Does anyone know, or measured the cranking current inrush on a 32VDC DD 8v53? I'm potentially changing battery switches and want to ensure it can handle the current.

Thanks!

Steve.

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I am not sure if you are asking if the new switch, the battery,or the engine can handle the current in rush.

The batteries are good (4x 8D starting). I'd like to know the current rating (5min) and the inrush (10 sec) required to start the DD's. For instance, one switch has a continuous rating of 300A, a 10 min rating of 450A and an 10 sec rating of 1500A - would that work or do I need a more heavy duty switch?

Typically I would get a switch based on what the batteries are cappable of putting out, though with multiple 8D's the output poential would be huge. Do you use all 4 batteries when starting?

Check what it take to start one of your engines at a time, you do not start both engines at one time.  Then base your purchase on that as you heavy draw for 10 seconds, you should only use one of the batteries as a starter battery.

Yep. Since this boat is still 32V, it has 4x 8V batteries for start and 4x 8V batteries for the house. I would love to measure the current with my meter, but the boat is on blocks - so I was hoping someone had a spec sheet that spoke to that number. I found the service manuals on the boat last weekend, I'll go through those when I get back to the boat to see if they detail it.

Mike H said:

Typically I would get a switch based on what the batteries are cappable of putting out, though with multiple 8D's the output poential would be huge. Do you use all 4 batteries when starting?

Does your manual list the draw of the engines to start?

Ah, so these batteries are run in series. In that case the amperage output is equal to what one battery puts out. Being in series only increases the voltage, not the amperage.

Steve Valvasori said:

Yep. Since this boat is still 32V, it has 4x 8V batteries for start and 4x 8V batteries for the house. I would love to measure the current with my meter, but the boat is on blocks - so I was hoping someone had a spec sheet that spoke to that number. I found the service manuals on the boat last weekend, I'll go through those when I get back to the boat to see if they detail it.

Mike H said:

Typically I would get a switch based on what the batteries are cappable of putting out, though with multiple 8D's the output poential would be huge. Do you use all 4 batteries when starting?

Do you know your starter motor model and manufacturer?  With that information you can look up the max draw of the motor and you will know which switch to purchase, we all talk about the engine but realize it is the starter motor drawing the current.

Not sure. I'll take a look when i get back to the boat.

The thing we have to remember here is Ohm's Law --- when voltage increases, amperage decreases. Steve's engines are 32 volts, so his amperage at this voltage would be nowhere near as high as it would be with 12 volts. For example, 500 amps @ 12 volts = 166  188 amps @ 32 volts. This is exactly why years ago auto manufacturers went from 6 volts to 12 volts. Because the current was halved, they could use lighter wires in the car. What part of capitalism don't you understand :-)  ??  Same thing in 32 volt boats, lighter wire gauges. What I don't understand however is 32 volts -- This is a bastard voltage compared to 36 volts. Every member with a 32 V boat pays the price for 4 oddball 8 volt batteries to put in series to generate 32 volts.

Another mystery to me --- some 47's with 424 cu.in. 8V53 Detroits have 32 volts, while the 785 cu.in Cummins VT8-370M's in our old 47 did nicely on 12 volts. Did not need any preheat, rolled over easily, and popped right off when you hit the key. Ah, the mysteries of life :-)

Oops ! Math error in above, just spotted it. 500 amps @ 12 volts is the equivalent of 188 amps @ 32 volts.

So I was gonna say the 300A would be fine. Dick so eloquently proved it too!  =)

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