Understanding Battery separators versus battery isolators, for charging via a car alternator.

[DanB.]

*Original post in Modification thread.


Hi,

I apologize if questions like this has been asked before. But I didn’t really find something that seemed to best answer the particular situation I am working on in my own small set up and car.

I have a Subaru outback and some accessories that runoff of a deep cycle battery that I can either charge using a standard wall charger or an 80 W solar panel.

Obviously and 80 W solar panel is a little bit problematic as I live in Washington state.

And as we all know sun can be a little unreliable and the trees. However the 80 W panel is fully capable of running my 50 W fridge cooler, and still supplying a little bit extra for charging the battery; but it would take an eternity in that setting. Also, can’t really use the panels while driving.

I used my 400wt inverter to charge of the wall charger, but that didn’t work and I had a repair to make...

So I am trying to determine a good and safe way to set up a battery isolation system where I can safely charge the deep cycle battery in the back of my car, without putting any risk on either the alternator or car battery and/or intern the deep cycle.

When I call places like camping world and auto-parts stores they seem thoroughly confused with the concept of what I’m trying to do. I know it can’t be that unheard of, I’ve seen it done in RV and where others are showing off rigs, both custom and etc

Probably longer winded than it needed to be but I would appreciate any expertise that anybody might have. if you have a recommendation of product, that would help.

 

[DanB.]

Would something more like the image below possibly be more productive as an avenue to solve this problem. Using a battery separator circuit with built-in logic?

 

[DanB.]

Can this method also be pretty reliable as far as usable charge after several hours of driving, and also being supplemented with a solar panel.

 

[Martyn]

i Think you need to look at dual battery charging systems. Basically a unit that senses the charge on the starter and auxiliary battery and then automatically switches the charge from one battery to the other. National Luna makes a good unit, go to equipt1.com to see that unit. BlueSea makes some excellent marine units that does a similar thing, I think it’s their MCR units. Red arc also makes a unit that will work with flooded, AGM and lithium combination.

 

[DanB.]

i Think you need to look at dual battery charging systems. Basically a unit that senses the charge on the starter and auxiliary battery and then automatically switches the charge from one battery to the other. National Luna makes a good unit, go to equipt1.com to see that unit. BlueSea makes some excellent marine units that does a similar thing, I think it’s their MCR units. Red arc also makes a unit that will work with flooded, AGM and lithium combination.

My understanding is that a battery separator does exactly that and is much better and preserving the overall life of a battery while still remaining one way. Both a battery separator and a battery isolator will charge both, But the separator uses a solenoid switch and logic board, whereas the battery isolator just uses a Capacitor or a group of capacitors.

what I’m hoping to find out is if people are using either of the two in which one they like better and why. There’s a lot of things out there that are sort of cheap fixes for the problem, but they either cost the life of the battery or have potential risk in other areas.

does anybody have any outfitters they are familiar, who work very specifically with this sort of stuff and might be able to answer questions via phone?

 

[rayra]

How to make a cheap isolated dual-battery setup for $50

So there are a lot of kits you can buy to have truly isolated dual-battery setups. Those are VERY NICE kits. They are also very expensive. I try and replicate those kits without spending as much money, while still having a similar level of quality and/or reliability. There are constantly...

expeditionportal.com

A $40 200A solenoid which is triggered by a low amp keyed accessory circuit will do everything you want to put a bulk charge on your second battery.*

There's some design vagaries depending on whether your vehicle puts out 14.1-14.2V or 14.6-14.7 in normal charging operation, and if your aux battery needs that higher voltage to charge properly. And IIRC you General Mod topic on the same thing you mentioned solar. In which case your solar should be putting out that higher voltage / be matched to your aux battery type. So your vehicle's factory charging setup may be sufficient.

*I am using this in my Suburban, for a couple years. works great. Along with many other power mods, rooftop solar

 

[evldave]

A few thoughts:

Separators typically use a diode, which has a 0.7v drop, meaning you are actually not charging at full voltage.

Using the details in the linked thread to set up an isolator, you will get full voltage using an isolator.

If you are storing the battery in an enclosed space (trunk, cab, etc) it is best to used a sealed battery because of outgasing.

80w in Washington will be fine to charge a baterry during the day, but likely won't run your fridge. I have a 100w panel and it can keep the fridge running on sunny days but doesn't have enough extra current to also charge the battery fully except JULY/AUGUST.

 

[Laps]

Ironically, there is a Redarc advertisement at the top of this page.

 

[Martinjmpr]

A DC-DC charger would do exactly what you want to do without the need to run heavy 1AWG or 0AWG cables.

Here's the writeup on the one I installed on my F-150 last weekend. Should work in any vehicle. Biggest issue is going to be getting a pair of 8AWG wires from the battery compartment to the trunk. If you can do that, everything else is easy.

Installing Renogy DC-DC charger in 2018 F-150

Posting this for anyone who might be interested in doing something similar. Background: The idea behind this came from my previous vehicle, a 2004 Suburban. When we camp we use an Indel-B TB 41 refrigerator and in the past we've had "issues" with it discharging the battery enough to cause...

www.expeditionportal.com

 

[rayra]

I'd really like to find the hidden crypt of the 'overlander' necromancer spreading / promoting this DC-DC charging nonsense and drive a wooden stake thru its heart.
It's Cargo Cult nonsense, another expensive solution foisted on top of folks that buy AGM battery tech for vehicles that won't natively support it. And lining up to pay premium dollar for the privilege.

I can't see the use case for these things for a House battery. Other than the need to charge an AGM to the Nth degree. Would it not be the case that you'd draw down that 'house' battery camping somewhere for a couple days and then want to shift camp to a new location, during which time you are driving. And instead of the 100A+ you could be putting into that Aux battery from your vehicle alternator, you are instead limited to the ~20A (or 50A or whatever) that you've restricted the Aux to receiving, via a DC-DC charger that cost you 5-7x more than a dumb combiner solenoid. And if your drive isn't long enough to your next camp, you arrive with your House battery still partially depleted.
Wouldn't a better solution to be a proper AC/DC conditioning charger for your AGM / house when not camping, and bulk-charge it with your vehicle charging system during your short outings? Or even more useful, vehicle solar with a charge controller that will properly top off that AGM battery, on top of the bulk charge provided by your vehicle?

If it's a one-way connection, you only want to dump power into a House and you specifically DON'T want the combined output of both batteries for say a winching situation, then all you need is an 8ga or 4ga wire tying your AGM/House to your vehicle's normal charging system to bulk-feed it. A few feet of wire and the cheap solenoid, vs the expense and limitation of a DC-DC device.

 

[Martinjmpr]

I'd really like to find the hidden crypt of the 'overlander' necromancer spreading / promoting this DC-DC charging nonsense and drive a wooden stake thru its heart.
It's Cargo Cult nonsense, another expensive solution foisted on top of folks that buy AGM battery tech for vehicles that won't natively support it. And lining up to pay premium dollar for the privilege.

I don't understand why you get so worked up when someone chooses a solution that's different than the one you chose. Just because a dual battery works for you doesn't mean it will work for everyone. In the OP's case he doesn't need a permanent 2nd battery and given that he has a Subaru he likely doesn't have space for one. This is exactly where the DC-DC charger works best.

You've also grossly exaggerated the cost delta between a DC-DC charger and a 2nd battery/solenoid combo. In terms of cost the difference between a 20a DC-DC charger (about $110 - $120) and a solenoid (~$50) plus the cost of 10 - 15' of heavy 0 or 1 AWG cable that would be needed for a dual battery setup so even at Amazon prices of roughly $2.50/foot you're talking another $50 just in cable (to say nothing of the need for either a nice set of heavy duty crimpers or the ability to solder a terminal onto that heavy cable.)

20A of charge is less than 100A but it's likely more than adequate to keep a battery charged up on a few hours of driving.

 

[rayra]

I don't understand why you get so worked up when someone chooses a solution that's different than the one you chose. Just because a dual battery works for you doesn't mean it will work for everyone. In the OP's case he doesn't need a permanent 2nd battery and given that he has a Subaru he likely doesn't have space for one. This is exactly where the DC-DC charger works best.

You've also grossly exaggerated the cost delta between a DC-DC charger and a 2nd battery/solenoid combo. In terms of cost the difference between a 20a DC-DC charger (about $110 - $120) and a solenoid (~$50) plus the cost of 10 - 15' of heavy 0 or 1 AWG cable that would be needed for a dual battery setup so even at Amazon prices of roughly $2.50/foot you're talking another $50 just in cable (to say nothing of the need for either a nice set of heavy duty crimpers or the ability to solder a terminal onto that heavy cable.)

20A of charge is less than 100A but it's likely more than adequate to keep a battery charged up on a few hours of driving.

I'm not 'worked up'. I'm expressing an opinion with some vigor and some humor. And I never said anyone else needed to use 1/0 to charge a friggin battery. My use of such ehavy cablign is predicated on wanting to use a large winch at the rear of my vehicle. I have never said it was necessary for anything else. I've taken advantage of having that heavy cabling in place to use it as a backbone for a lot of other things. And again have never said it was necessary or required for anybody or anything else.

If you are just routing juice to a second battery that will not be DIScharged in conjunction with your starter battery, all your need is a wire rated to handle your alternator output. And some sort of combiner / disconnect that preferably doesn't rely on a human to remember triggering it.

I just don't see what a DC-DC charger adds, other than addressing a problem brought on my using battery techs that need higher charging voltages than most factory electrical systems will apply. And all newer PWM and MPPT solar charge controllers will do what the DC-DC does. And by happenstance my aftermarket high-amp-output alternator not only puts out high amps but also at 14.6-14.7V. So I'm left wondering what a DC-DC would bring to the party and it seems nothing, but higher expense and throttling the charge rate to my Aux / House battery.

Somewhere along the way the idea of having a 'house' battery as a way to separate loads from the vehicle starter battery is getting forgotten / violated, by connecting a DC-DC charger to the starter battery. Just you watch, very soon there will be people asking / talking about a means to keep the DC-DC hot and running when the key / engine is off. Producing the very situation that a 'House' battery is supposed to be avoiding. Sucking juice out of the Starter battery while camped. And the next solution will be a more costly DC-DC charger that will detect lowered voltage on the Starter battery side. And folks will gladly pay hundred$ for a bandaid on a bandaid on a battery tech that isn't suited for their vehicle's factory charging system.

 

[Buddha.]

I'm not 'worked up'. I'm expressing an opinion with some vigor and some humor. And I never said anyone else needed to use 1/0 to charge a friggin battery. My use of such ehavy cablign is predicated on wanting to use a large winch at the rear of my vehicle. I have never said it was necessary for anything else. I've taken advantage of having that heavy cabling in place to use it as a backbone for a lot of other things. And again have never said it was necessary or required for anybody or anything else.

If you are just routing juice to a second battery that will not be DIScharged in conjunction with your starter battery, all your need is a wire rated to handle your alternator output. And some sort of combiner / disconnect that preferably doesn't rely on a human to remember triggering it.

I just don't see what a DC-DC charger adds, other than addressing a problem brought on my using battery techs that need higher charging voltages than most factory electrical systems will apply. And all newer PWM and MPPT solar charge controllers will do what the DC-DC does. And by happenstance my aftermarket high-amp-output alternator not only puts out high amps but also at 14.6-14.7V. So I'm left wondering what a DC-DC would bring to the party and it seems nothing, but higher expense and throttling the charge rate to my Aux / House battery.

Somewhere along the way the idea of having a 'house' battery as a way to separate loads from the vehicle starter battery is getting forgotten / violated, by connecting a DC-DC charger to the starter battery. Just you watch, very soon there will be people asking / talking about a means to keep the DC-DC hot and running when the key / engine is off. Producing the very situation that a 'House' battery is supposed to be avoiding. Sucking juice out of the Starter battery while camped. And the next solution will be a more costly DC-DC charger that will detect lowered voltage on the Starter battery side. And folks will gladly pay hundred$ for a bandaid on a bandaid on a battery tech that isn't suited for their vehicle's factory charging system.

Our GM trucks put out that much voltage but those Japanese cars don’t. I think 13.8 is the norm, and then there’s voltage drop and losses at the connectors. The point about the DC to DC charger reducing the output from 100amps to the 20/40 the charger puts out is kinda moot. The battery isn’t gonna take 100amps of charge anyway.
The cheap solenoid is still a decent option for OP, his AGM house battery might have somewhat reduced life from not getting as high a voltage for as long as it wants. If the battery is sitting in his garage most of the time though he could just leave it on a good trickle charger and it wouldn’t matter.

 

[DanB.]

I am reading all opinion shared here, but I would like to remind people that while yes I do charge the battery at home on a trickle charger, the goal is how to charge it went out in BLM land for two weeks not having access to any type of electric grid other than my solar panel which will help mitigate some of the depletion during the day, but in periods of time where I am doing extensive driving the solar panel does not come and play at all, so how do I get around charging it efficiently and effectively during that time.

 

[evldave]

I am reading all opinion shared here, but I would like to remind people that while yes I do charge the battery at home on a trickle charger, the goal is how to charge it went out in BLM land for two weeks not having access to any type of electric grid other than my solar panel which will help mitigate some of the depletion during the day, but in periods of time where I am doing extensive driving the solar panel does not come and play at all, so how do I get around charging it efficiently and effectively during that time.

Use the link I provided to set up an isolated battery setup the will charge your house battery while driving as best as possible. You can certainly buy a kit to make it easier or build your own (per instructions in the thread).