# Treadmill motor generator help



## Badfish740 (Aug 24, 2015)

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.


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## Jags (Aug 24, 2015)

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.


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## notshubby (Aug 24, 2015)

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.


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## Badfish740 (Aug 24, 2015)

Jags said:


> 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:

http://www.dbelectrical.com/p-4418-...&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?


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## Jags (Aug 24, 2015)

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.


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## Badfish740 (Aug 24, 2015)

Jags said:


> 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...


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## Jags (Aug 24, 2015)

Badfish740 said:


> 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.


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## notshubby (Aug 24, 2015)

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.


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## notshubby (Aug 24, 2015)

Jags said:


> 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.


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## Jags (Aug 24, 2015)

Jags said:


> 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.


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## notshubby (Aug 24, 2015)

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?


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## notshubby (Aug 24, 2015)

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


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## Jags (Aug 24, 2015)

notshubby said:


> 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.


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## notshubby (Aug 24, 2015)

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.


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## notshubby (Aug 24, 2015)

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


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## notshubby (Aug 24, 2015)

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


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## Badfish740 (Aug 24, 2015)

notshubby said:


> 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?









notshubby said:


> 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.


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## notshubby (Aug 24, 2015)

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


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## Badfish740 (Aug 24, 2015)

notshubby said:


> 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?


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## notshubby (Aug 24, 2015)

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


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## Badfish740 (Aug 24, 2015)

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.


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## notshubby (Aug 24, 2015)

Badfish740 said:


> 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.


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## xman23 (Aug 27, 2015)

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.


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## begreen (Aug 29, 2015)

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?


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## xman23 (Aug 30, 2015)

begreen said:


> 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.


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## Bret Chase (Aug 30, 2015)

xman23 said:


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



I think most of the electric only lakes has more to do with an IC outboard cooling/muffling it's exhaust with lake water than noise...


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## begreen (Aug 30, 2015)

Than makes sense, thx.


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## Badfish740 (Aug 31, 2015)

Still weighing the options on this one-there are a few:

One unregulated 12V alternator tuned to 48V via RPM
Run two 24V alternators in series
Run two Dodge military truck generators (they had 24V generators because the rest of the vehicle electrical system was 12V) in series



begreen said:


> 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?



The goal is really to have a "hybrid."  Electric is great when cruising slowly (and quietly), especially for wildlife watching along the shoreline, etc...  Getting across the 2 mile wide lake with a breeze in your face is a different story.  What I want to be able to do is the following:

Start the trip with fully charged batteries/a full tank of gas in the generator
Run the generator for the trip across the lake with the generator supplying most, if not all, of the power required by the electric outboard
Rely on batteries only once we get to our favorite cruising area
Run the generator for the way back (or not) depending on how depleted the batteries get



xman23 said:


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



At least according to the way the NJ Division of Parks and Forestry (the governing body that controls the lakes in question) words their regulations, it's not expressly prohibited (the rules say "No gas _outboards" _with no further elaboration), but, I would imagine that if I were caught running such a setup I would get a ticket.  This is why I'm looking for the smallest and quietest option for power generation.  A little 3.5HP OHV engine with a large generator type muffler would be very quiet and easy to conceal.  Most of these lakes don't have much of an enforcement presence anyway-with state budget cuts, etc...there might be one ranger at any given park who spends most of his time patrolling dry land and rarely, if ever, actually gets out on the water.  

I'm not looking to be a scofflaw, either, I'm just trying to get around rules that don't make it very easy for a family of four to get out on the water on some of the nicest lakes in NJ.  The electric only rule severely limits the size of your boat, your motor, and your range, if you use a conventional trolling motor and a 12V battery or two.  I'm running a 48V 1200W motor coupled to the leg of an old outboard, so I'm swinging a 6.25" pitch 3 blade prop at 1500 RPM, which can move a 16' boat at a pretty decent clip, but only for about an hour running full out (5-6 knots).


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## Snagdaddy (Aug 31, 2015)

The sound of your generator will attract attention legal or not.  Parks and Forestry Law Enforcement will harass you in spite of your legality, this is to be expected on state property in New Jersey, unfortunately.  If they don't like your setup they will find missing life preservers or something else to punish you.

     As you are considering buying a quiet generator to provide constant recharge of your battery, seek an option that will not overload the battery when just charging and not actually under way - then be able to flip to full generator 12v power to the batteries when under way.

     Perhaps an extra excuse for running the generator is in order.  Like to run a 12v powered cooler to keep your child's insulin cold.  Or a 12v fan to keep your wife cool because of some medical condition.  Or to recharge your phone because of your really important job.


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## xman23 (Aug 31, 2015)

Snagdaddy, your absolutely correct. Sad to say, I've seen them in action.. I wouldn't go near my boat when there present. And I don't have anything wrong. 

Badfish, it sounds clear to me, they are banning direct gas outboard motors in the water. Have you ever seen the oil that is put into the water from the exhaust of a 2 cycle outboard. I don't think they are restricting the way you are powering the electric motor. The battery, generator, fuel cell, solar cell, etc produce the electric power to run the motor.


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## Dr.Faustus (Sep 15, 2015)

this site should help you. I made one long ago before I could afford a real generator. Worked pretty good, kept the important stuff running during power outages like the sump pump, fridge etc.

http://theepicenter.com/blog/generator-lawn-mower-horizontal/


it uses the gm alternator and goes into great detail on how.


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