Treadmill DC moter for battery charging

I have had this 2hp treadmill motor laying in the shop for a while now. Originally was thinking wind generator but my location is not so great for that. I don’t think I have enough head in the creek . Steve’s challenge got me thinking about it again. Has anybody used one of these as a generator? What kind of controller would be required to charge a small battery bank? How fast would one want to spin one? The one I have is 130 volts , 17amps 2hp. I know little to nothing about generating ac or dc power other than I need to know. Would here be any benefits of using this over a regular automotive alternator to charge 3 12 volt AGM batteries?

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Hi Jim, glad you separated it out from Steve’s thread. It will be good to keep that one clean.
I have turned one of them before. The advantage over a regular alternator will be the savings you will get in not having to power the field; it being replaced by the magnets. The downside is you give up control of the field so you must control it’s charge rate yourself. First thing to do would be to determine what kind of DC motor you have. How many wires come out of it? That will tell you how many phases it’s wired for. When you turn it you will be generating AC current. The faster you turn it the higher the voltage and current . You must use diodes to control the alternating current then feed it into a voltage regulator so that high voltage does not fry the batteries… Lots of fun…


Go to Missouri Wind and Solar and look their charge controllers. These will take wild AC and convert it and control charge rates.

The advantage of this is AC can be carried a longer ways with less expensive cable. So you can have your batteries stored remotely.


thanks for the response David. So if I am generating AC power are the cycles regulated by rpm and can the power be used as AC rather than convert it and then convert it back? kind of sounds like with my limited knowledge of electronics at this time I would be better off with the car alternators . What alts work best? I have several. GMs from 70’s 80’s and 90’s and a couple from dodge vans even with them I an not sure at what rate to charge. I sure would hate to ruin my batteries but need to be able to charge them in a grid down situation. I have a couple small Honda 3.5hp 4 strokes a small Kawasaki 4 stroke that had carb issues would be my first choice if it is big enough. It seems I seen a chart recently with speeds and efficiencies.

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Thanks for the link Matt. A controller is not in my budget at this time. I keep my batteries in my attached garage at this time. my breaker panel and inverter are there too. makes it easy to get power to freezers and well pump. Never had to use any of it yet. Longest power outage here in the 15 years I been here was 20 minutes. The guy who owns the power co lives just after me on the line.

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Depending on where you plan on putting the generator, this will be very cheap compared to the cost of the heavy gage cable you would need to carry DC to your battery bank.

There are other chargers on the market, try Ebay and Amazon for a small wind turbine charger. That was just an example, its what we have sourced and is supposed to be one of the best ones out there.

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I agree with Matt. There are many small wind turbines with built in voltage regulators just turn them with a motor. When I say ac I mean wild ac… often 3 phase not even sure of the frequency…
If you want to turn a regular alternator your goal is to acheive a charge rate of 10% of the battery amp capacity. Lots of videos of how to out there. Not sure the ideal charge rate of AGM… just stay away from the one wire self exiting types. Uhg too late to type…


Thanks guys , Cabling I have, money I don’t so it will have to be an alt or nothing at this time. Batteries are 77.8 amp houres each.

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Now more awake… AGM sealed batteries are supposed to take charge better then lead acid looking it up they are recommending between c3 and c5 so between 40 and 70 amps if all three are connected in parallel. For the level of capacity you have best to think of them more as a buffer then a power source. Choose a load under your max charge rate, charge and use the load at the same time using an inverter as a go between. Sort of like a poor man’s inverter generator… Best I got, hope that helps more then it muddies the water…
Best regards David Baillie

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If you had 10 AGM batteries I would say charge them in series all the time.
This makes keeping a consistently even level of charge on them easier.

That could be a use for your motor…
Turn the machine at about 35% rated speed to get about 40 volts from it and monitor the charge current of the bank.
Use just enough current to get them to visibly off gas bimonthly.
Do a voltage check across the stack to see if you are dropping an equal amount of voltage across them.
This way your batteries will last longer and give you better service as they will all carry the load evenly in use.
Eventually if you do not do the equalization charge one battery will stay discharged and act as a drag on the rest of the system.

Now I just went to check the Trojan battery site to see their recommendation on the subject and they do not specifically mention AGM,
So that is also worth further investigation of how you should care for those specific types.

I am dating myself now because all my experience is with station batteries using lead acid or NiCad.
Reason is we always reconditioned our own flooded cell batteries, and I don’t think the thought of trying to do something with a gel filled type ever cross anyone’s mind.

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Wallace ,how do you recondition your lead acid batteries?

I don’t…

Send them out and the send some back to us.

I suspect the do a wash followed by a chemical cleaning and some tests.
What we get back are batteries that work with a significantly higher than normal failure rate and shorter life.

NiCads we did do now then,
They were just flushed and refilled with electrolyte.
Then they got a few hard fast charge discharge cycles to burn off any whiskers that formed in the plate ( I understand something in the chemistry of those old cells caused deposits called whiskers between the cells. ( caused by low current draws and shallow cycling ).

That’s all I can offer

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Jim - What is the model and brand of your batteries?

Thank you Wallace. Kyle I have always thought it shouldn’t be to hard to rebuild automotive batteries. My AGM’s are dynasty UPS300-12MR. I got them used for free and seem to be great batteries. At this time they are in the back seat of my car, charge as I drive. They power my laptop, internet ,and a LED bulb in a lamp. When I go to bed at night I Plug in my side by side fridge and the 3 of them and my car battery take it through the night. Still enough juice to start the car in the morning. I will be getting a charge controller this week. That will really help. Depending on cost may get a couple 240 watt solar panels as well.


Jim - This looks like the technical data sheet for your batteries.

Here is what I get out of that, as it pertains to charging.

Current Limit: “C/5 amperes @ 20hr rate”

Float Charge: “13.65 ± 1.5 VDC average per 12V unit”

Equalize Charge and cycle service voltage : “14.40 to 14.80 VDC average per 12V unit”

All of this is at the nominal battery temperature of 74F. If you will be charging them in significantly different temperatures, then you either need a temperature compensated charge controller, or you will have to allow for that manually.

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I don’t see where they mention the battery capacity at the 20 hour discharge rate in their literature. But you say the capacity is “77.8 amp hours each.” If this is quoted on the battery, then this is probably at the 20 hour rate (most deep cycle batteries are quoted at that rate).

Therefore, the maximum charge current would be 77.8 / 5 = 15.56 amps per battery. Or, for 3 batteries connected in parallel, around 45 amps.

I don’t see where they specifically mention the absorption charge voltage (unless this is what they mean by “cycle charge”). But it is normally 2.4V per cell for an AGM battery. This would be 14.4 V for your batteries.

So, the way a 3 stage charger normally works is:
(1) in the “bulk charge” stage, it supplies a constant current (typically near the maximum rated current) to the battery until the voltage of the battery reaches the absorption voltage.

In your case, this means you would feed 45 amps to your battery bank until its voltage reaches 14.4 volts.

(2) Once it is at 14.4 volts, you begin the “absorption stage” where you hold the voltage constant, and the current decreases until it reaches the float charge current.

(3) Once at the float charge current, you drop the voltage to the float voltage (13.65 V) to maintain your batteries.


Anyway, the take-away from all of this is that to achieve maximum life out of your batteries, it is probably worth the investment to either buy a 3 stage charge controller or build one yourself.


PS: I am considering trying to build one to back up my solar panels. I will be discussing this over in in my charcoal generator thread.


Thank you very much for this info Kyle. Most of it is Greek to me without taking some serious time to wrap my brain around it . Which I will when the night comes. I will definitely bring it to my solar installing buddy so he knows exactly what my needs are at this time when selecting or building a charge controller. I worked with him for a few years going back 12-15 years. I am hoping to work with him part time this summer to pay for a system and learn all I can. He has always been a great friend and an awesome guy to work and deal with. Again thank you very much for taking your time to bring me this useful information.