treadmill permanent magnet DC motor as generator

[almac]

picked up a treadmill from the kerb, connected a multimeter to the motor and walking on the treadmill produces more than 60Vdc very easily. in the amp setting i could feel the load and had no trouble getting 10 amps with moderate effort. just wondering if i rigged it up to an old lawnmower what charge controller would i need to use as a 24v battery charger? i will post some pics or a video of the treadmill producing current 2mor

[Mike90250]

You rock dude ! 10A @ 60v is 600W you are a super mega athlete.

[almac]

not sure what the Vdc was in the amp reading. the 10 amp i maintained for a few seconds didnt want to fry my cheap multimeter. the specs of the DC motor are 3400rpm 220Vdc 6.5 Amps. so its a 1400W motor? would the voltage output of the motor be constant with a given RPM? when i produced 10 Amps the RPM felt like about the RPM i had at about 10-20Vdc

[Sunking]

Very few people in the world can generate that much power (.8 HP) and only for a few seconds. Most folks are more like 1/4 Hp or 200 watts.

[almac]

Very few people in the world can generate that much power (.8 HP) and only for a few seconds. Most folks are more like 1/4 Hp or 200 watts.

thanks for the info, so that means the voltage during the amp test was around 15v. so back to my idea, the motor is a 2HP motor. 1500W ?? so running off a pulley from a 2 stroke lawn mower, can i use an ordinary PWM charge controller? would the voltage output vary with the load from the batteries?

[almac]

ok i will have a go at this, the lawnmower and 2HP DC motor were both free of the kerb, so i will hook up this motor to the lawnmower and aim for a pulley ratio /RPM to deliver a voltage to comply with a yet to be determined solar charge controller. to charge my 24v battery on successive cloudy winters days

[inetdog]

ok i will have a go at this, the lawnmower and 2HP DC motor were both free of the kerb, so i will hook up this motor to the lawnmower and aim for a pulley ratio /RPM to deliver a voltage to comply with a yet to be determined solar charge controller. to charge my 24v battery on successive cloudy winters days

Since you will have an essentially uncontrolled voltage, and a relatively stiff source which might be damaged by overcurrent I would recommend that you get an MPPT type CC.
Your ratio should be determined to produce a voltage of at least 32V, preferably 36, while at full load on the motor/generator. You will probably have to do some more extensive testing with controlled RPM and varying resistance loads to figure out what that RPM point will be.

You could also set there watching a voltmeter and ammeter and varying the throttle during the entire battery charge and maybe do without the CC. If you do that, be sure to put a high current diode or diode group between the motor and the battery bank.

[almac]

Since you will have an essentially uncontrolled voltage, and a relatively stiff source which might be damaged by overcurrent I would recommend that you get an MPPT type CC.
Your ratio should be determined to produce a voltage of at least 32V, preferably 36, while at full load on the motor/generator. You will probably have to do some more extensive testing with controlled RPM and varying resistance loads to figure out what that RPM point will be.

You could also set there watching a voltmeter and ammeter and varying the throttle during the entire battery charge and maybe do without the CC. If you do that, be sure to put a high current diode or diode group between the motor and the battery bank.

thanks , will go with a mppt they start at about $100 for one that can take up to 100Vdc. would risk wrecking a PWM or the batteries with the diode method.

[Sunking]

thanks , will go with a mppt they start at about $100 for one that can take up to 100Vdc..

Sure about that? Way to cheap for MPPT. A real 15 amp MPPT controllers start at $200 and go up from there. Sounds like you are looking at Chi-Com knock-off frauds.

[sensij]

I'm not so sure that either an MPPT or PWM controller is a great choice. The mppt will believe it has control over the source, and attempts to find the maximum power point may vary the effective load in ways that lead to instability. In other words, the IV curve of the motor will not look like the IV curve of a solar panel, so the result may be unpredictable. Also, some mppt controllers switch to a PWM mode once bulk charging is complete, which would also be incompatible with this design.

A PWM controller is definitely not a good idea, since it can potentially open up the circuit between the generator and the load.

I think the best approach would be a shunt type controller with a fixed dump load. It should be able to run somewhat autonomously, and when the battery voltage hits the desired level the power from the generator can be shunted away until someone intervenes to shut it off (or fuel runs out). Blocking diodes or other reverse current protection are important. Commercially, many wind turbine charge controllers are designed this way, googling diversion controller or dump load controller also gives lots of hits. For those with some electrical skill, DIY designs are out there too.

[almac]

I'm not so sure that either an MPPT or PWM controller is a great choice. The mppt will believe it has control over the source, and attempts to find the maximum power point may vary the effective load in ways that lead to instability. In other words, the IV curve of the motor will not look like the IV curve of a solar panel, so the result may be unpredictable. Also, some mppt controllers switch to a PWM mode once bulk charging is complete, which would also be incompatible with this design.

A PWM controller is definitely not a good idea, since it can potentially open up the circuit between the generator and the load.

I think the best approach would be a shunt type controller with a fixed dump load. It should be able to run somewhat autonomously, and when the battery voltage hits the desired level the power from the generator can be shunted away until someone intervenes to shut it off (or fuel runs out). Blocking diodes or other reverse current protection are important. Commercially, many wind turbine charge controllers are designed this way, googling diversion controller or dump load controller also gives lots of hits. For those with some electrical skill, DIY designs are out there too.

thanks, at 1st i was thinking of wind turbine controllers due to the variable voltage but most are rectifiers for 3 phase ac generators. where would i find a dc wind turbine charge controller? also a quick search found this item about why solar charge controllers dont work for wind turbines / generators.

also found this useful piece about RPM and voltage calculations with permanent magnet dc motors.

Ametek and treadmill motors.
The best DC (Permanent Magnet)motor for use as a generator is the one that has the highest rated voltage at the lowest RPM figure (this applies to Ametek and treadmill motors).
There is some useful information on different Ametek motors which can be found at "tlgwindpower.com/ametek.htm". As treadmill motors are supplied by a multitude of vendors there is no one source of similar information.
You should be able to calculate the number of RPM required to generate one volt. This figure is useful for comparing DC generators. Simply divide the stated RPM on the rating plate by the voltage on the rating plate. DC motors are linear devices, voltage and speed form a straight line graph. Lets assume that one volt is produced for every 20RPM. As the controller requires about 17v to fully charge a 12v battery (see Introduction above) then the DC motor will have to turn at (17 x 20) = 340RPM. This is frequently called the "cut in speed" which is the lowest speed at which the generator will charge the battery. At speeds above 340RPM the quantity of current generated and delivered to the battery will increase. DC generators require a "blocking diode" to prevent the controller/battery from powering the generator as a motor.
You stand a much better chance of charging a 12v battery than a 24v one as the "cut in speed" is half for 12v compared with 24v systems.

http://www.ebay.com.au/gds/Wind-Turb...6308446/g.html

http://www.windbluepower.com/articles.asp?ID=127

[jflorey2]

thanks, at 1st i was thinking of wind turbine controllers due to the variable voltage but most are rectifiers for 3 phase ac generators. where would i find a dc wind turbine charge controller?

You don't use charge controllers with generators; you match the base speed to the generator RPM range and then choose your throttle setting to deliver the power you want.

[almac]

You don't use charge controllers with generators; you match the base speed to the generator RPM range and then choose your throttle setting to deliver the power you want.

ah thanks jflorey2, having just found the info about dc motor RPM and voltage that make good sense , but i can see another problem that might still require a charge controller. as the battery charges and the current falls the load on my victa lawn mower will also fall causing the RPM and voltage to increase then destroying my batteries in a smokey hot battery scenario , been there done that

[jflorey2]

as the battery charges and the current falls the load on my victa lawn mower will also fall causing the RPM and voltage to increase then destroying my batteries in a smokey hot battery scenario , been there done that

That's why you throttle back as load drops. All "simple" (i.e. non-inverter) generators use a throttle feedback mechanism to maintain frequency and voltage. Inverter-based generators do as well - it's just a bit more complicated since you no longer need to support a given frequency, and are thus free to throttle back significantly when load is low.

[sdold]

Serious question: why not use a reel mower? It seems to do exactly what you want, i.e. the mower gets its power from strenuous walking.