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Old 28 March 2014, 08:15   #1
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Water-dragged Battery Charge generator?

Hi all,

Wondering if anyone knows of a battery charge-generator that can be towed behind an inflatable?
Have both an electric and gas engine and would like to be able to charge the battery while trolling with the gas motor.

Any ideas welcome. Solar panels have already been researched.

Thanks,

Scott
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Old 29 March 2014, 04:37   #2
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Erm.... a charging circuit on the gas motor might be a better idea.
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Old 30 March 2014, 18:24   #3
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I have read about them used on sailing yachts for long distance cruising , not sure how great a charge they will give though for short distance usage.as Nos said you may be better using the outboard for charging .
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Old 31 March 2014, 05:09   #4
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To answer your question without opinion:
Ampair aquair 100 is a towed generator for yachts
Ampair Wind, Hydro and Packaged Power specialists +44 (0) 1258 837 266 | Aquair 100
They are designed for charging sail boats at between 4 and 12kts
Max output is little below 6 amps, at around 7kts, (~75 watts)
A typical 55lb thrust electric trolling motor will draw around 50 amps at full speed (600W). Assume you will use close to full power most of the time - average 500W draw - you will have to cruise for around 7 hours to charge the battery enough for 1 hour use.
Some more realistic scenarios: If you are just trolling around, perhaps you need to use the motor for around 20 minutes, in which case a 2.5 hour journey at 7 kts would give you enough charge (probably).
To put it yet another way, a 30 minute cruise to your fishing site (at 7kts max!) would give you just over 4 minutes extra on the electric motor.
Compare this to a 70HP petrol outboard with a 25A alternator. A run of under 2 hours at wide-open-throttle would give you 1 hour on the electric motor, or, a 30 minute journey to your fishing site (at wide open throttle) would give you an extra 18 minutes on the electric motor.
Lots of assumptions here - assume the actual figures could be 20% lower or so with losses due to temperature, gauge of cable, corrosion etc etc

To answer your question with an opinionated answer:
If your engine has a charging coil /circuit you would be crazy not to use that instead of the horribly inefficient, complicated, expensive, faff-tastic water-towed generator. If your engine doesn't have a charging coil it may still be cheaper to fit one rather than buy the water towed generator. Even after this, you're really not adding a lot of extra range to your electric motor and would be restricting yourself to either journeying at 7kts (towed generator) or full throttle (engine alternator) to get any meaningful(!) extra charge into your battery.
If you are going to the trouble of carrying all this extra generator gear, You'd get more range by just carrying another deep cycle battery instead, and it would be cheaper. If your journey from home to the boat ramp takes some time, you might consider a caravan-style hookup to top-up the batteries from your tow vehicle electrics, which might give you the same few extra minutes run-time on the trolling motor.
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Old 31 March 2014, 08:46   #5
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Quote:
Originally Posted by Nightfisher View Post
Have both an electric and gas engine and would like to be able to charge the battery while trolling with the gas motor.
Am I missing something here?

"trolling with the gas motor" - what do you use the electric for? I assume there are times when you need to troll in complete stealth? If so for how long?

In which case would a super quiet (read: new 4- stroke!) 1 or 2Hp gas burner be a more viable option? - A lot of new 4 strokes you can't hear at or around tickover....
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Old 20 April 2014, 08:31   #6
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Quote:
Originally Posted by 9D280 View Post
Am I missing something here?

"trolling with the gas motor" - what do you use the electric for? I assume there are times when you need to troll in complete stealth? If so for how long?

In which case would a super quiet (read: new 4- stroke!) 1 or 2Hp gas burner be a more viable option? - A lot of new 4 strokes you can't hear at or around tickover....
The cost to convert my outboard' electrics to produce just 5 amp charge output is about 300.00. Solar panels to little current to recharge batteries. But I had heard where an old electric motor was easily converted into a charger that will give 6-9 amps. Just wondering if anyone had heard of it or know where I can find info on it?

The idea is to used the electric where possible and the 10 horse to get around and to charge the batteries if I can find a information on convertin an old electric into a generator.
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Old 20 April 2014, 09:00   #7
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Look at the numbers- is it really worth it?

6-9amp charge rate. 30 minutes of running the engine ( assuming 100% efficiency) gives you a measly 4-6 minutes of extra run time on the electric outboard
Plus you have to carry the weight of the motor and whatever homemade arrangement you have to make it turn, if you aren't buying the engine charging kit ( which is effectively the same innards as a motor!)

Why not get another battery -
A small car battery will give you SIXTY minutes of extra runtime without the faff- and you don't need to run the engine at all!
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Old 20 April 2014, 09:10   #8
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By the time you've waterproofed it, or replaced it several times you'll find that hunting down the charging kit for the outboard from a breakers will be far less hassle and probably cheaper.
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