Sizing battery to operate DC motor

[buddy91082]

We have a 12v, 1HP, permanent magnet DC motor (that is all the data we have) that will be used as a winch. Assuming we cannot operate on AC power due to alternating current.

We have a 40AH 12v battery. Assuming 1HP = 1kVA, then current = 1000VA/12V = 83 amps.

So with a 40AH battery, i can run the motor for:

40AH/83amps = .48 hours or 28.9 minutes at full load - is that correct?

Thanks.
b

 

[waross]

It depends.
If the winch is not fully loaded the current will be less.
AH are tested/specified at a specified discharge rate. At high discharge rates the specified AH tend to be less than stated.

Assuming we cannot operate on AC power due to alternating current.

How about a transformer/rectifier combination?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[buddy91082]

Thanks Bill. We looked at the transformer/inverter combo. We have a limited budget and it's a temporary installation. We figured batteries and a charger were cheaper. Worse comes to worse, we power the winch from our truck.

 

[ScusaMe]

Buddy,

F Y I


Did a Google search on 1-HP 12vdc Perm. Mag. motors.

Three different ones; Dayton, Hallmark Industries, and Leeson Electric .... all are spec'd at 80 amperes.

Calculates to 214 watts of losses or just under 29% losses ... Oofta!

So, your approximation of 1-HP = 1-kVA .... is close .... but perhaps a tad high.


Don't forget to factor in Thermal Protection for motor.


Historically, I think that DC Winch Motors have been Series type.

 

[mikekilroy]

it depends on YOUR BATTERY TECHNOLOGY.

If Li-Ion battery, then, yes, ah is ah is ah and you can do the math and say 2x ah rating will result in 30 minutes use.

If some form of lead acid battery then NO: higher than about 1/10 C rating will result in FASTER discharge than C rating. Google 20 hour rate. see examples like:

http://gbindustrialbattery.com/Battery_Options/AH_Ratings.html

http://www.acterra.org/ev/files/batteries_1.html

I don't recall the guy who named this unlinearity, but it exists: if you pull significantly more current than the ah rating then the life goes down significantly for lead acid designs.

 

[blacksea]

You must thinking about current limitation with direct connecting to 12VDC power supply as well. But with using PWM power amplifier current consumption maybe lower than calculated above.

 

[iop995]

Check alternator power from truck. If you can start-up truck engine, can extend time of DC back-up. Motor current will be supplied from alternator and battery, thus extending battery time. If it's a 2-3kW alternator will work w/o time limit.