PMG Applications

It was just last night I was talking to Darren Hill in North Land, you might know he’s a Kiwi I enjoy communicating with and I learn from him. There’s a lot of places in New Zealand off the Mains, and a lot of solar installs there. Darren explains that they have about half the Solar Energy that Ozzies in Sidney have to work with, this gives the Kiwis about twice the reason to have a backup generator.

Darren said, “We AE installers here are recommending investments in PV, and installing the smallest diesel generator one can get by with”. I was quite happy to hear this, as this has been my direction for 5 or more years, the larger the Gen Set, the more likely the owner will see higher than expected  Fuel/Kwh figures. Whether we invest in Solar or not, too big of generator can be an expensive mistake for the Off Gridder.

I have one customer with a 6/1_PMG generator with a gasoline powered backup,  he’s on his fourth year of running the PMG set in Stevens Pass, Washington State. He runs 8 hours a Day, 7 days a week, and when the 6/1 is down, the family is motivated to get it running again because it is hugely more expensive to do it on gasoline. This Location does have batteries, and an inverter, but no panels, the lower West side of Stevens Pass is NOT exactly a prime place to invest in PV Panels 🙁

The PMG has proven highly reliable for them, all the problems have been related to the prime mover, no drive problems, no PMG problems.

If you are starting with a clean piece of paper, I highly recommend that you look at 48 volt inverters and battery banks. I think there are a lot of reasons to start here, and pass on 12 or 24 volt systems. You might ask, what if I do invest in 48 volts, and find the even newer systems are 72 volt? well there’s reasons we’ll likely stop at 48 volts, all the Telco’s did, and for legal reasons. I think the higher voltages would likely carry more liability, and legal requirements, and this is why we’ll likely stop at 48Volts. Telcos have been using 48 volts for 100 or more years.

If you are adopt 48 volts as I have, the PMG may be your single off grid solution for 120/240 VAC, and for charging batteries directly! I am currently charging 4325 pounds of 48 volt Battery with the PMG directly, I have the two stator windings in parallel and they feed into a full wave bridge rectifier across the battery.

Above: PMG as a 48 Volt battery Charger

When it’s time to charge the battery, you operate a simple interlocked transfer switch, bring up the RPM until you see the amperage your battery manufacturer recommends you charge the batteries at. In the example above, the 1786 watts was at 32 amps, and I think the PMG could carry this type of current continuous in lower ambient temperatures. I need to monitor the test PMG at this load for about 4 hours to prove this power level. but during this test, I could not find any wire, connector or surface on the PMG hotter than 106F. The large air cooled rectifier did run around 140F with a fan blowing on it, so this part needs some attention.

So, you say you have a built in battery charger? I wonder, how more efficient might it be if we charge directly off the PMG versus using a 120VAC generator feeding into the built in charger in your inverter? I think it wouldn’t take long to measure the fuel using both methods, and see what is more efficient, and I think it’s nice to know that you have a back up charger in the PMG just in case the other one fails.

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