Diy hi voltage cutoff circuit exist?

[rmay635703]

The old TV guy down the street has a calibrated over voltage cutoff "relay" for an old 6v battery, effectively when the voltage exceeded 7v it clicks off and stays that way, much like a circuit breaker. It was overcharge protection in the 1930s

I am curious if such a thing exists for other voltage batteries or perhaps could a hi voltage cutoff be made for say a 48v pack?

This would be a much cheaper solution than a charge controller and much more usefull for those of US who are going to be watching and interacting with our system anyway, in my case an electric car. I would turn on the system in the morning drive to work and if overcharge occurs the line from the panels would click off. (not likely but possible)

Any ideas how this would be accomplished with modern components?

[Mike90250]

1) a simple relay cut-off will not allow full charge to a battery bank. You will kill your batteries early with soemthing like that,

2) while you are driveing, you will NEVER overcharge batteries with panels able to fit on top. it might take a week of parked in the sun, before the panels will top off the batteries.
You might get 800W of solar on top, which is only about 15A, if the sun angle is perfect. For a 48V EV, you are likey using 90A rolling down the road, so your daily consumption will be way higher than your PV charge capacity. Morningstar has the most likely charge controller for you , Tristatar MPPT 45A @ 45V = about 2500W of solar

[rmay635703]

1) a simple relay cut-off will not allow full charge to a battery bank. You will kill your batteries early with soemthing like that,

No I will not, simple reason is that I will be CHARGING the car at night every night, the purpose of the solar array is to prevent sulphation while the car sits partly charged in the parking lot. One possibility however to expand on the relay method would be to add a resistor in parallel that limits current to a rate that cannot overcharge my batteries. Or if there is a method to turn the relay on if below voltage X and turn off when above voltage Y until X is reached. My main concern is that my father will be using one of the cars and he really likes to make situations where stuff is destroyed. If there is a way, he will find it. If he left the car sitting unused for a while I don't want a possibility of destroying the pack.

2) while you are driveing, you will NEVER overcharge batteries with panels able to fit on top. it might take a week of parked in the sun, before the panels will top off the batteries.

Yes I know this; which Is why I don't believe I need a real charge controller

You might get 800W of solar on top, which is only about 15A, if the sun angle is perfect. For a 48V EV, you are likey using 90A rolling down the road, so your daily consumption will be way higher than your PV charge capacity. Morningstar has the most likely charge controller for you , Tristatar MPPT 45A @ 45V = about 2500W of solar

Hmm, sounds very expensive.
But...
800 watt, amazing, at first I only wanted 10 watt on top to run the desulphator but then I started thinking that more would actually keep my batteries living much longer and may be inexpensive enough that I won't go bankrupt. Thing is I can solder and have repaired circuit boards so I figure I could build an experimental set or repair one if I could locate used ones in wisconsin.

Also that EV only uses about 75 amps once up to top speed but much more getting there.

Thank You
Ryan