drive the truck with a deeply discharged lithium camper battery. The lithium battery in that state will take a lot of current, limited only by wire resistance, alternator output, or circuit protection. You want the current limiting that a dc to dc converter provides unless you disconnect from the truck charging system altogether.


Edited by rando, 04 July 2021 - 07:02 PM.

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#8 Kokopelli

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Posted 04 July 2021 - 08:02 PM

Thanks everyone - you guys are

awesome!!!

-Rick


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#9 Vic Harder

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Posted 05 July 2021 - 01:08 AM

With the stock 10AWG wiring, this is unlikely to happen.  The wiring provides plenty of resistance to limit the current.   Even with 'upgraded' wiring it is unlikely to be an issue due to the length of the wire.   As an example, I installed 6AWG wiring from the alternator to camper, and even when under 50% SOC, the most current I see to the battery is ~10A and usually less than that. 

 

The key thing here is the length of the wire - even with 4AWG to the camper (30' round trip) you would be hard pressed to get more than 40A into the battery, unless your alternator voltage is much higher than normal.

I have noted much the same, with 2AWG I was afraid of overheating my alternator, but have only seen 33A (battery was not discharged much though) from the truck to the camper.  I'm confused by that though, since I was sure the 200AH BBorn battery bank would suck down a LOT more... 


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#10 ntsqd

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Posted 05 July 2021 - 03:34 PM

When I built that system in our truck years ago I chose 6ga. conductors and chose 80A breakers. The alt is capable of 120A according to the mfg. I deliberately left some alt capacity to run the truck.

 

Batteries have an internal resistance, they limit their charge rate automagically. Just because you can supply 100A to the battery doesn't mean that it will charge at 100A. Now if you are using a super-capacitor instead of a battery, well, we're going to need a different approach......

 

Seems to me that it would be possible to tune the opening/closing voltage of a Blue Sea ACR with a resistor or two in the ground reference wire. I have not worked out if this would drive it up or down, but it would change it.


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