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Forum Index : Electronics : Allegro Amp calculation
| Author | Message | ||||
| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi, My bi-directional Allegro hall sensor reports 0 Amps at Vcc/2 or 2.5V. It would report 50 Amps at Vcc or 5 Volts. Now 2.5 V corresponds to 50 Amps, so we get 2.5V/50 Amps = 50 mV/Amp. Surely Allegro is correct in their data sheet when they claim 40 mV per Amp and I am wrong with my 50 mV/Amp. Where is my logic incorrect?? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
If you check the specs for the 50A uni directional unit you'll see 60mV/A. So I guess your calculated 50mV/A falls right between these two 50A versions  .
I bought some of these units recently and I'll stick with the 40mV/A specs Allegro supplies. Just have to finish the little PCB's and I'll be able to test what the output is exactly. Klaus |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks Tinker. Best to stick to the Allegro specs. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Hi domwild I just tested my Allegro current sensors. I have the ACS 758 types in 050B and in 100B range. At 30A current (checked with a DC clamp meter) I got 38mV/A on the 050B. On the 100B the 30A test current gave 16mV/A. The latter is a fair bit below the printed 20mV/a specs, will need to do some further testing - have to make a bigger water cooled load first. I did use a 33uF capacitor at the Vout terminal, with this size cap it takes a while before the output stabilises. Klaus |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Tinker Check you clamp meter against another meter. I've been caught out before with meters that I trusted, but found they were reading wrong. Also did you have a bypass cap, say .01 - 0.47uF, across the +5 and ground pins. The output can be noisey without it. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Yes Glen, I did use a 103 bypass cap. I read your blog on these things too, found cutting the current connecting tags from 1.6mm copper sheet is a lot easier than flattening copper tubing for that purpose 
Not sure about the clamp meter - it was not a cheap one and it has a zeroing button. I suppose I could check it against a conventional 100A shunt. Klaus |
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