CAT SR4B PMG Voltage?

[SJC1985]

Hello all,

I've got a CAT SR4B-HV generator to install and cant find the PMG voltage anywhere. Pretty sure I need this to select the proper DECS (automatic voltage regulator) model. There are three models with three nominal inputs (60V, 120V 240V).
The existing generator was an SR4 using the 240V input rated DECS. My guess is this will work for my new generator but looking at the exciters they do differ for volts/amps. Old exciter was 100V/4.4A and new one is 41V/9A. Not sure this has any bearing on the PMG voltage?

Any insight would be appreciated, Cheers!

 

[waross]

You should be able to run the set at rated speed and measure the output voltage of the PMG. The Permanent Magnet part of PMG allows the PMG to generate whenever it is turning.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[catserveng]

There are two versions of that generator, the older version used the traditional Kato style excitation system and was a nominal 125VDC 12 Amp excitation system. The newer style used the CAT style excitation system and it is a nominal 63VDC 12 Amp excitation system.

Easiest way to tell them apart is to look at the rotating rectifier assembly, if it has 6 individual diodes and the "puck" style surge suppressor, that is the older Kato style. The CAT style uses three rectangular modules, a positive diode assembly, a negative diode assembly and a surge suppressor.

The PMG's also had different ratings, but the Kato style on some frames had dual voltage PMG's that could be connected in series for 240VAC or parallel for 120VAC, that version had 4 PMG output wires, the single voltage version had two PMG output wires and was nominally rated at 220VAC.

The CAT style PMG has three PMG output wires and is nominally rated at 100VAC

If your "new" generator has a rated 41VDC full load field input then you likely have a CAT style excitation system, the PMG output should nominally be 100VAC at 120 Hz, they actual output is usually between 90 and 120VAC.

Hope that helps, MikeL

 

[SJC1985]

Bill, thanks for your input, we have discussed running it up to find the PMG voltage but this wont be possible until the engine is up and running (which may take some time).

MikeL, this all sounds pretty groovy. The old generator had the 4 wire PMG with it connected in series. The new one is the three wire and has the rectangular modules. So looks like our AVR will need to be swapped to the 120V rated one.

Thanks for the quick responses, Steve