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Old 12-27-2016, 11:45 AM   #1
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Portable 12v Jump Starter

Hey everyone... hope you had a pleasant holiday

I screwed up and killed my batteries by leaving the water heater / bay heater on without charging up the system using the generator. I literally just forgot on Christmas day to go charge the batteries. Ugh.

So I'm thinking this is the perfect time to get a 12 v jump pack - I've been meaning to get one anyway and this seems like the right excuse. But I'm not sure what amp output I'll need. I don't want to waste money by getting one that's bigger than I'll need, but I don't wanna buy one that's too small to work correctly, either. I searched the forums but couldn't find info specific to the required amperage output I'll need.

I'm not trying to start the main engine; I really only need it to start the generator - an Onan 7.5 QD.

Any help would be greatly appreciated. Thanks!
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Old 12-27-2016, 12:13 PM   #2
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You don't give a lot of information about your coach. It sounds as if your genset starts from the house batteries (some use the chassis batteries). Therefore, you should have a good charge on your chassis batteries, correct? ...you can start the engine, correct? If so, can you use the boost switch to start the generator. You may have to hold the boost switch for awhile or hold it awhile as the engine is running.

The idea of the boost switch is to be able to connect the good bank with the bad so if one is drained, the other can connect with it to boost it enough to start the generator (assuming that your generator starts from your house battery bank which sounds as if it does) or the other way around if the chassis batteries are dread where you can't start the engine, you can borrow enough from the house batteries to start the engine.

Therefore, theoretically, you may not need a separate portable jump starter.

I'll defer to the experts to give you more detailed advice on this.
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Old 12-27-2016, 12:17 PM   #3
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This one is highly rated.

Click image for larger version

Name:	ImageUploadedByiRV2 - RV Forum1482866269.799358.jpg
Views:	160
Size:	145.3 KB
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Old 12-27-2016, 12:23 PM   #4
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Quote:
Originally Posted by theroc View Post
You don't give a lot of information about your coach. It sounds as if your genset starts from the house batteries (some use the chassis batteries). Therefore, you should have a good charge on your chassis batteries, correct? ...you can start the engine, correct? If so, can you use the boost switch to start the generator. You may have to hold the boost switch for awhile or hold it awhile as the engine is running.

The idea of the boost switch is to be able to connect the good bank with the bad so if one is drained, the other can connect with it to boost it enough to start the generator (assuming that your generator starts from your house battery bank which sounds as if it does) or the other way around if the chassis batteries are dread, drained, or low.

Therefore, theoretically, you may not need a separate portable jump starter.

I'll defer to the experts to give you more detailed advice on this.
I can't start the engine because the chassis batteries won't even light up the dash let alone turn over the engine, and the house batteries don't have enough in them to boost with.

I'm guessing some part of the water heater / bay heater runs off the chassis batts, and some other parts of the system runs off the house batts... hence why both systems are "dead."

In either case, I just need to get the generator started... I'll worry about diagnosing why they died later.

Thanks!
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Old 12-27-2016, 12:25 PM   #5
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like the poster said run engine to charge batterys and also hold down
boost switch and then gen will start
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Old 12-27-2016, 12:25 PM   #6
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Originally Posted by pasdad1 View Post
This one is highly rated.

Attachment 147592
Yep, that's the one I have saved in my Amazon shopping cart... just looking for confirmation that 1700 peak amps is enough to crank the genny and glow the plugs at the same time before I buy it

Thanks!
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Old 12-27-2016, 12:27 PM   #7
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Originally Posted by Racklefrack View Post
I can't start the engine because the chassis batteries won't even light up the dash let alone turn over the engine, and the house batteries don't have enough in them to boost with.

I'm guessing some part of the water heater / bay heater runs off the chassis batts, and some other parts of the system runs off the house batts... hence why both systems are "dead."

In either case, I just need to get the generator started... I'll worry about diagnosing why they died later.

Thanks!
awe ok now we see yes your system is most definitely wired incorrectly
never seen that set up before.not to say it does not happen. I just have never run into such
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Old 12-27-2016, 12:28 PM   #8
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like the poster said run engine to charge batterys and also hold down
boost switch and then gen will start
If the boost had worked I wouldn't have posted here... just sayin'
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Old 12-27-2016, 12:28 PM   #9
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Costco have as good or better for like 79.95
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Old 12-27-2016, 12:30 PM   #10
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awe ok now we see yes your system is most definitely wired incorrectly
never seen that set up before.not to say it does not happen. I just have never run into such
To be clear... I have no idea if this is how it's wired or not - I'm completely guessing in the dark without the necessary expertise to back it up. But the chassis batts are too dead to light up the dash and the house batts are too low to boost it.

Wired wrong or not, the system has always worked perfectly UNTIL I forgot to keep the batteries charged by running the generator a couple hours a day... hence needing the right size jump pack to get 'er started
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Old 12-27-2016, 12:32 PM   #11
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Originally Posted by select55 View Post
Costco have as good or better for like 79.95
Costco... OF COURSE. didn't even think of them, have no idea why. Thanks!
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Old 12-27-2016, 12:34 PM   #12
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Depending on the size of your battery banks, it's potential that little starter pak does little, as the existing dead batteries instantly drag it down.

You'd be better off spending the money on a real charger, or jump the chassis battery with your car and jumper cables. Once the engine is running, then you can start your genny.

If your chassis batteries are dead as well, you are going to need a charger on them. Don't know what your coach has as a chassis battery maintainer. It might be an amp trickle charger, or perhaps a 15 amp-l-start that will feed from your house batteries once they get charged up high enough. Or, you could have nothing that charges your chassis battery.
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Old 12-27-2016, 12:39 PM   #13
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Quote:
Originally Posted by Racklefrack View Post
To be clear... I have no idea if this is how it's wired or not - I'm completely guessing in the dark without the necessary expertise to back it up. But the chassis batts are too dead to light up the dash and the house batts are too low to boost it.

Wired wrong or not, the system has always worked perfectly UNTIL I forgot to keep the batteries charged by running the generator a couple hours a day... hence needing the right size jump pack to get 'er started
just basing my reply on what you said in your post is all. personally rather than waste fuel and generator wear and tear I would make sure both set are 100% charged and simply disconnect them(what I do) that ends the delema

I will also opine that the reason your start batterys are dead is because your constantly starting your generator and most likly does not charge your chassis batterys
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Old 12-27-2016, 12:42 PM   #14
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Originally Posted by Kiawah View Post
Depending on the size of your battery banks, it's potential that little starter pak does little, as the existing dead batteries instantly drag it down.

You'd be better off spending the money on a real charger, or jump it with your car with jumper cables.
A "little" starter pack is exactly what I'm trying to avoid buying, but I didn't think trying to jump it off my car was a good idea... it just seemed like it'd be too big a draw on an automotive alternator / battery.

That was just an uneducated guess on my part, though. Anyone else think jumping it off my car would be ok?

Thanks for the input Kiawah
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