Sizing Transformer For Solenoids

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fifty60

fifty60

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I have several 115V solenoids that I need to supply from a 460V source. I will use a general purpose transformer to step down the voltage to the solenoids. The solenoids have a 180A inrush, with a 35A holding current. Do I need to size the full 180VA into the size of the transformer?

I also have other loads on the 115V secondary. A small 90W crankcase heater, a small exhaust blower that draws around 2A fla, and timers, relays, and other control related components.

I know a lot depends on the frequency of operation of the solenoids. The solenoids should not be operated more than a few times an hour. Would I need to use the 180VA, or should I use the 35A holding current and multiply that by some factor?
 
EMALS

EMALS

I had to do this for a prototype design for an Electromagnetic Aircraft Launch System, intended to replace the steam/boiler launch systems. Each breaker had to tolerate the inrush for its duration, which meant going to the breakers Time Current Characteristic curve for verification.
For transformer sizing you'll need to see how many could come on together and sum those up, then plot the transformer's ANSI damage curve and verify it doesn't exceed the transformers primary and secondary protection.
 
if you are using a GP xfmr, you probably need to allow for the inrush.

machine tool transformers will allow for the inrush though. a rule of thumb for machine tool transformers is to size it no smaller than the total load plus 1/3 - 1/5 the maximum inrush.
 
Hydraulic guy here, uses systems with lots of solenoids, most larger than yours ... I agree with Mr. Peterson; in your case ("several"*35)+(90)+( 2*115)+(0.3*180*max number being energized in a an approximate 0.2 second period). Parentheses were used for clarity.
 
petersonra said:
if you are using a GP xfmr, you probably need to allow for the inrush.

machine tool transformers will allow for the inrush though. a rule of thumb for machine tool transformers is to size it no smaller than the total load plus 1/3 - 1/5 the maximum inrush.
Click to expand...
Yes, machine tool transformers are designed for such loads as the secondary winding ratio is compensated to allow for this type of load unlike the common GP transformer. If I can recall I believe that the manufacturers may have some sales references for MT transformers included in their catalogs.
 
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