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

[Gmanpaint]

Anybody use a 12V 140 Amp Smart Waterproof Dual Battery Isolator unit, to trickle charge a set of house batteries on a off road trailer?
I'm just wanting to charge the set of 110ah MAGM batteries as I'm traveling. Would the charge wire in the 7 pin harness be sufficient for this, or would I have to run a long 4awg/fuse, to the bumper/trailer/bat box?

This is the unit I have already. Yay, nay?

 

[kjp1969]

Would the charge wire in the 7 pin harness be sufficient for this, or would I have to run a long 4awg/fuse, to the bumper/trailer/bat box?

As I said above, the built-in charge circuit worked for me. I was really looking forward to someone with more knowledge to chime in, and hopefully someone will. I *suspect* that the 40a circuit might not charge as fast, but that may be a non-issue depending on your setup, how long your engine runs on any given trip, etc. For the sake of mocking up some wire and a 7-pin plug, why don't you give it a shot and see if it works? If it does, you'll save yourself a lot of trouble and cost. Not to mention avoiding an entirely new circuit and any problems that might accompany it.

 

[DiploStrat]

As I said above, the built-in charge circuit worked for me. I was really looking forward to someone with more knowledge to chime in, and hopefully someone will. I *suspect* that the 40a circuit might not charge as fast, but that may be a non-issue depending on your setup, how long your engine runs on any given trip, etc. For the sake of mocking up some wire and a 7-pin plug, why don't you give it a shot and see if it works? If it does, you'll save yourself a lot of trouble and cost. Not to mention avoiding an entirely new circuit and any problems that might accompany it.

Very hard, perhaps impossible, to reply without a lot more data.

-- What is the voltage of the Toyota's circuit? When you say it is a 40A circuit, is that because it has a 40A fuse? The real test is the gauge of wire.

-- "our Toyota Sequoia charged them just fine (or so I assume" Ahhh, that is the rub, without a battery monitor, it is hard for you to know what is going on and impossible for someone on the internet.

Soonoooo, if we are talking lead acid, and your Toyota is running at 13.9v, as many do, and the wire is about a 6 AWG (it could be much smaller), fused at 40A, and 25 feet long. (You can see that I am making a lot of assumptions here.)

-- You are delivering a maximum of about 13.1v at the battery. That is barely above the "full" charge voltage of 12.7v and actually below the most common float voltages of around 13.5v.

-- The charging rate will be very low and I suspect that your camper batteries will be chronically undercharged unless you top up with shore power regularly.

-- I would expect that the result will be reduced battery life, so you may have to replace the batteries early.

Sorry, the best I can offer.

 

[kjp1969]

Very hard, perhaps impossible, to reply without a lot more data.

-- What is the voltage of the Toyota's circuit? When you say it is a 40A circuit, is that because it has a 40A fuse? The real test is the gauge of wire.

-- "our Toyota Sequoia charged them just fine (or so I assume" Ahhh, that is the rub, without a battery monitor, it is hard for you to know what is going on and impossible for someone on the internet.

Soonoooo, if we are talking lead acid, and your Toyota is running at 13.9v, as many do, and the wire is about a 6 AWG (it could be much smaller), fused at 40A, and 25 feet long. (You can see that I am making a lot of assumptions here.)

-- You are delivering a maximum of about 13.1v at the battery. That is barely above the "full" charge voltage of 12.7v and actually below the most common float voltages of around 13.5v.

-- The charging rate will be very low and I suspect that your camper batteries will be chronically undercharged unless you top up with shore power regularly.

-- I would expect that the result will be reduced battery life, so you may have to replace the batteries early.

Sorry, the best I can offer.

This may all be true. Yes, I'm basing the "40amp" on the charging circuit fuse. I have no idea the gauge of the wire.

Chronically undercharged- possibly so; but we used shore power when available so this might not have been an issue.

So what can a non-engineer do to figure this out without simply throwing parts at the situation? Is it as simple as monitoring the voltage on the house battery while charging? Or while not charging?

 

[john61ct]

Get a cheap ammeter, figure out how to use it then come back

 

[DiploStrat]

Volts are interesting, but can be misleading, amps tell you what is happening in real time, and thus what to expect. In the end you need some form of serious battery monitor.

If you are bored, you will find three articles of use on this page: https://diplostrat.org/documents/

Specifically, "Watts Up," "Charging Up," and " Doubling Up."

None of this is hard, but it can become complex.

 

[joel.emal]

Okay so I need to read the basics of this thread. Want to add dual battery to our 4runner and would love the idea of running solar to it as well.

Sent from my SM-G965U using Tapatalk

 

[another_mike]

Okay so I need to read the basics of this thread. Want to add dual battery to our 4runner and would love the idea of running solar to it as well.

Sent from my SM-G965U using Tapatalk

Yep

 

[BritKLR]

For what it's worth, our 1995 Provan Tiger 4wd camper has had this basic factory installed system since new. It's still running the original 23 year old solenoid. We have one house battery and one truck battery and it has kept up with our systems. Thought about updating, but since it works great I'm just leaving it alone. Oh, I have added a 100 watt solar panel to supplement the Alt, but works great. Good luck!

 

[Wilbah]

I learn so much from threads like this and have literally nothing to add as far as technical expertise on wiring. You guys have it WAY over my head on this stuff. I really appreciate all the info people have posted here and especially evldave who has a knack for taking something complicated and making it idiot (*ahem* that'd be me) proof! Thanks!

One resource some might find helpful (at least if you're running GM equipment but for others who aren't I would look and see if you can find the same docs for your brand) is the upfitter manuals. GM produces these for all the various companies that make add on equipment and it has schematics for wiring of every system in the vehicles as well as documented layout measurements for the various body styles etc. Really helpful for doing planning of a buildout in your bed (how wide can those drawers be, will that whosywhatsit fit in the wheelwell, etc.) or in thinking, where can I find a hot "ON" wire in the rear loom to attach my camplights to for backing into a campsite.

Anyway just wanted to pass it on in case it helps.

Just pick your year here:

https://www.gmupfitter.com/pages/body-builder-manuals

Then pick from the chassis info or electrical. Really great info here for planning. Obviously you will have to test fit etc. but its good for starting planning anyway.

Just did some searches and here's the Ford version:

https://fordbbas.com/publications

And for RAM:

https://www.ramtrucks.com/ram-commercial/body-builders-guide.html

Have fun!

 

[continuecrushing]

as for charging/maintaining...can we use just one charger? I understand the batteries will be connected while charging, but is having two types and sizes of batteries an issue?

Or would it be best to charge individually?

Tried searching for tender or maintainer, couldn't find much.

 

[dwh]

as for charging/maintaining...can we use just one charger?

You can if the batteries are tied while you do it.

I understand the batteries will be connected while charging, but is having two types and sizes of batteries an issue?

Not as long as they are both lead-acid. There are issues tying lead-acid and lithium together.

Or would it be best to charge individually?

Not as long as they are both lead-acid.

Tried searching for tender or maintainer, couldn't find much.

Iota, Noco, Battery MINDer (different company than Battery Tender), Victron, Samlex, Xantrex, Sterling...bunches of others.

 

[continuecrushing]

Okay cool. Didn't know if different capacities would cause any issue. As for searching I just meant in this thread! Thanks for the quick reply.

You can if the batteries are tied while you do it.

Not as long as they are both lead-acid. There are issues tying lead-acid and lithium together.

Not as long as they are both lead-acid.

Iota, Noco, Battery MINDer (different company than Battery Tender), Victron, Samlex, Xantrex, Sterling...bunches of others.

 

[ohiobenz]

as for charging/maintaining...can we use just one charger? I understand the batteries will be connected while charging, but is having two types and sizes of batteries an issue?

Or would it be best to charge individually?

Tried searching for tender or maintainer, couldn't find much.

I just bought a charger/maintainer off Amazon.

https://www.amazon.com/Battery-Main...le+charger&dpPl=1&dpID=51J+CRir23L&ref=plSrch

 

[continuecrushing]

for those of you with batteries in the truck bed/far away-how are you protecting the cables?
I was looking at nylon sleeving, but didn't know if that would end up holding more debris.
Or just secure the wire against the frame well?