Author Topic: What size transformer do I need?  (Read 747 times)

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Offline iXodTopic starter

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What size transformer do I need?
« on: December 05, 2019, 05:15:08 pm »
A 36vdc gear motor is PWM’d (using a MOSFET) to achieve variable speeds. The unregulated  supply is full-wave rectified and filtered with a single 1000uF electrolytic cap.

The original transformer secondary went open-circuit and a replacement is NLA.

What secondary voltage should I use to achieve the 36vdc needed to drive the motor?

Thanks.
 

Offline SeanB

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Re: What size transformer do I need?
« Reply #1 on: December 05, 2019, 05:23:37 pm »
Around 28VAC, though you probably, unless that is a really tiny motor, will want a little more capacitance on the transformer. Current rating will also have to be around 1.5 times the full load current of the motor, unless you have some operating time limits that have the motor running at low power most of the time, and rare full power operation, though I suspect your transformer was undersized for that reason, so it was cooked nicely.
 

Offline iXodTopic starter

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Re: What size transformer do I need?
« Reply #2 on: December 05, 2019, 05:52:28 pm »
Motor label says 36 vdc, 30 watts. No HP or amps rating.

So 6.25A at 28 volts should be good? ::

https://www.mouser.com/ProductDetail/Bel-Signal-Transformer/A41-175-28L?qs=sGAEpiMZZMvwUzoUXIIvyZ8riR3Pta28dcX6E4y%2F7GMRhEVEAcvW3w%3D%3D

Thanks.
« Last Edit: December 05, 2019, 06:18:49 pm by iXod »
 

Offline SeanB

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Re: What size transformer do I need?
« Reply #3 on: December 05, 2019, 08:01:13 pm »
Should work well enough, and large enough that it will survive stalled operation for a while, at least longer than a fuse takes to blow. Bit overkill, you could get by with a 3A transformer and still work, but so long as the bigger one still fits in the same volume it will work. The A41-80-28L will also work with your motor load, as it draws only 1A roughly, with probably a 3A start up current, which the transformer will survive easily with little problems.
 


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