Running a 24V motor on a 12V boat system

nop

Recruit
Joined
Dec 15, 2016
Messages
1
I'm trying to design a jigging machine for a fishing boat, using a RaspPi as the controller. (A jigging machine jerks a 1kg lure up and down near the sea bed, and pulls in a fish when it's hooked.)
The motor I'm hoping to use is here: http://www.kynix.com/Parts/3227730/34KM-K122-99W.html and the supplier recommends I recommends I use a 24V supply.
However, the boat I want to fit the machine to has only 12V. I'm trying to assess the pros and cons of different approaches.
The simplest solution is to just use a 12V supply to the motor. I understand I'll need thicker wires to supply this. I'm thinking that using 12V will generate more heat and produce less torque. There will be times that the machine will need to pull up several fish at a time from 50m deep - say a 20-30 kg load. And sometimes the hook will snag the bottom. I'll include a current monitor, so I could limit or cut the supply when there is too much load. I don't know how often this might happen till I try it though, and how inconvenient it would be.
I've ruled out having 2 batteries, in parallel when the engine is running and in series when the engine is stopped, using solenoids to switch - the engine is often left running while the boat is fishing, as it needs to continually drift with the tide/wind, then motor back up to the spot where the fish are.
So I think the only other option is to buy a second battery and wire in series, swap the 12V alternator for a 24V alternator, and have something that supplies 12V from the 24V for the GPS, radio etc.
Naturally, I'd favour the first option, but I wonder how important a 24V supply would be for the jigging motor, and how much we'd lose out going with the 12V option.
Thanks for any further input on my inputs quandary.
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
If the motor is designed to run on 24 volts it will not perform well at all on 12 volts. After all, that's why it was designed to run on 24 volts. Adding a 24 volt alternator rather than replacing the 12 volt makes more sense. You do not endanger any 12 volt stuff and the 24 alternator would take care of the 24 volt system. Yes, some fabrication is required for the alternator mounts but that's not rocket science. If you really intend to swap the 12v for a 24v alternator, you can still get 12 volts from the 24 volt system as follows -- BUT PAY ATTENTION: Do this wrong and you fry your 12 volt stuff.
1) Determine which of the two batteries will have the NEGATIVE connection from the jigging motor. That terminal will now serve as the ground (negative) for all 12 volt accessories.
2) Connect the POSITIVE lead for all loads to the POSITIVE terminal on the battery to which the POSITIVE lead from the jigging motor is connected. This will be the OTHER battery.
 

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,605
:welcome: aboard nop to iboats. Nice to have a new member.

While I am not sure what you are trying to accomplish, I do know about electronics. And there is a simpler was to run your idea. You can always build a voltage "boost" converter circuit to supply 24 volts to your setup. It is not very hard to do and you could even find such a circuit built already to supply 24 volts from a 12 volt source. Then everything else would be the same. JMHO
 

fishrdan

Admiral
Joined
Jan 25, 2008
Messages
6,989
How much current do the motor(s) draw?

I like gm280's idea of using a step-up converter as it will provide "24v" the motor and controller most likely need to run off of. If you go with batteries in series, it will be something like 25-28V, which the controller and motor may not like.

IF... the motor and controller can handle the higher voltage, you could add another battery in series along with a MinnKota Alternator Charger. The Alternator Charger will keep the second battery topped off while the engine is running.

Either way, you may have to upgrade the alternator so your idle charging current is higher that than the stock alternator. That puts us back to my first question, how much current do the motor(s) draw?
 
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