I'm looking to create a battery tester (Ah counter + internal resistor checker).
Specs: Two different cells will be used - 100Ah, 3V cells & 200Ah, 3V cells
Ah counter discharge rate: 0.75C, so 75A & 150A respectively
Internal resistance: check to be completed at 400A (held for 10 seconds). Voltage measured before and after.
I've never done any high power design/wiring before. My experience is all in microprocessors and such. So I'd like some advice/someone to double check my design. Please and thank you.
For the Ah counter, I'm using resistor banks to draw power from the battery. I intend to use one circuit with a resistance of 0.04ohms to draw 75A (from a 100Ah battery), another circuit in parallel that would alter the overall resistance to 0.02ohms to draw 150A (from the 200Ah battery), and a third circuit that would load the battery at 400A for the IR test. I would open/close these circuits with contactors. Circuit diagram attached.
Are there any problems with this?
Questions:
1. The smallest resistors that I can find (that are rated for this power) are 0.25ohm resistors off Digikey. This means that I would need to wire 33 of them in parallel to achieve my desired voltage. Are there any better solutions?
2. I am looking to use two 200A, 12V contactors that we have in our shop, and purchase a 500A, 12V contactor as the primary one for the entire circuit. Something like this or this (the difference is coil current: 1.1A vs 130mA - I haven't figured out how this affects me yet). Is this reasonable?
3. How do I size and find a heatsink?
4. Anything else that I should be considering?
I appreciate you reading this far, and any help that you can provide!
Julia
Specs: Two different cells will be used - 100Ah, 3V cells & 200Ah, 3V cells
Ah counter discharge rate: 0.75C, so 75A & 150A respectively
Internal resistance: check to be completed at 400A (held for 10 seconds). Voltage measured before and after.
I've never done any high power design/wiring before. My experience is all in microprocessors and such. So I'd like some advice/someone to double check my design. Please and thank you.
For the Ah counter, I'm using resistor banks to draw power from the battery. I intend to use one circuit with a resistance of 0.04ohms to draw 75A (from a 100Ah battery), another circuit in parallel that would alter the overall resistance to 0.02ohms to draw 150A (from the 200Ah battery), and a third circuit that would load the battery at 400A for the IR test. I would open/close these circuits with contactors. Circuit diagram attached.
Are there any problems with this?
Questions:
1. The smallest resistors that I can find (that are rated for this power) are 0.25ohm resistors off Digikey. This means that I would need to wire 33 of them in parallel to achieve my desired voltage. Are there any better solutions?
2. I am looking to use two 200A, 12V contactors that we have in our shop, and purchase a 500A, 12V contactor as the primary one for the entire circuit. Something like this or this (the difference is coil current: 1.1A vs 130mA - I haven't figured out how this affects me yet). Is this reasonable?
3. How do I size and find a heatsink?
4. Anything else that I should be considering?
I appreciate you reading this far, and any help that you can provide!
Julia
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