I’m looking into a project that will monitor voltage across 3 12V deep cycle batteries connected in series. If the voltage drops too low, the sketch will cut the power across the batteries. The load on the batteries could be pulling up to 100 amps.
I was looking into using a relay for this, but finding one that can handle 100 amps @ 36VDC is not easy and appears to be not cheap.
So two questions;
- Can you recommend a place to find such a relay?
- Is there a different way to solve the problem? Maybe I’m not thinking about it the right way.
I would recommend you to use a simple 12V relay for a car starter. This would triggered with a smaller Arduino relay kit.
The big relay could be something like this Amazon 100/120/200A Relay which could be triggered with a 12V power source trough a smaller relay like THIS If you have any further question, im happy to answer them!
Maybe something like this?
I use a 30 amp version of this and can switch it on/off with an Arduino Due.
Here's a high current relay:
These should never ever be opened under load like that.
If you are in the yard when these are opened under load you fill your pants.
What is your load that draws up to 100A?
Car starter solenoids are not rated for continuous operation, they will overheat rapidly.
You either go with an expensive DC contactor rated for the current, or MOSFETs/SSR
Is your load inductive?
A latching type relay should work ... they rate the DC switching capability by power. This one can switch 5,600W (200A @ 28VDC). Therefore, you should be able to reliably switch 100A at up to 56VDC. Would need to pay close attention to the driving circuit as they operate on impulse and have dual or single coils.
200A Latching Relay
If its rated for 28Vdc at 200A you cannot infer its good for 56Vdc at 100A - the relationship
is not linear, it depends on spark (plasma) dynamics.
However 36V is closer to 28V so its not too infeasible it will work - you could try asking the manufacturers.
Mechanically switching high power DC is really difficult, there are no zero-crossings to break the arc and
lots of power available to keep the arc going (several kW in fact). If you get it wrong the relay will be
destroyed pretty fast (ie don't assume a 200A relay can tolerate 300A occasionally, be much more
conservative if you want trouble-free operation).
They have an incredible amount of switching force (24W coil power, 200ms impulse), 9.6mm contact creepage, max switching voltage of 440VAC.
I agree with Mark to check with the manufacturer with your requirement.