Generator Start Amps Test
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From: Wyoming
Generator Start Amps Test
Today I tested the maximum startup amp load by my on-board Onan 5500w generator. More on why I need to know that number below.
According to my Fluke 325 meter, the generator used 77 amps during the startup process (not including priming the fuel system). That's around 30% of what I was expecting. The starter cranked for a good 15 seconds before it fired. The temperature during the test was in the 30's. I'm wondering if I set up the meter right. The clamp was around the negative lead, coming directly off the battery. The flooded lead acid battery is on the tongue and is isolated from the rest of the trailer. The only items on that circuit are the generator, tongue jack, trailer break away brake system and an air compressor. The generator is located by the tongue. The wires from the battery on the tongue to the generator are no longer than 6'.
I installed a 560 Ah LiFePO4 battery bank this fall in my 22' bumper pull toy hauler. 560 Ah sounds like a lot and it is. But I designed the system for longevity over a period of days, instead of high, short term, output. The BMS used by the two batteries that I built each have a maximum discharge rate of 120 amps, for a total of 240 amps across both batteries. I wasn't sure if my new LiFePO4 battery bank could handle the generator's high amp load at startup. LiFePO4 batteries aren't often used as starter batteries. There isn't much information out there for this. The Onan service manual doesn't provide any guidance, other than requiring a battery with 440 CCA.
I've seen a couple tests, on smaller Onan generators, that returned a maximum startup load of over 200 amps. Those results are causing me to doubt the results of my test. I would be quite happy to find that my generator needs only 77 amps to start.
According to my Fluke 325 meter, the generator used 77 amps during the startup process (not including priming the fuel system). That's around 30% of what I was expecting. The starter cranked for a good 15 seconds before it fired. The temperature during the test was in the 30's. I'm wondering if I set up the meter right. The clamp was around the negative lead, coming directly off the battery. The flooded lead acid battery is on the tongue and is isolated from the rest of the trailer. The only items on that circuit are the generator, tongue jack, trailer break away brake system and an air compressor. The generator is located by the tongue. The wires from the battery on the tongue to the generator are no longer than 6'.
I installed a 560 Ah LiFePO4 battery bank this fall in my 22' bumper pull toy hauler. 560 Ah sounds like a lot and it is. But I designed the system for longevity over a period of days, instead of high, short term, output. The BMS used by the two batteries that I built each have a maximum discharge rate of 120 amps, for a total of 240 amps across both batteries. I wasn't sure if my new LiFePO4 battery bank could handle the generator's high amp load at startup. LiFePO4 batteries aren't often used as starter batteries. There isn't much information out there for this. The Onan service manual doesn't provide any guidance, other than requiring a battery with 440 CCA.
I've seen a couple tests, on smaller Onan generators, that returned a maximum startup load of over 200 amps. Those results are causing me to doubt the results of my test. I would be quite happy to find that my generator needs only 77 amps to start.
