What size shunt to use ??

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collectors
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Location: Fair Green, Norfolk
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What size shunt to use ??

#1

Post by collectors » Fri Mar 06, 2020 8:54 am

Hi, slightly off topic but hoping someone here can help. Apart from trains i also like RC electric model aircraft. Now the larger electric planes can run at quite high amperage, so i thought it would be handy to fit an ebay volt/amp meter to the plane permanently as you can test on the ground what amps are being pulled when changing a propeller. Problem is i am not sure what size shunt to use. Now the motors can quite often pull 60+ amps, so i am assuming a to go for a 100amp shunt. But they come in different Ma versions & it was this part i wasn't sure on. "What size milliamp to use" The batteries used are 5amp hour 14.5 volt lipo's.

Thanks

Tricky Dicky
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Re: What size shunt to use ??

#2

Post by Tricky Dicky » Sun Mar 08, 2020 3:27 pm

Sorry cannot help you out as it would require information about the ammeter namely it’s internal resistance. However this site shows you the calculations required.

https://circuitglobe.com/ammeter-shunt.html

Go down to related topics and under the heading shunt resistor you will see how to get full scale deflection.

You do realise the shunt resistor for the currents you are talking about would be quite sizeable as it needs to be quite low resistance compared to the meter to shunt the majority of the current away from the ammeter and at the same time dissipate any heat as heat would alter the shunts resistance.

Richard

collectors
Posts: 137
Joined: Sun Oct 21, 2018 1:48 pm
Location: Fair Green, Norfolk
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Re: What size shunt to use ??

#3

Post by collectors » Mon Mar 09, 2020 8:33 am

Thank's Richard, its pointed me in the right direction & it looks like these meters read of a shunt anywhere from 10-100amp & all are @ 75mV. Just need to get the correct size amperage to be safe. I will try one of these & compare to my amp meter. If it works, fine. If not, it was only a couple of quid.

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