PSC55-12 component info?

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PSC55-12 component info?

Postby bryant on Tue Aug 18, 2015 1:20 pm

Thanks for adding me to the forums.

I have a pair of PSC55-12 chargers (337A/338A) that are inoperative; I don't know their history, other than that they were allegedly installed on a boat. A visual inspection shows that the component at position RT1 on the circuit board is ruptured, with a lead parted, on each of them. My guess is that this component is an NTC thermistor being used to limit inrush current, and that these units may have experienced a power surge that destroyed the component, but obviously I'm just guessing. All other components, including the big transient-absorbing caps, appear to be intact and in good condition. Of course, that's just visually so far.

I know that you do not publish schematics, and that's understandable. However, I wonder if you would be willing to provide the specifications for the RT1 component so that I might obtain some replacement parts; it appears to be a straightforward job for me to replace it. I would very much appreciate any information you can offer. If I could purchase the components from APC, that would be excellent.

I've been working with Ample Power gear for about a year. I appreciate the focus on precision and efficiency reflected in it and the docs. I've learned a ton from the "Living" and "Wiring" books.

Thanks in advance!

-- Chris
bryant
 
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Re: PSC55-12 component info?

Postby Coulomb on Thu Aug 20, 2015 12:20 am

I don't have the part number specs for that device, but it's failure was probably caused by a high voltage transient. That would probably destroy other components,

You can test for that using a 10 ohm resistor in place of RT1. You just won't be able to supply much load current with the resistor.
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Re: PSC55-12 component info?

Postby bryant on Fri Aug 21, 2015 4:28 pm

Thanks for the response and advice David. After installing the 10-ohm resistor, voltage is present at the outputs. The readings are slightly off the spec given in the SCM Troubleshooting guide -- 13.55 V (control plug out), and 14.15 V with the DV leads shorted (control plug in) -- but then again, there's some non-spec resistance in the circuit. It's pretty amazing in any case; the PSC appears to have taken a licking and kept on ticking. Perhaps RT1 served the sacrificial role and saved the big caps and the rest of the crew.

Since you suggested a 10-ohm resistor for the test, I assume that 10 ohms is a good value for the initial resistance of the inrush NTC thermistor. From the power rating of the PSC55, it looks like it will need to handle something in the neighborhood of 8 A steady state current when the PSC is running full tilt. I will try replacing the 10-ohm resistor with an NTC part with these characteristics, like an Ametherm SL22 10008, and see how it goes.

Thanks again for your help!

-- Chris
bryant
 
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Joined: Mon Aug 17, 2015 3:26 pm

Re: PSC55-12 component info?

Postby Coulomb on Mon Aug 24, 2015 2:01 pm

That looks like a good choice. There just needs to be some inrush limit to prevent nuisance circuit breaker action.
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