Charging a trolling motor while running it

[rebocc]

Ok, here's one for the electronics guys:

I converted a 16 foot boat to electric by taking out the motor and putting in a MinnKota 36V 101#motor on a home-made rudder. Three 12V batteries. So far I use it for puddling on small lakes, and it works great - suits my needs, nice and quiet, no hassles starting motors.

I have an onboard 3-bank charger (3 x 5amp), so on land, I just plug it in to charge.

I would like to use it for overnight camping and fishing, and also for weekend trips on the Trent Severn system here in Ontario. Thinking about extending the range.

I'm thinking a 2 KW generator should more or less keep up with battery discharge. The generator could be installed in a ventilated styrofoam-lined box, to keep it quiet.

Can I run the generator to charge the batteries while the trolling motor is in use? Or do I need to wait until I'm done running, and then run the generator? I know a car battery runs stuff (radio, headlights, etc) while being charged by the alternator.

Looking for knowledgeable responses, not just "oh, that sounds bad".

Cheers and thanks in advance!

 

[kahuna123]

Re: Charging a trolling motor while running it

At this point go but a very small 4 stroke outboard.

 

[rebocc]

Re: Charging a trolling motor while running it

Thank you for taking the time to reply, but i have no interest in a gas motor.

The question was: Can I charge while running my motor, or do I need to stop it to charge?

Either is ok with me, but I would like the flexibility of charging while running...

Any answers appreciated.

 

[MH Hawker]

Re: Charging a trolling motor while running it

Yes I dont see way it wouldn't the gen and charger don't care it its being used or not, how ever its not a good way to do things unless its a correctly installed marine gen set.

 

[TerryMSU]

Re: Charging a trolling motor while running it

Unless the generator is designed to be explosion proof, using it in a boat without forced ventilation can be a big no-no. Depending on where you are going the coast guard can really get at you for that. That said, in my open boat, I would probably risk it. As far as running the charger while running the TM, I can't imagine any issues.

TerryMSU

 

[rebocc]

Re: Charging a trolling motor while running it

Unless the generator is designed to be explosion proof, using it in a boat without forced ventilation can be a big no-no.
TerryMSU

Good point. Was thinking to hook a blower up to the DC output of the generator, to keep fumes out of the boat and keep clean air in the generator box whenever it's running.

Thx for the responses. I'll do some research on marine generators.

 

[dwparker99]

Re: Charging a trolling motor while running it

Curious as to why you think "a 2 KW generator should more or less keep up with battery discharge." How do you plan to charge, by using the onboard charger or getting a generator with a built in charger?

 

[rebocc]

Re: Charging a trolling motor while running it

Curious as to why you think "a 2 KW generator should more or less keep up with battery discharge." How do you plan to charge, by using the onboard charger or getting a generator with a built in charger?

Well, it's based on the following rough calculation - correct me if I'm wrong:

101# trolling motor is roughly 1 or 2 hp. Let's say 2 hp for a high-end guess. I think it's less though.

2 hp = approx 1500 watts

So if the motor uses 1500 watts, a 2kw generator should be able to keep up with it, or a 3kw generator running at half speed for efficiency (and some extra capacity).

That's assuming the generator is AC, and the generator is plugged into the onboard charger. I think the wiring would get too confusing if I had 3 batteries wired with an onboard charger, and also wired with a generator charger. I'm looking for a setup that's wired properly and permanently, and doesn't require disconnecting wires.

As I mentioned, I'd put the generator in an insulated ventilated box by the transom, with a blower running off the generator's DC output.

 

[dwparker99]

Re: Charging a trolling motor while running it

It seems like the onboard charger will be your limiting factor. At max thrust, your TM will be pulling ~45 amps from each battery. If your onboard charger is supplying 5 amps per bank, you have a deficit of 40 amps. Even at its lowest setting, your TM will probably be pulling some amps from the batteries even if the generator is running. To make use of the power the generator can supply, you would have to upgrade your onboard charger.

 

[TerryMSU]

Re: Charging a trolling motor while running it

It seems like the onboard charger will be your limiting factor. At max thrust, your TM will be pulling ~45 amps from each battery. If your onboard charger is supplying 5 amps per bank, you have a deficit of 40 amps. Even at its lowest setting, your TM will probably be pulling some amps from the batteries even if the generator is running. To make use of the power the generator can supply, you would have to upgrade your onboard charger.

45 Amps * 12 volts = 540 watts. You do not need a 2KW generator. 1000 watts is way more than enough. Since you will not be running full speed most of the time, even 500W would likely be enough. The charger will need to be fairly beefy to supply 45 amps, but again, the battery will smooth that load out.

oops, I just realized it is 36 volts. 1620 watts. 2 KW gen is about correct.
TerryMSU

TerryMSU

 

[glenn property of pam]

Re: Charging a trolling motor while running it

36v alternator belt driven by small engine might work. this would have less problems than a 110v generator and a battery charger thats not capable of the ampage required and the electrical safety required.

 

[dlngr]

Re: Charging a trolling motor while running it

Why will you run a gas generator,but not a gas outboard? Think of the weight you'd save by using a small [5 or 6 hp]outboard.

 

[dwparker99]

Re: Charging a trolling motor while running it

If you are going to charge with a generator and onboard charger while running your TM, make sure you understand your charger's charge algorithm. There are scenarios you can get into where your generator will be running but you onboard charger is not charging at all or is only putting out 1-1.5 amps.

 

[Bondo]

Re: Charging a trolling motor while running it

Well, it's based on the following rough calculation - correct me if I'm wrong:

101# trolling motor is roughly 1 or 2 hp. Let's say 2 hp for a high-end guess. I think it's less though.

2 hp = approx 1500 watts

So if the motor uses 1500 watts, a 2kw generator should be able to keep up with it, or a 3kw generator running at half speed for efficiency (and some extra capacity).

That's assuming the generator is AC, and the generator is plugged into the onboard charger. I think the wiring would get too confusing if I had 3 batteries wired with an onboard charger, and also wired with a generator charger. I'm looking for a setup that's wired properly and permanently, and doesn't require disconnecting wires.

As I mentioned, I'd put the generator in an insulated ventilated box by the transom, with a blower running off the generator's DC output.

Ayuh,.... This is a pretty ridiculous idea,...
Just because yer generator is puttin' out 2000 watts, AC, don't mean yer battery charger is puttin' out 2000 watts, DC...

Yer talkin' 'bout convertin' gas to electrical AC power, then to DC power, then to prop thrust...
Anytime energy is converted, there's a parasitic power Loss...

Boltin' on a small outboard will be Much more Efficient, 'n Quieter, 'n Safer...

 

[Rancherlee]

Re: Charging a trolling motor while running it

Still trying to wrap my head around this also, a 2-2.5hp outboard at 1/2 throttle will be quiter than the 3.5hp 1500w generator required to charge the batteries. And if to go on electric only lake like those in some areas the gas generator violates that rule anyhow. I use to use a 45# troller and single big battery for backwoods fishing and now use a 6hp with a 3 gallon as its LIGHTER than the troller/battery combo and lasts longer. Also that small generator isn't going to tolerate the heat being boxed in to reduce noise and you STILL have to pull a recoil to start it.

 

[dwparker99]

Re: Charging a trolling motor while running it

Dang it, I wonder where the OP went? Maybe he is confused as to how we can look into our crystal ball and determine better than he what his needs are. Maybe he doesn't understand why we keep pushing a gas motor even after he has twice told us he is not interested in a gas motor. Maybe he took offense in us calling his thinking "ridiculous." It seems he is happy with his setup and would like to charge the batteries for weekend trips with a generator and charger and also use it to extend his run time while on the water if possible. Can we help him with that or is our knowledge limited to "get a gas motor?"

 

[glenn property of pam]

Re: Charging a trolling motor while running it

my be this should be ...i have a generator that i use for camping can i stick it in the boat and charge the batterys while on the water

 

[Silvertip]

Re: Charging a trolling motor while running it

So you really intend to run a generator (115 volt output AC) to power a 3 bank battery charger? The concept is sound except that 101# troller sucks 46 amps at 36 volts. The maximum output of the charger, regardless what you power it with, is 15 amps so you are losing ground at 46 amps with no chargers, or 31 amps with the charger. So the practical way to look at this is that at full speed the generator can only "prolong" run time by less than 1/3 since the batteries do not charge on a linear curve. If you intend to charge the batteries from a 12 volt tap on the generator make darned sure you take a fire extinguisher with you. You cannot charge a series string of 12 volt batteries from a singe 12 volt source. You would have to charge each battery individually via some sort of switching system. Even then, you must also switch grounds - the reason for which has been discussed to death in these threads.

 

[rebocc]

Re: Charging a trolling motor while running it

45 Amps * 12 volts = 540 watts. You do not need a 2KW generator. 1000 watts is way more than enough. Since you will not be running full speed most of the time, even 500W would likely be enough. The charger will need to be fairly beefy to supply 45 amps, but again, the battery will smooth that load out.

TerryMSU

TerryMSU

That's correct, except that I think it's 45 amps X 36 volts, which is about 1600 watts.

 

[rebocc]

Re: Charging a trolling motor while running it

So you really intend to run a generator (115 volt output AC) to power a 3 bank battery charger? The concept is sound except that 101# troller sucks 46 amps at 36 volts. The maximum output of the charger, regardless what you power it with, is 15 amps so you are losing ground at 46 amps with no chargers, or 31 amps with the charger. So the practical way to look at this is that at full speed the generator can only "prolong" run time by less than 1/3 since the batteries do not charge on a linear curve. If you intend to charge the batteries from a 12 volt tap on the generator make darned sure you take a fire extinguisher with you. You cannot charge a series string of 12 volt batteries from a singe 12 volt source. You would have to charge each battery individually via some sort of switching system. Even then, you must also switch grounds - the reason for which has been discussed to death in these threads.

You can't really compare Amps at different voltages. A battery bank at 36 volts X 45 amps is similar to 120 volts X 15 amps.