Author Topic: Command maximum 3A on a coil  (Read 172 times)

Offline FluidPowerTom

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Command maximum 3A on a coil
« on: January 12, 2020, 07:39:38 PM »
Suppose I'm not sure what valve coil or maybe even voltage of coil a customer is using, and I want to give that coil the full signal.  If I send a 3,000 mA command then that coil will actually just accept whatever the maximum current it can at the system voltage, right? I = V/R.  Are there any pitfalls in doing this?
Mechanical Engineer
Hydra-Power Systems - Distributor - Pacific Northwest

Offline SJ Industries

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Re: Command maximum 3A on a coil
« Reply #1 on: January 12, 2020, 08:08:41 PM »
Isnt that essentially the same as using a straight Digital output on/off?
I have never seen a coil with less than 15 Ohms?. Is it a 12v or 24v system? I think you would be pushing to find a set up that needs 2amps.

I use DOuTs for some coils and they only ever get to .9A

Offline G30RG3

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Re: Command maximum 3A on a coil
« Reply #2 on: January 13, 2020, 09:28:27 AM »
A 35+W coil will consume about 3 Amps on a 12V setup, but if your voltage is higher OR the temperatures are low, you might get a situation where the PWM-OUT goes in overload. The DIG-OUT stays course a while longer...

Offline Searfoss

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Re: Command maximum 3A on a coil
« Reply #3 on: January 14, 2020, 08:46:15 AM »
What's more likely to cause an overload? High voltage or lower temps?

Offline G30RG3

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Re: Command maximum 3A on a coil
« Reply #4 on: January 14, 2020, 09:20:42 AM »
What's more likely to cause an overload? High voltage or lower temps?

Does it matter?  A 10% higher voltage will result in a 21% higher current, but once the coil is hot, the higher resistance will compensate this to a degree.
A 33W - 12V coil resistance is typically around 4.5 Ohm at room temperature, and this value changes about .4% per degree centigrade.
What matters here, is how the controller handles the current limit, ans as far as I know, the PWM output is overload-triggered sooner than the DIG-Out.

Offline SJ Industries

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Re: Command maximum 3A on a coil
« Reply #5 on: January 14, 2020, 08:48:33 PM »
I rarely work with 12v systems, or coils that draw that much current, thank you for posting that info I will keep a look out for it in the future.