Transcend 247BH Lead/Acid -> LiFePO4 conversion

[AndrewSmith]

Hello

After a lot of planning I finally got it done. Here are the wiring diagrams, which I had to make myself. Thanks to everyone on this forum who provided suggestions, especially Country Campers who posted about his experience and was an inspiration, and Jlawles2 for helping me figure out the fridge wire.

I will post some photos once I make them. I did a lot of the work at night (to get it done before a trip) so I didn't have much time for documenting it, except the diagrams which were crucial for the success of the project. Every minute I spent drawing out the circuit and updating it saved me hours. The work itself took less than two days (including a quick order from Amazon and a visit to Princess Auto).

BEFORE:



AFTER:



Yeah, I guess one needs some experience with electrical circuits before attempting this

[Country Campers]

AndrewSmith

The one thing that I see is you may want to move the load wires on the batteries to opposite ends, positive on the left battery , negative on the right battery, for load balancing, others may correct me on this. From what I have learned it is best to not have the load connected to the same battery , unless you only have one battery.

Congrats on the setup and glad I was "inspirational", if I can do it anyone can.

Brian

[AndrewSmith]

When I was experimenting I had the charger connected to the same battery on one end, and measured the voltage drop to the second and third battery. With 4gauge wire it was about 0.1V for each hop if I remember right. So I guessed that it would be best to have at most one hop from the load to each battery. But perhaps that wasn't the best decision?

[Country Campers]

It is my understanding that , from your diagram, the center battery will do most of the "work" while the outer ones fill in when needed. If you wire it as positive to the left battery and negative to the right battery all 3 batteries will be sharing the work load, if I am understanding and remembering the concept correctly.

Brian

[AlexPeterson]

When I was experimenting I had the charger connected to the same battery on one end, and measured the voltage drop to the second and third battery. With 4gauge wire it was about 0.1V for each hop if I remember right. So I guessed that it would be best to have at most one hop from the load to each battery. But perhaps that wasn't the best decision?

AndrewSmith How many amps was your charger supplying at the time you measured it? What is the resolution of your voltmeter?

If you are using AWG #4 copper wire, the resistance per foot is .00025 ohms/ft. Assuming 100 amps per battery, their max, and further assuming the wire connecting the outer batteries to the middle one is one foot long, you'd see 100a x .00025 ohms = .025 volts per line. Double this to account for total voltage drop the "outer" batteries see and you are at .05v (positive and negative cables). This would be assuming 300 total amps. For this discussion, I'm ignoring that 300 amps is way too much for #4 wire...

This is the balanced arrangement that Country Campers is suggesting would be better. While better, it does not completely balance the system, as now the middle battery is the odd man out and sees a different voltage than the outers.



The only truly balanced arrangement is something like this:



How much difference these imbalances make I do not know, it totally depends on how many amps you plan to charge them with or draw from them.

AWG wire reference https://www.powerstream.com/Wire_Size.htm

[Country Campers]

AndrewSmith


As you can see from AlexPeterson post above the balancing does not accomplish much just wanted to throw it out there.

Brian

[howson]

AndrewSmith , Country Campers and AlexPeterson ;

I went through the same process and discussion with Garret Towne (AMSolar engineer). I posted a synopsis here: https://gdrvowners.com/forum/solar/7...4879#post74879

Howard

[AndrewSmith]

Thanks for the suggestion everyone, I moved the load leads to the opposite batteries. The counting links trick mentioned here was really handy.

[AndrewSmith]

Here are some photos of my setup:

BATTERY BOX

The packing foam from the boxes the batteris shipped in was very handy. I won't need to worry about them rattling to death in the trailer. It turns out to be very easy to cut on a bandsaw, I never thought of doing that before.


The box is screwed into two sides of the storage compartment under the bed. It will not move:



BATTERY BANK





BATTERY MONITOR

This didn't work as well as I hoped. The LCD on the poorly-made battery monitor is not readable from this angle. So I have to get down on my knees to read it. But at least I didn't need to break into the kitchen wall and cabinets:



I could have done something nicer with this wire. And one day I'll have to protect the connector from stuff that will get thrown into the storage compartment. For now it's good enough:

[AndrewSmith]

REWIRING

This box was in the trailer originally, on the front left. I only added a thicker piece of plywood on the back to screw in the circuit breakers. The "disconnect" was only used for the converter. Now it's much better organized. And protected from corrosion. Check out how lucky I was making that hole for the battery leads







I am officially proud of myself Sometimes being anally organized pays off

[AndrewSmith]

And this is why such connections should never be exposed to the road:





Of all those only two wires (plus the black hair) are left. I crimped on some good quality tinned enclosed connectors, filled with grease, taped, and heatshrinked. Still, I expect to have to remake that connection one of these years.

It only takes one covering of road-salty-snow for the connections to start corroding. After less than 3 months the copper disintegrates into purple dust.

Grand Design should have known better. I imagine Indiana isn't that much warmer than southern Ontario.

[howson]

AndrewSmith -- may I make one more suggestion? Cover the positive battery terminals with something non-conductive so there's not an inadvertent shorting of a battery. (That would be really bad.)

Something like the cover shown below (one on each + connection):



Howard

[Country Campers]

AndrewSmith

The pics in post #10 did not load.

Good job done with this project, congrats.

Brian

[AndrewSmith]

AndrewSmith

The pics in post #10 did not load.

Good job done with this project, congrats.

Brian

Thanks Brian! I edited the post and reuploaded the photos, hopefully they show now.

[AndrewSmith]

AndrewSmith -- may I make one more suggestion? Cover the positive battery terminals with something non-conductive so there's not an inadvertent shorting of a battery. (That would be really bad.)

One day I'll cover all the batteries with a piece of plywood, like a roof. That will keep pillows and such out of the batteries too.

For now I'm out of juice, and I just ripped the staircase out of my house going to the second floor, that gave me a serious project deadline