Treadmill motor generator help

[Badfish740]

I've got three permanent magnet DC treadmill motors laying around. These seem to be big with the DIY energy crowd for building wind turbines, but that's not what I want to use them for. I'm wondering how much power I could get out of them when driven by either a 3.5 or 6.5 HP Predator (Harbor Freight) engine. This guy strapped a similar motor to an old (and probably worn out) 3HP lawn edger and with a proper pulley setup is getting 12V/16A:

http://mdpub.com/generator/

Is there any reliable way to predict how many amps I could get out of a motor based on RPM/HP/VDC ratings? For example, I know that if I connected the motor to a 3.5 or 6.5HP engine, I could get 48V simply by fitting the proper pulleys to make sure that the motor is turning at 2240 RPM, but how many amps? What I'm trying to figure out is whether or not I could run a 48V electric outboard drawing 27A via a small DC generator mounted elsewhere in the boat, or at least use the generator to supplement a 48V battery bank so that the boat could run all day.

I've seen "cheater" setups like this before on electric only lakes. Basically what guys do is bring a very small generator with them like the really quiet inverter models people take camping. They run their batteries down and once they're out in the middle of the lake or they beach somewhere for lunch they run the generator top up the batteries or on sophisticated systems, they run the generator while underway so that the motor is pulling power from the generator with the batteries acting as a buffer. The thing is, they're generating AC power from the generator and having to use a power converter to charge the batteries/run the motor. Seems pretty inefficient, and that just generating DC from the get-go would be much better. I'm hoping that some of the electrical wizards here can help me out.

 

[Jags]

Hmmm...I understand the want of DC without a converter, but there are some pretty good examples of already built units that have done a nice job for a long time. Think one wire GM alternators. Darn near everything you need in one nice neat package than can easily be capable of the amperage you are looking for and without the finicky voltage issues you will have with your DC motor.

 

[notshubby]

doesn't have to be one wire either just one of the older alternators with internal voltage regulator. run a switch to power your field windings. and they are a dime a dozen.

 

[Badfish740]

Hmmm...I understand the want of DC without a converter, but there are some pretty good examples of already built units that have done a nice job for a long time. Think one wire GM alternators. Darn near everything you need in one nice neat package than can easily be capable of the amperage you are looking for and without the finicky voltage issues you will have with your DC motor.

OK, school me on a few things here. Let's use this alternator as an example:

(broken link removed to http://www.dbelectrical.com/p-4418-new-high-output-chevy-one-1-wire-alternator-105-amp-10si-se.aspx?CAWELAID=130000240000000177&CAGPSPN=pla&gclid=CMSKycHrwccCFYoTHwodYfcD_w)

This guy puts out a whopping 105 amps @ 12V for $63-not bad. However, I would need 48V to run the electric outboard (think trolling motor on steroids)/charge the battery bank, so what would I need to do in order to get the 48V?

 

[Jags]

Parallel run the 12V (from alternator) to each of the 4 batteries. If the batteries are fairly well matched, each will pull about 25 Amps from the alternator (max). You would be feeding 12V batteries, not a 48V motor.

 

[Badfish740]

Parallel run the 12V (from alternator) to each of the 4 batteries. If the batteries are fairly well matched, each will pull about 25 Amps from the alternator (max). You would be feeding 12V batteries, not a 48V motor.

OK, I'm following, but would it be possible to the generator charge the batteries in parallel while they are running the motor wired in series? I have seen setups like this, but I have no idea what kind of hardware they're using, etc...

 

[Jags]

OK, I'm following, but would it be possible to the generator charge the batteries in parallel while they are running the motor wired in series? I have seen setups like this, but I have no idea what kind of hardware they're using, etc...

Technical answer is yes. Basically you can view it as two separate circuits. The 12V charge is isolated "per battery". The 48V is a completely different daisy chained (called series) circuit.
In this type of setup you really do want "matched" batteries so that each battery is "treated the same" from the alternator.

Un-technical answer is...I would be more inclined to use this, as you say, while beached or when sitting (not running the 48V motor). There is just less of a chance of something becoming unstable with the charge circuit. It really shouldn't happen, just like when you are driving down the road and your alternator is charging the battery as well as running the electric load of the vehicle, but you have 4 times the chances with 4 batteries in series.

 

[notshubby]

48 volts changes the entire spectrum. its not a commonly used voltage in anything that isn't plugged in to charge like electric forklifts. but even with the treadmill motor your asking a lot of it spinning it at 2200 rpm might produce the 48 volts but not much amperage. and its probably gonna run VERY hot. I know that you can take out the voltage regulator on some of the bigger gm alternators (think cs144) run power straight to the fields (or in my case through a potentiometer) and produce up to 80 or 90 ocv . but then you have to take the wild 3 phase straight out of alternator and run it to a bigger bridge rectifier. this is how I built the onboard welder in my jeep. but I pretty much just copied someone elses design. not sure if it would work in your application. but might be worth looking into.

 

[notshubby]

Parallel run the 12V (from alternator) to each of the 4 batteries. If the batteries are fairly well matched, each will pull about 25 Amps from the alternator (max). You would be feeding 12V batteries, not a 48V motor.

never thought of that sounds like it would work.

 

[Jags]

Technical answer is yes.

WAIT A MINUTE. I Think I am wrong on this one. You won't be able to have the series circuit in place when you are charging the batteries. In the series circuit the neg of one battery is electrically the same as the positive node of the next. The alternator would be shorted at this point.

STRIKE VIRTUALLY EVERYTHING I SAID ABOVE FROM THE RECORD.

Sorry for the confusion but as I was talking this through in my head, something clicked.

 

[notshubby]

alternators charge 2 or more batteries on big trucks. and if I remember right didn't a lot of the old macks use 4 big 6 volt batteries to make the 24 volts?

 

[notshubby]

ohh wait they used 24 volt alts to charge the whole bank.

 

[Jags]

alternators charge 2 or more batteries on big trucks. and if I remember right didn't a lot of the old macks use 4 big 6 volt batteries to make the 24 volts?

I think you will find that those are 24V alternators.

 

[notshubby]

your absolutely right however he can still charge while not running by isolating the batteries. but probably the simpler solution would be just use the inverter gen and a small 48 volt forklift charger.

 

[notshubby]

you could charge like jags suggested but would need diodes at every terminal in the charge series

 

[notshubby]

I don't know if something like this would work with your amperage.
http://www.amazon.com/Boost-Converter-Voltage-Regulator-Supply/dp/B00M2SB476

 

[Badfish740]

you could charge like jags suggested but would need diodes at every terminal in the charge series

In other words, to make sure that the wiring was a "one way street?" That makes sense. In this diagram where would the diodes be placed assuming the wires were actually run this way?

I don't know if something like this would work with your amperage. http://www.amazon.com/Boost-Converter-Voltage-Regulator-Supply/dp/B00M2SB476

As far as I can tell it only puts out 4A max. I think the alternator option with the diodes to isolate the two circuits would be the best. I could sell the two treadmill motors on Ebay (it looks like they sell for about $50) and put the money toward a brand new engine and alternator.

 

[notshubby]

well your drawing isn't right as it shows the batteries aren't connected in a series. sorry im not the best with the computer so I did a quick sketch. theres your series drawing

 

[Badfish740]

well your drawing isn't right as it shows the batteries aren't connected in a series. sorry im not the best with the computer so I did a quick sketch. theres your series drawing

Aha...I see where I went wrong, so regardless, in that configuration, where would the diodes go?

 

[notshubby]

I'm thinking lol. I might have to show my electrician at work and go over it with him. the way I was thinking might not work

 

[Badfish740]

I've been doing some poking around and it seems that it's actually not that difficult to modify an automotive alternator to output any voltage you want up to 100VDC or so. Still working through the details, but I'll post what I find.

 

[notshubby]

I've been doing some poking around and it seems that it's actually not that difficult to modify an automotive alternator to output any voltage you want up to 100VDC or so. Still working through the details, but I'll post what I find.

yep just take control of that voltage input to the field. anything that doesn't have avalanche diodes should work for your charging with the stock diodes.

 

[xman23]

Just another idea. If the goal is to have a electric trolling motor run all day, with or without batteries on the boat. A gas 1800 - 2000 watt 115 vac emergency power generator is big enough. Use a switching power supply, 115 vac to 48vdc to run the motor directly with no batteries. Or run a AC battery charger to charge the batteries and run the motor at the same time.

I have a champion inverter pure sine wave, about 1800 watt that I back feed my house with. It runs every thing in the house. Of course one large power item at a time.

 

[begreen]

I would think the running a genny would defeat the reason for a quiet battery powered motor. At that point why not just use a small gas driven motor like the little Honda 2.3 hp unit?

 

[xman23]

I would think the running a genny would defeat the reason for a quiet battery powered motor. At that point why not just use a small gas driven motor like the little Honda 2.3 hp unit?

BeGreen, I think the issue is the all electric lakes. But I wonder if the gas generator running the electric motor is a legal.