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 > Generator start leads

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time2roll

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Posted: 10/15/21 04:30pm Link  |  Quote  |  Print  |  Notify Moderator

First make sure that LFP battery is rated for 500 amps. I would use a 350 amp Class-T from the battery to the bus. Connect the generator direct to the bus. The fuse should pass 500 amps for at least a minute, while a direct short should open the fuse before the wire melts.


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memilanuk

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Posted: 10/15/21 04:35pm Link  |  Quote  |  Print  |  Notify Moderator

The LFP batteries I'm building have a JBD 150A BMS that is rated at 160A for 10 seconds, or 890A instantaneous (each). Both of them in parallel shouldn't have a problem starting the generator. One by itself... it'll be interesting to see.

HMS Beagle

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Posted: 10/15/21 06:36pm Link  |  Quote  |  Print  |  Notify Moderator

memilanuk wrote:

Well, until someone else actually puts a meter on the start leads a similar Onan 2500 LP generator...


Got everything back together, started the generator with the meter clamped on one of the start leads. Let it run about 15-20 minutes, then shut it down. Pulled it out, took the first pick, cleared the MAX hold, set it again, and about 15 minutes later, started it again.


I'm still quite skeptical of the measurement. Even as a transient. I've measured a few small engine starters with equipment designed to record the transients and never seen anything that high. That meter was not designed to measure rapidly varying currents, and a starter motor, even when cranking at steady state has rapidly varying currents.

Here is an example of the voltage and current starting my 1250cc BMW motorcycle (100 HP 4 cylinder). Current varies between about 160 and 60 amps with each compression stroke. Either your meter is wrong or your genset starter is seriously damaged.

[image]


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jimh425

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Posted: 10/15/21 06:56pm Link  |  Quote  |  Print  |  Notify Moderator

My guess is a 1250cc BMW requires a lot more power to run the starter because the compression is likely a lot higher.

I’ve jump started my Onan 2500 LP with 14 gauge wire that was 15 ft long. That was clipped to my TC battery with alligator clips and to my truck battery. So, I don’t think the Onan’s take that much to start.

No idea how much that is, but I don’t think very much or wouldn’t the wire burn up?


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memilanuk

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Posted: 10/15/21 10:59pm Link  |  Quote  |  Print  |  Notify Moderator

Depends on how long the duration is. Think of it like a slow-blow fuse [emoticon]

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Posted: 10/16/21 10:45am Link  |  Quote  |  Print  |  Notify Moderator

So 3 pages later, I’m not understanding the issue other than OP thinks his starter may draw too much for the fancy new system being installed?
Why not just hook it up and go. 2 big lfp batteries even half dead will start a little generator. One lfp that is about the size of a spice tin with 135cca and 4ah reserve will start my 450 bike with like 12.5:1 compression.
Idk why it shows 300-400A. But unless there’s cause to think something is wrong with the starter, this seems like a non issue in search of problems


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memilanuk

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Posted: 10/16/21 08:02pm Link  |  Quote  |  Print  |  Notify Moderator

The original question - in my mind, as the OP - was for people who actually have (or have had) onboard generators, about how they found them wired from the factory/dealer. Were they fused, or not? The discussion was never intended to be about what the starting current is or isn't.

As I build out the new system, there seems to be strong recommendations to use appropriately sized fuses to protect various segments - but as found, the cables are landed directly on the battery terminals, completely inside any form of overcurrent protection.

Looking at the OEM install manual for the Onan 2500 LP generator(s)... it recommends #2 AWG for installs up to 45 ft (total round trip length). It recommends *against* using the frame for the negative return if possible, and while it calls out specific torque values for the connections, it doesn't show or recommend anything specific as far as OCPD. Also, it mentions having a battery with a minimum of 360 CCA, on up to 1000 CCA.

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Posted: 10/16/21 08:53pm Link  |  Quote  |  Print  |  Notify Moderator

memilanuk wrote:

The original question - in my mind, as the OP - was for people who actually have (or have had) onboard generators, about how they found them wired from the factory/dealer. Were they fused, or not?


Everything is fused as 12V or 110V as far as I can tell. I have a fuse box with easily accessible fuses or breakers in the case of 110V..

memilanuk

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Posted: 10/16/21 10:24pm Link  |  Quote  |  Print  |  Notify Moderator

jimh425 wrote:


Everything is fused as 12V or 110V as far as I can tell. I have a fuse box with easily accessible fuses or breakers in the case of 110V..


I'm betting your generator start leads ain't coming from the house AC/DC distribution panel...

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Posted: 10/16/21 10:39pm Link  |  Quote  |  Print  |  Notify Moderator

I’ll try to look soon, but I’m pretty sure there is a 12V fuse for the generator.

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