Electronics > Projects, Designs, and Technical Stuff
Measuring A Car battery
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challie2:
Hi all

I hope I find you all at a good time.

I need some help for a project that monitors a battery amperage.

The idea is too create a display stand that measures the current draw from a car battery through a device I have made, and I want to demonstrate the performance. I plan too use one of those Chinese Digital Ampmeters found on Ebay with a 200Amp shunt, there is not going too be any load or consumer on this circuit i.e a starter motor, so would I require a power resistor to ensure the battery wont go bang? I get the idea of the shunt which is a low resistance path and the Ameter is connected across it in parallel. However would I need a power resistor to put a load on the battery circuit if so what size would I need? 12V Battery 200Amp Draw.

This is the Ampmeter I intend on using
https://www.ebay.co.uk/itm/DC-200A-Digital-LCD-Ammeter-amp-Meter-Monitor-battery-Charge-Discharge-DC-12V/332659117757?hash=item4d74074ebd:g:wikAAOSwX3FbAq9Z

Thanks

Jamie
InductorbackEMF:
Hi,you say there is not gonna be any load on the battery, (open circuit) if so how would you measure the current draw?

Also yes you would need a power resistor at 12v you need a .06 ohm resistor to limit the current to 200A a VERY big one indeed at 2.4kw!

Alex.





InductorbackEMF:

--- Quote from: InductorbackEMF on May 01, 2019, 05:37:49 pm ---Hi,you say there is not gonna be any load on the battery, (open circuit) if so how would you measure the current draw?

Also yes you would need a power resistor at 12v you need a .06 ohm resistor to limit the current to 200A a VERY big one indeed at 2.4kw!

Alex.

--- End quote ---

To get the size of the resistor you need use this

Divide the voltage by the current you want to get the resistance.

And times the voltage being drop`ed by the current to get the power.

NiHaoMike:
Just get a big inverter and a hair dryer. Might not be the cheapest option but it can easily be repurposed.
IDEngineer:

--- Quote from: NiHaoMike on May 01, 2019, 05:48:31 pm ---Just get a big inverter and a hair dryer.
--- End quote ---
Good idea if he needs to pull a lot of amps for his demonstration. An even cheaper and easier approach, if he wants to pull single digit amps, would be a car headlight. Literally designed for 12VDC application, readily available, cheap, nonpolarized, graceful failure mode, and almost zero safety issues.

So there you go, OP: Two good ideas, depending upon how many amps you want to draw.
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