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Fuses again

PostPost by: Robbie693 » Fri Jul 02, 2010 6:46 pm

Ok - I got the message :lol:

Thanks everyone

Robbie
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PostPost by: Galwaylotus » Fri Jul 02, 2010 7:14 pm

Be careful as many meters are limited in the amount of current they can pass. It's often a maximum 10 amps and mine is fused so anything over that means a fuse replacement. Problem is the fuse is an odd-ball sixe and type and not easy to get. For most loads it's ok but if you're trying to measure 17A it might cause problems. Some (expensive) meters can meaure inductive dc current using a clamp on current transducer (CT). A nice toy to have but I've never wanted to spend that much on something I'd only use rarely. :wink:
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PostPost by: billwill » Fri Jul 02, 2010 8:45 pm

By George he's got it.

:lol: :lol: :lol: :lol:


Because my best meter only goes up to 10 amps, I tend to use an old ammeter from a car to measure car currents, Not very accurate but good enough for that job.
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PostPost by: Robbie693 » Fri Jul 02, 2010 10:13 pm

Galwaylotus wrote:Be careful as many meters are limited in the amount of current they can pass. It's often a maximum 10 amps and mine is fused so anything over that means a fuse replacement. Problem is the fuse is an odd-ball sixe and type and not easy to get. For most loads it's ok but if you're trying to measure 17A it might cause problems. Some (expensive) meters can meaure inductive dc current using a clamp on current transducer (CT). A nice toy to have but I've never wanted to spend that much on something I'd only use rarely. :wink:


Good tip - thanks for that, I'd probably have ploughed ahead without thought.

Better get the manual out for the meter

Cheers

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PostPost by: neilsjuke » Sat Jul 03, 2010 7:21 am

20 amps dc should be ok for what you want to do but not for setting the charging output 40 A or the starting current 500amps
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But at the end of the day stick some 35 amp in for now.
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PostPost by: bob_rich » Sat Jul 03, 2010 5:13 pm

Hi

As other post suggest it pays to be careful with meter shunts especially in low cost meter. If you think the circuit might have a lot of amps that may go over the rating I use a simple home made shunt. It is based on copper wire so it is only moderate accuracy and use the meter on a low mV range.

The shunt is designed to be a nominal 1/1000th of an ohm so 50A gives 50mV. The one in the picture uses 4 square mm copper wire and the meter is connected across 0.23Metre length.

accuracy is good enough for a lot of tasks but if something goes awry it will not blow the meter up!

on each end I put a 1/4" fast on so i can plug it in to blade fuse holders. Any connections could be use on the end to suit the task in hand. To be really safe an in line fuse could be built in if required

I have used this idea on a number of higher currents including measuring starter motor current but for that the shunt was a short length of 15mm diameter central heating pipe

hope this helps

Bob
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