motor power requirements

[junksasa]

My motor draws 24VDC / 5A and runs off a lead acid battery. If I input 120VAC / 15A in a AC>DC power supply what does it out have to be to run the motor? I've been told an output of 24VDC / 5A is not enough.

 

[cowboybob]

My motor draws 24VDC / 5A and runs off a lead acid battery. If I input 120VAC / 15A in a AC>DC power supply what does it out have to be to run the motor? I've been told an output of 24VDC / 5A is not enough.

You would like an output somewhat more than the maximum load you intend the power power supply to carry.

For the sake of the example. I'd suggest a 24VDC/10A (240W) supply (giving you a 50% duty cycle with the motor you mention at maximum load).

This would also take into account the initial motor startup surge current.

The input side of the supply would, in this case, draw (ideally) 120VAC at 2 amps.

Inefficiencies, however, would bump up the input current necessary somewhat, so a 120VAC/3A to 24VDC/10A power supply would probably be closer to the values you might measure at full load.

 

[misterT]

My motor draws 24VDC / 5A and runs off a lead acid battery. If I input 120VAC / 15A in a AC>DC power supply what does it out have to be to run the motor? I've been told an output of 24VDC / 5A is not enough.

That depends completely on what you are driving with the motor. Torque is related to current intake and speed is related to voltage. When you are running at constant speed, you'll need current to provide enough torque to match the friction and other loads. You need high currents if you want to accelerate quickly or react to load changes quickly. You can overdrive the motor quite significantly for a short period of time.

Secondly, the rated current is probably the max. continuous current. This means that you can put 5A throug the motor without it overheating at open air. The stall-current, or startup-current is much higher. You can deal with startup-currents with a large capacitor if the mechanical load is light enough. If you have heavy mechanical load you'll need more power to get the motor turning.

Do you have any more specs about the motor? Even a datasheet maybe?

If you do not have specs, could you measure this: stall the motor so it can not turn. Put constant current through it and measure the voltage across the motor leads. Maybe 500mA through the motor is OK. Do not stall it with constant voltage.

 

[junksasa]

Is it true that the motor will only take the amps it needs to run? As an example - If motor runs noload at 5A and needs 20A at certain times due to load, then the power supply could be rated at say 50A and the motor would be fine.

 

[Nigel Goodwin]

Is it true that the motor will only take the amps it needs to run? As an example - If motor runs noload at 5A and needs 20A at certain times due to load, then the power supply could be rated at say 50A and the motor would be fine.

Yes - under what circumstances does the motor take 5A?, is that full load?, no load?, or stall conditions? - what is the motor actually doing?.

 

[junksasa]

No motor specs only the model number HRS-775S. I measured the noload current which was 5A. I will try to measure the the load on the motor and see what it is. Thanks.

 

[misterT]

I measured the noload current which was 5A. I will try to measure the the load on the motor and see what it is.

If the noload current is 5A, then you have no chance driving a load with a supply that is limited to 5A.

I found this page.. https://www.ec21.com/product-details/Electric-Scooter-Motor--1260055.html
Does that look like your motor?

On that page is a table with three different motors with the marking HRS-775S.. which one you think yours is? Maybe the last one with nominal voltage of 24V?
If those specs are correct for your motor, then 5A noload current is too much. Maybe your motor is 12V and you are over-driving it with 24V?

Anyway, look at the stall-currents. They go as high as 128A!

 

[Nigel Goodwin]

No motor specs only the model number HRS-775S. I measured the noload current which was 5A. I will try to measure the the load on the motor and see what it is. Thanks.

As misterT has already said, if the no load current is 5A, then you need a really HUGE PSU to feed it.

 

[dr pepper]

Your initial statement is a bit misleading, you say if you input 120v at 15a, if a supply drew that much and outputted 24v you'd get over 70 amps.

Maybe you could use a small battery charger with current limit and a lead acid battery to give you some push when needed, this would work well if the motor doesnt run for more than a few minutes.

 

[junksasa]

What type of AC>DC power supply should be used to drive a DC motor? I have seen switched and linear power supplies. Some are regulated and others non-regulated. I want to use this instead of the large car size battery the motor currently uses.

 

[Reloadron]

Depends on the motor and the power requirements of the motor. For example how large is the motor? I have run 12 VDC 10 Amp motors using old computer power supplies. Generally most motors are easily pleased.

Ron

 

[JimB]

Generally most motors are easily pleased.

But conversely, many power supplies are not pleased to be driving a motor!
The devil is in the detail.

JimB

 

[junksasa]

Depends on the motor and the power requirements of the motor. For example how large is the motor? I have run 12 VDC 10 Amp motors using old computer power supplies. Generally most motors are easily pleased.

Ron

24VDC, 5A nominal, 10A loaded

 

[Reloadron]

Read what Jim B mentions. Then I suggest you give this link a read. While 24 VDC @ 10 Amp is useful it does not mention the type of DC motor. Thus as Jim mentions the devil is in the details.

Ron

 

[Nigel Goodwin]

Identical threads merged - please read the existing replies - moderator

 

[junksasa]

Read what Jim B mentions. Then I suggest you give this link a read. While 24 VDC @ 10 Amp is useful it does not mention the type of DC motor. Thus as Jim mentions the devil is in the details.

Ron

It is a brushed motor. I didn't find Jim B quip very helpful or useful.