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Do all battery separators suck?

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#1 hunterh



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Posted 15 October 2021 - 05:04 AM

Yeah yeah, I know there are lots of other discussions about battery isolators out there, and I've read a ton, but can't figure out how to solve my problem: my battery won't properly charge from my truck's alternator.


I have a 2015 Fleet Shell model (no shore power), so I rely heavily on the battery charging from my truck's alternator. When I bought the camper, I noticed that the isolator would "click" on and off, and I wasn't getting much charge. Turns out the house battery was old and needed to be replaced. No biggie. I replaced the battery, and it appears that the same thing is happening. So, maybe my truck's battery is bad? Not the case, I tested it with a multimeter, and double checked by having it checked at an auto parts store. Maybe the 10AWG wire isn't big enough and the voltage drop is too high? Possibly... but FWC has repeatedly sworn by it. Bad battery isolator? I don't think so. The true culprit (so far as I can ascertain): Low voltage in the house battery.


For context, I'm running a two battery system in the camper with a Goal Zero Yeti 400 (https://www.goalzero...-power-station/) chained to a 12v deep cycle lead acid battery of the same size (https://www.goalzero...cement-battery/). Using this system, I can plug a solar panel into the Yeti 400 when the car is parked, and the chained battery is attached the the camper's ring terminal connectors. I run a domestic CFX3 50 IM fridge, which has pretty descent power draw. Currently, the goal zero battery is indicating that my batteries are 80% charged. Using a multimeter, I measured the chained battery at 12.4 volts (12.3 when the fridge is running). 


The stock Sure Power isolator says in the manual that it will detach the system (i.e. not charge) if the camper battery drops below 12.4-12.9 volts. This explains why it clicks on and off. It is trying to charge the camper battery, but the voltage is too low, so it cuts out. I saw a post where someone replaced their Sure Power isolator with a Blue Sea ML-ACR, which many people consider a superior product. However, the Blue Sea product STILL shuts off when the camper battery drops below 12.5V. The only reason this fix worked is because the ML-ACR includes an override switch to bypass the separator. 


So yes, for an additional cost and a bunch of frustrating installation labor, I could switch to the Blue Sea separator and have a fancy switch to force the batteries to charge while driving, but that seems pretty silly. I'm having a hard time understanding why the cutoff voltage is so high on all of these products. Based on voltage diagrams I've seen for typical 12V batteries, both of these isolators are only able to charge the camper batteries from 90 to 100 percent, but will not work if the battery drops below 90%. That seems absurd. Aren't these supposed to be deep cycle batteries after all? Shouldn't there be a product that can charge them up when they are more drained as long as the alternator is firing? Is there something I'm missing here? Thanks for your help!

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#2 DaveL


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Posted 15 October 2021 - 05:58 AM

Are you part of the Four Wheel Camper Owners group on Facebook?  If so, search on KP Pawley.  He's posted a lot on this issue, including an extensive post of this topic.  If your not a member, you should be.  It's a closed group that you request admission to.




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#3 PaulT


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Posted 15 October 2021 - 08:41 AM

Look at DC-DC chargers like those made by Victron, Sterling etc. They  will charge your camper battery at a 25 amp (or better) rate from the truck's alternator.  Read their requirements at the manufacturers web site for wire size. The 10 gauge that the FWC uses is really insufficient for the original purpose using the battery isolator.  You can remove the battery isolator and eliminate the issues related to its use.  


With lead acid batteries, you can bulk charge up to about 80% within a reasonable time. After that point, the lead acid battery enters  absorption mode that is a lower charge rate and much slower.


The automotive  battery charging system for the truck battery is not designed to fully charge the camper batteries. It is better referred to as a battery maintainer for the truck battery.


The DC-DC charger alters its operation to fully charge the camper battery. If you add solar charge controller and solar panels, that system will ensure that you can get to full charge. In addition, selecting a DC-DC charger that supports LiFePO4 batteries will ensure that you are ready if you choose to go that route for camper batteries in the future.


Read the extended posts on the site here by Vic, rando, and others to get a better understanding on what 

you need.



Edited by PaulT, 15 October 2021 - 08:43 AM.

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I thought getting old would take longer.

#4 heinphoto


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Posted 15 October 2021 - 02:09 PM

The problem is the 10 AWG wiring. We had ours replaced with 4 AWG and it made a huge difference in the current available to charge the camper batteries. 10 AWG is just too small for that length of run. We also replaced the Blue Sea ACR with a DC-DC converter, but that wasn't absolutely necessary. We just wanted to be able to drop in a lithium battery easily when our AGMs need to be replaced.

Edited by heinphoto, 15 October 2021 - 02:32 PM.

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#5 alano


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Posted 15 October 2021 - 02:43 PM

My experience is that the stock FWC separator worked - sorta. When house batteries are low and they need charging most, the separator valiantly prevents them from getting charged. Solar helps in that it can raise the voltage of the batteries enough to allow connection and a virtuous cycle results. Solar isn't always available when driving though. Smoke and clouds really cut into it and are regional rather than local issues like shadows from the terrain.


We first switched to thicker wire, a shorter run, and a DC-DC charger. AGM batteries lagging (2013 - 2021) so recently switched to lithium battery and integrated solar controller / DC-DC charger. Great setup.



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#6 astropuppy


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Posted 15 October 2021 - 02:49 PM

I'm super cheap and in a similar situation as you. Only instead of a "Goal Zero Yeti 400" we have a DIY Astro 600. 


When our lead batteries wear out, I intend to over battery the camper with as many Lithium AHR's as I can fit in the battery compartment of our Hawk Shell. Most likely I'll go the DIY battery route.


Until then, when the - lead - camper batteries get below 70% soc, I simply run our (Dometic 75L) refrigerator off the portable (Astro 600) overnight. This preserves the camper batteries for travel the next day. The next day: the portable unit gets charged in the truck cab and the camper solar panel charges the camper battery. If there's no sun; we rinse and repeat using the camper battery run the refrigerator during travel and the portable when camped. I can also unplug the camper batteries altogether and plug the camper directly into the portable. But then the BMS needs reset and its just a pain in general. 


If the camper battery gets really really low, I have a hobby charger to charge the camper batteries from the portable. Although tested, I have yet to exercise this option in the field. A 12v hobby charger will legitimately charge agm batteries and are relatively inexpensive.


Portable Power is just plain handy to have. The handiest for us is being to power our shower pump well away from the camper. I also find it handy to power our (portable) air compressor; Or, charge electronic devices while sitting in a lawn chair using them.


I pulled the fuse on our BlueSea battery separator a couple months ago.  Other than running/brake lights; I have no intentions of coupling the truck and camper electrical again. 


‚ÄčI hope this sheds some light on a different perspective of your situation. 

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#7 craig333


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Posted 15 October 2021 - 03:25 PM

Electrical has always been a weak point for FWC. Ten gauge wire was adequate way back when all you had to run was a couple lights and the fantastic fan. Why they continue to use this wire in todays campers is baffling. You don't have to use a separator. You can always control your charging manually. I use a marine battery switch in mine. 


Another issue may be your batteries aren't getting fully charged. If you're continually drawing them down and only partially recharging them they won't be very happy.

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#8 wicked1


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Posted 15 October 2021 - 03:58 PM

I'm late to the party, but as others have said, it's the 10 gauge wire.  Put in 4 or 6 and it will be OK.   It's odd they still use it, as it seems everyone has problems. 


Are you part of the Four Wheel Camper Owners group on Facebook?  If your not a member, you should be.  It's a closed group that you request admission to.

There is very much wrong w/ this.  Joining facebook is NEVER the answer. Putting technical support information in a closed group like that is very bad.   Don't support walling off information, please.  We are all entitled.  Not just those who agree to give up our privacy.    Ask the person to come here to help.  Then anyone can come and read the helpful information, even if they are not members. 

Edited by wicked1, 15 October 2021 - 03:58 PM.

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#9 Vic Harder

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Posted 15 October 2021 - 05:19 PM

What others have said... the voltage drop caused by the wires being too thin for the length of the run is mostly the issue.  Even with a DCDC charger, 6g is a good idea.


Also a good idea is to have a real battery monitor vs using voltage as a way of assessing the State of Charge.  Something like the Victron BMV 712.

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#10 ckent323


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Posted 15 October 2021 - 11:59 PM

I use the Blue Sea ACR in my boat and my camper.  Neither has a smart alternator. 

It is my opinion that when used in a well designed system (which includes proper wiring size) the Blue Sea ACRs work fine.  They are designed to protect the starter battery from being discharged (or overcharged) even if the house battery is discharged or overcharged.

However, if you try to use them in situations they are not really designed for (say between batteries with meaningfully different charge profiles), with undersized wiring or with smart alternators they may not perform as desired. 

As Vic said using a good voltage monitor such as a Victron BVM-712 is important.


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