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

[TLC Norway]

Yep, a vsr and a manual switch should do it.

Sent from my SM-G388F using Tapatalk

 

[moineau11]

I have a dual battery TMAX system but it doesn't work anymore, I think the relay is dead.
Which kind of relay can I use to replace it ? I think it's 250 ampères...

 

[4RunAmok]

A voltage sensing relay is the answer. A manual switch is not. If your solar is low performing or stops performing, and you've manually connected your batteries, they'll both drain.

One other trick would be to source power for your jump start switch from the aux battery. You could source it from both batteries using a double pole switch, so then it won't matter which battery has power, the switch will still work.

The solid solution to the charging issue is to replace the solenoid with a Blue Sea 7622 ACR. This will combine the batteries when there is charging sensed from other side of the ACR.

 

[dlichterman]

A voltage sensing relay is the answer. A manual switch is not. If your solar is low performing or stops performing, and you've manually connected your batteries, they'll both drain.

One other trick would be to source power for your jump start switch from the aux battery. You could source it from both batteries using a double pole switch, so then it won't matter which battery has power, the switch will still work.

The solid solution to the charging issue is to replace the solenoid with a Blue Sea 7622 ACR. This will combine the batteries when there is charging sensed from other side of the ACR.

The idea was a switch on the VSR so that it is only doing the reverse charge when you want it to as to not have it connected in normal driving as it would be a smaller gauge wire. Wish that blue sea 7622 wasn't so expensive haha.

 

[4RunAmok]

The idea was a switch on the VSR so that it is only doing the reverse charge when you want it to as to not have it connected in normal driving as it would be a smaller gauge wire. Wish that blue sea 7622 wasn't so expensive haha.

$179 from Powerwerx.com

 

[afbond03]

If anyone is looking to buy the Blue Sea 7622 and you've not used Jet.com before head over: https://jet.com/product/BLUE-SEA-76...AY-W-MAN-CTR/d96f21e8841041a58dcd93a9b7e594b8 and coupon code 20NOW should bring the price down to around $155

 

[Herbie]

I have a dual battery TMAX system but it doesn't work anymore, I think the relay is dead.
Which kind of relay can I use to replace it ? I think it's 250 ampères...

I've been out of this thread for a while, but hopefully you haven't spent more than needed on this. You do NOT need a voltage sensing relay if you already have the T-Max battery system, the voltage sensing, delay, etc. is all handled by their control box. You're likely correct that your solenoid is dead - my T-Max one went after about 18 months, and didn't seem to be very high-quality. I replaced it with a 200A Cole Hersee unit (link), $34. This has been rock solid for 4+ years now.

Also: I keep seeing the 250A number associated with the T-Max system, but I sort of doubt that original solenoid was really capable of that current, which might be why they seem to fail. The physical size of the can and its relative "light" weight compared to the 200A Cole Hersee version doesn't inspire confidence.
2nd Edit: I bought the version of the T-Max kit that included power cables, and they were only #6 gauge, so definitely not anywhere near 250A. I chopped up some #2 jumper cables instead.

 

[mrthrun]

Great post, my Roadtrek, with this system is being parked for the winter. I want to run a trickle charger but don't know how to hook it up. If I connect it to the main battery will it charge the whole system, or do I need two trickle chargers or is there another way?

Thanks.

 

[DiploStrat]

...
A voltage sensing combiner relay, draws current operate in the 'combined' position.
Trickle charger would need capacity (what it may or not be able to provide)
to operate this relay as well as furnish charging to the batteries.

Most do, some don't. I believe that the Blue Sea ACR uses their magnetic latching technique, in which case, it only requires current when changing state, not when holding it. In any case, you are best served by a charger which is:

A) Big enough to handle any current required to hold the relay closed, and,

B) Smart enough to drop to a true float when the batteries are charged.

 

[AndrewP]

Most do, some don't. I believe that the Blue Sea ACR uses their magnetic latching technique, in which case, it only requires current when changing state, not when holding it. In any case, you are best served by a charger which is:

A) Big enough to handle any current required to hold the relay closed, and,

B) Smart enough to drop to a true float when the batteries are charged.

It will still need some current to run the control electronics though that's pretty small-The spec is less than 40mA, but likely less than that. I think when latched, it draws about 130mA to keep it latched, but most of the force keeping the relay closed is from the permanent magnets inside the unit. If you remove all power, does the relay open? Bet it does. If not, that would potentially be somewhat dangerous.

Interestingly the smaller ACR without the magnetic latch, draws most power to keep it closed-175mA. That's still pretty efficient as things go.

Totally agree about A and B.

Just for the record, I float 5 FLA batteries in 3 trucks with 2 ACRs with about 0.4 amps (400mA). The ACRs themselves account for .35 amps (350mA).

 

[mrthrun]

Keeping things simple.
Were I laying up for winter, But without an automatic voltage sensing combiner/isolator relay.
I would simply place a light weight jumperclip across the 'batt terminals on the relay,
Then connect the tricklecharger to whatever battery is most handy.

A voltage sensing combiner relay, draws current operate in the 'combined' position.
Trickle charger would need capacity (what it may or not be able to provide)
to operate this relay as well as furnish charging to the batteries.

Just remember to remove the jumper during its springtime firing up process.

Thanks, I really over think things. When you say light what gauge of wire would you suggest? Also, I have a 20 watt solar panel with a voltage regulator, would that be okay or should I use my cheap Walmart trickle charger?

 

[evldave]

Thanks, I really over think things. When you say light what gauge of wire would you suggest? Also, I have a 20 watt solar panel with a voltage regulator, would that be okay or should I use my cheap Walmart trickle charger?

I use a 20 gauge jumper wire for this. Bought it at radio shack (I put a link to them somewhere earlier in the thread). You aren't using it to run a lot of current, so just about any wire would work (typically Cat 6 wire is rated at a higher current load than the most solenoids need to trigger, although I wouldn't use it for long-term maintenance :sombrero.

 

[mrthrun]

Sounds good, thanks. I don't know why but Radio Shack is now called the source here in Canada; I liked the name Radio Shack better.

 

[evldave]

You might take a tip from the Elevator Industry, Make that jumper of a ungodly bright obnoxious color, somewhat long & leave it draped across other stuff so its absolutely visible anytime its compartment is opened.

This is important - I have had to jump start the battery a couple times using my mini-jumper (OBDII reader doesn't shut off automagically). If you forget and leave it connected while the car is running, this can cause some oddity in modern cars. For my H3, it creates some kind of feedback loop that makes it so the truck won't shut off. Yep, no logical reason why, but if I leave the jumper connected and drive the truck, it won't shut off when I turn the key and take it away - will run forever until I either run out of gas or disconnect the jumper.

Moral of the story: Make sure you disconnect the jumper before you drive away

 

[mrthrun]

Thanks Verkstad, I did what you said with a little mod. I couldn't reach the isolater well but was able to figure out which side was main and which side was auxiliary, hooked up the (+) side of the charger to the auxiliary side of the isolater and ran a jumper from there back to the main battery. Hooked up the negative side of the charger to the main battery. Tested both sides of the isolater with a voltmeter today and both batteries are fully charged.

Thank you so much for your post. I hooked up the solar panel to my truck that is parked for the winter. The sun has finally come out today after a week of cloudy weather and the battery is charging and at about 12.6 volts. Will monitor that for a week.