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Discussion Starter #1
Well . . . this is a little different from the auxiliary power issues that most of you have dealt with, but I'm sure some of you will understand my needs better than I do. I have spent hours researching and I seem to be going in circles, so I would welcome suggestions.

I am about to install a compact hydraulic crane on my PM chassis cab (flatbed). The crane will be powered by a 2Hp 12V hydraulic pump. The pump motor will draw about 130A. That is obviously a significant load, but it will only run in ~5 minute spurts. My typical use may be a few times per month, with each use being about three 5 minute spurts with 5 minutes of rest between. My use will NOT be like RV use--running a refrigerator 24/7, etc.

The options I am considering are:

1--Connect the pump motor directly to the starter battery. If the battery alone doesn't supply enough power for my usage, I can run the engine while using the crane. (My PM has the 220A alternator.) Positives: simple, cheap, doesn't add extra weight. Negatives: running engine, hard on battery(?). If I go this route, I will consider a dual-purpose battery when my current battery wears out.

2--Install an isolator and auxiliary battery (or 2 6-volt batteries in series) and run the hydraulic pump off of the auxiliary battery. Positives: less need to run engine, no strain on starter battery. Negatives: more complicated installation, more maintenance, additional cost, additional weight.

If I could get away with option 1, that would be preferable (K.I.S.S.). Any suggestions? Is there another option I am missing?

Thanks
 

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2016 136WB low roof diesel, converted to an RV by Sportsmobile, TX
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Running that pump for 5 minutes will be roughly like running your starter for about a minute (starters are around 300A or so). Normally, in a vehicle you would then run the engine for a relatively long time to replenish the battery after, but you have a pretty short cycle time.

Using the main battery is doable, but I would suggest having the engine running when using the lift.
 

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We concur that use of the starter battery with engine running should be fine. The only caveat being, what is your alternator's output capability at idle? The goal would be to have your alternator, not the battery, supplying the required 125 amp current - - no stress on the battery, no discharge of the battery.
 

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Discussion Starter #4
what is your alternator's output capability at idle?.
Good question. I was thinking that the alternator's output would adjust to the current being drawn, but I guess I didn't really think that through.
 
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