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

[1v6pony]

Ok this leads me to a question, If the house battery is on a trailer do i have to run a ground all the way from the engine battery or can I use the trailer frame?
PS: I am so glad I found this post, I looked at the Ctek and other units and thought, Wow this is going to get expensive!!! Not any more I do not drink beer myself but it means I can buy more beer and bring to the party for others.

Frame/Body grounds by themselves are NEVER sufficient. You're relying on too many other things.

Always run a ground of equal gauge from one battery to the other.

 

[4RunAmok]

Ok this leads me to a question, If the house battery is on a trailer do i have to run a ground all the way from the engine battery or can I use the trailer frame?
PS: I am so glad I found this post, I looked at the Ctek and other units and thought, Wow this is going to get expensive!!! Not any more I do not drink beer myself but it means I can buy more beer and bring to the party for others.

I'm not an authority on trailers, but I believe that if you have a 7 pin trailer plug, there are positive and negative wires in that setup. Not the largest gauge wire, but is supposed to supply some higher current to the rear. Would I rely on it to charge a battery, probably not, if it's all I had, I wouldn't expect it to work very well. I would try to have my trailer mounted batteries either self-sufficient (solar) or put together my own (additional) anderson plug at the bumper to trailer, with 2 gauge wire from the charging system to the plug (fused at the charging source of course, probably an automatic charging relay as well) and run 2 gauge wire from the trailer battery to the plug (also fused at the trailer battery).

Others may do it differently.

 

[1v6pony]

Ok, I think I understand what you are saying.
this is my scenario, I am at the most only driving may be 3-7hr to camp, My stay is at the most 3 DAYS, ( weekend only, i have to work)
So is this set up really going to benefit me? it seams i do not drive long enough to charge the system.

Is sounds like I should just run a separate Agm battery and a solar panel on the trailer for charging... Is this correct?

I only have lights would like to charge phones and Kindle. down the road will add fridge , hot water on demand and pump.

 

[dwh]

Ok this leads me to a question, If the house battery is on a trailer do i have to run a ground all the way from the engine battery or can I use the trailer frame?

You can use the frame. Not optimal, but it'll work as long as the factory hot wire to the trailer plug is undersized wire - which it usually is. The problem is the connection between the trailer frame and the truck frame. That will either be crap, or totally non-existent. So you will need a ground wire between the trailer and the truck.

Fortunately, all trailer plugs do have a ground wire because without it, the lights wouldn't work.

UNfortunately, it's probably a pretty small wire sized to carry the load of the trailer lights.

So, as 4Run says, you're really a lot better off if you run some dedicated fat wire from the truck battery to the back of the truck, use a good solid plug connector and then do the same on the trailer.

But, it's not really required. From what I understand, most factory 7pin plugs have #10 wire to the hot pin, and I don't know, but I'd guess the ground wire is probably the same size, so yea, you could just ground the trailer battery to the frame.

The battery will charge. Eventually. It'll take longer though than if you used some dedicated fat wire.

 

[dwh]

So is this set up really going to benefit me? it seams i do not drive long enough to charge the system.

If there is a 7pin with a dedicated hot...well...it's there, might as well use it.

BUT, that dedicated hot might be hot full time - not just when the engine is running. In which case, you better not forget to unplug the trailer when you get to your campsite, or you'll be running the engine battery down along with the trailer battery.

Is sounds like I should just run a separate Agm battery and a solar panel on the trailer for charging... Is this correct?

For what you are doing - weekender only - you might not even need to charge until you get back home. Just depends on how much you draw down the battery while camping.

 

[1v6pony]

Great thanks for the info... Let me spend the money on the AGM battery, AGM charger ( will look at the one at Lowes posted) and all the other wiring stuff, fuse box, relays etc...
Shure learned a lot though...

 

[dwh]

Great thanks for the info... Let me spend the money on the AGM battery, AGM charger ( will look at the one at Lowes posted) and all the other wiring stuff, fuse box, relays etc...
Shure learned a lot though...

If you're talking about that Stanley charger that I mentioned - I actually did buy it, and it does work pretty good. I tested the de-sulphation (the real reason I bought it in the first place) on an old dead wasted battery, and it did improve the battery. Not enough to make the battery actually usable again, but it did improve it. So I'm convinced that de-sulphation does help. I'm no convinced that it does much more than help, but it does help.

I discovered something about that unit that isn't in the manual. According to the manual, you have to connect to battery first, then connect to shore power, then PUSH the charge button to make it start charging.

What I discovered is, if you hook it up and don't push the charge button, after like - I dunno maybe a minute - it will automatically go into charge mode on its own. I saw some vid on YouGooglusBoobusToobus where a guy had one, and he was talking about it and had not yet pushed the charge button - and it started charging which surprised the guy. So I tried it myself, and yea, it will start on its own if you forget to push the button.

I also found out that Baccus Global also makes the Black & Decker unit. And that the B&D and the Stanley actually have identical internals - they just have different shape/color plastic cases. Fricking corporate branding BS.


But, just FYI: If I was gonna do it over, I'd buy the 40a unit for 80 bucks instead of the 15a for 50 bucks. The most I've ever seen out of the 15a unit is 13.5a. Double that and add in a fudge factor, and you'll be right in the sweet spot for a new 100ah AGM.

 

[dwh]

But, just FYI: If I was gonna do it over, I'd buy the 40a unit for 80 bucks instead of the 15a for 50 bucks. The most I've ever seen out of the 15a unit is 13.5a. Double that and add in a fudge factor, and you'll be right in the sweet spot for a new 100ah AGM.

Okay, wait - lemme take that back.

Actually, I'd buy the 40a for use in the garage (Lowe's didn't have the 25a, so I dunno what it cost), which is where I use it.

But if I was gonna do the old "run a battery charger off the truck's inverter" trick, then I'd stay with the 15a, since it draws only 4a on the 120v side, so that's 480w max. A 400w inverter would probably run the thing just fine, and a 500w inverter certainly would. I haven't tried that...guess I should. But still, being able to run the charger off an inverter (only with the truck engine running of course!) is a handy trick when you need it.

The 6a unit for 30 bucks would definitely run from an inverter in a pinch, and would eventually get a battery recharged if plugged in in the garage (take at least 24 hours, but it would do it. However, the 6a unit doesn't have de-sulphation.

Looking at their site, I see they have a new one - an 8a unit. I was thinking about maybe getting the 6a unit to carry in the truck as a backup. It's not very big and can be hooked up through a cig lighter, so it I could fire the genny and use it to charge anyone else's battery if need be.

Looking at the manual, the 8a unit has selectable mode for motorcycle or vehicle mode. It also does not have de-sulphation. It also does not have the "quick charge to start engine" mode that the other units have. I tested that with the 15 unit, and it does work. Brought a battery up enough to start both my truck (left the lights on) and a buddy's car in 8 minutes (that's how long the quick start timer runs).

So for a backup, I'd choose the 6a, but it would also work in a garage as long as it was connected long enough. For running from an inverter, either the 6a, or the 15. For regular recharging a 100ah deep cycle in the garage, I wish I'd bought the 40a.

 

[lathamb]

I'm finishing this up on my 4th Gen 4 Runner tomorrow. Most difficult part was fabbing up the battery tray. I'll be using a Diehard Platinum Group 31M for the main battery, and a East Penn Intimidator Group 34 as the secondary. Thanks for posting this up!

 

[toyotech]

Heard its best to use the same battery for dual setup. Is this true??

I plan on doing this set up but could i use a switch to control the solenoid so I can engage the connection when I want.
Also could I just connect the ground side of house battery to the frame since I plan on having the house battery under the bed of the truck.
Thanks for the help

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[DiploStrat]

Heard its best to use the same battery for dual setup. Is this true??

Not necessarily. In fact, one of the reasons for installing an isolator of some sort, as opposed to merely tying several batteries in parallel, is to allow you to use a starter battery for your vehicle and a deep cycle battery for your camper loads. This is how my vehicle is set up.

 

[dwh]

Heard its best to use the same battery for dual setup. Is this true??

If they are tied into a full-time bank, then yes - identical type, size, age, etc.

But if they are only tied during charging, then it doesn't matter.

 

[toyotech]

I plan on doing this set up but could i use a switch to control the solenoid so I can engage the connection when I want???
Also could I just connect the ground side of house battery to the frame since I plan on having the house battery under the bed of the truck??
Thanks for the help

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Anyone? Also I got a free red top starter battery. Still holds a good charge. Ok for house battery? Mainly be power camp LED lights and charging iPhones and iPads. Along with other small devices ??


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[dwh]

I plan on doing this set up but could i use a switch to control the solenoid so I can engage the connection when I want.
Also could I just connect the ground side of house battery to the frame since I plan on having the house battery under the bed of the truck.

Sorry, was in a bit of a hurry on that last answer and totally muffed the other questions.

Sure you can add a switch. One of evldave's later graphics shows how. You're best bet is to wire it to ignition so it works automatically is you don't forget it, and then also add a switch that you can use to feed power to the solenoid when the ignition is off but you want to tie the batteries.

Yes you can use the frame for the ground. It's not optimal, but it will work. Might contribute to radio noise so if you're a radio guy, you might not like it.

 

[dwh]

BTW, I noticed Samlex has gotten into the RV/solar game:

http://samlexsolar.com/


One rather nifty thing I saw on their site was a smart battery isolator (split-charge type):

http://samlexsolar.com/rv-power-products/ProductDetail.aspx?pid=482