Advice needed for powering universal motor 4

DAta21117 · Jun 30, 2021

The equipment has a brushed motor running on fully rectified and unfiltered 120 VAC. The motor is rated at 13 Amperes. There is no nameplate. I do not know the RPM.
The goal is to either operate the motor on batteries or replace the motor with one which will run on 24 VDC (two 12 volt batteries) at the lowest possible cost. I really don't want to spend $400 on an inverter and waste all that power in the conversion.
I know that I could measure the RPM and find a motor, but I suspect that the cost would be considerable.

TugboatEng · Jun 30, 2021

To run that motor at 24 volts you're going to be pushing a minimum of 65 amps in to it. What low cost batteries do you think are going to support this?

waross · Jun 30, 2021

It will probably run well on about 90 Volts DC.
Back in the day, trailer mounted, engine driven welding sets typically had a 90 Volt DC receptacle to run heavy duty 120 Volt AC angle grinders. Some of those grinders would be in the 13 Amp range.
at 24 Volts it may run too slow to be useful.
By the way, both Tug and I are giving you WAGs (Wild Ass Guesses) because you don't include enough information for a proper answer.
If you tell us what the equipment is, it will save a lot of time and someone may have direct experience with your device.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

DAta21117 · Jun 30, 2021

Had I taken a moment to realize the amount of power used by the motor I would have been able to avoid the question.
Thank you Bill and Tugboateng.
The application is a remote controlled electric mower.
Starting with a 120 VAC corded mower. Adding a 24VDC wheelchair. Trying to eliminate the power cord for the mower. It takes an hour to mow the lawn with the mower by hand. The mower not only cuts the grass, it sucks grass up and mulches it as well so there is a lot of air being pushed around. The mower has a simple full bridge diode between the switch and the motor leads.
I don't think that there is an inexpensive solution, except to leave the mower corded and make an umbilical cord for the chair control. Hopefully, interference will not become a problem.

If this turns out to work reasonably well, I will post instructions on

https://www.instructables.com/

so that others who want to mow their own lawns in the heat and humidity can join me. (The last time I mowed it took far too many sessions to complete.)

Thanks again!

jraef · Jun 30, 2021

I think it is too much energy needed to run a 1560W motor for an hour continuously on a self-propelled mower. You would need 65 A-h of battery power just for that mower blade motor, not counting the chair, controls and guidance system (assuming you get a DC-DC booster to take the 24VDC up to what the motor needs). But for a mower, as the voltage drops you will lose blade speed and cut less, taking even MORE energy to muscle through the grass. So you really should start out with at least twice that much because you don't want to exceed a 50% DoD (Depth of Discharge). Let's then start with 130 A-h of battery power. Then if using the same batteries for the wheelchair drive and supporting systems (servos etc. todo the guidance control), means adding EVEN MORE. Assuming 50Ah 12V AGM motorcycle battery will weigh about 30lbs and taking a SWAG at 150 A-h, that would be 6 of these batteries, meaning the mower setup must be able to carry around at least 180 lbs of batteries with it to do the job. The power / weight issue starts to get out of control quickly.

But good luck, let us know how it comes out.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

3DDave · Jun 30, 2021

I think most mowers have excess power to make up for the user not keeping the blade sharp. I notice that a very sharp blade cuts (!) the lugging of the engine on my gas powered motor. Being willing to sharpen the blade more often might be enough to cut the power required by 20-50%. However, the blade dynamics may require a similar velocity at impact to actually cut the grass.

Anecdotally, a sharp blade is also key to finding errant rocks which a dull blade will never hit.

BrianE22 · Jun 30, 2021

Don't they sell cordless lawnmowers?

jraef · Jun 30, 2021

BrianE22, yes, but they are typically not self propelled for the reasons I outlined above; it takes too much power. In this case (as I interpreted it) he wants to adapt an existing corded electric mower to make it cordless and make it not only self propelled, but also remotely guided. Those are made too, but they have limitations, usually they can do less than an acre of lawn in one charge. Plus they are VERY expensive as mowers go. I looked at one from Husqvarna, I think it was around $2500 US, not including the cost of installing the perimeter wire (limit line). I still considered it though, mainly to see if I could hack it to chase the ground squirrels that are tearing up my yard...

https://www.youtube.com/watch?v=q2bP7j7kLBI

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

edison123 · Jun 30, 2021

"hack it to chase the ground squirrels that are tearing up my yard."

That's just nuts.

Muthu

http://www.edison.co.in

3DDave · Jun 30, 2021

Buy a Rat Terrier or similar.

itsmoked · Jun 30, 2021

Sickle bar mowers are noted for the small amount of energy they require. They are the lowest powered mowers. They have no windage and they don't cut each blade of grass five or six times. If you want to cut a lot of acreage with a small amount of energy check them out.

Keith Cress
kcress -

http://www.flaminsystems.com

waross · Jul 1, 2021

Here's another option. No batteries needed.

Perimeter barrier system:
No need for expensive and time consuming burial.
Easily moved.

Easy recall of grass cutters after use.

Edit: I forgot to mention the free fertilizer as an added benefit.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

jraef · Jul 1, 2021

3DDave said:
Buy a Rat Terrier or similar.

If only. My wife is anti-dog because she doesn’t want to care for it and she knows I will eventually forget (which is true). Our new neighbors next door have a miniature Australian Shepherd, cutest thing in the world, they have no ground squirrels. I am thinking of cutting a hole in our fence so she can patrol our yard too.

In the mean time, my wife is “emulating” a dog by spraying ammonia around the yard every day, it seems to be having an effect. Way more work than caring for a dog if you ask me, but I know better than to bring it up…

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

DAta21117 · Jul 1, 2021

You guys(?) are cracking me up. Thanks for the suggestions, and the smiles too.
I don't understand forgetting to care for a dog though. Mine used to bring me his bowl when it was time.

3DDave · Jul 1, 2021

They make dog-talk buttons. It may take a bit of training at first, but apparently dogs get the idea of how to use them fairly fast. Getting them to push the "hungry" button when they are hungry seems like an easy start, along with "out" and "walk".

I'd make a deal with the neighbor - working dogs enjoy being useful. I've read of owners taking herding dogs to playgrounds and soon realizing that all the 3-5 year olds are in a tight group, not a nip or bark required, just getting in the way when a child is going away from the desired group.

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Advice needed for powering universal motor 4

DAta21117

Industrial

TugboatEng

Marine/Ocean

waross

Electrical

DAta21117

Industrial

jraef

Electrical

3DDave

Aerospace

BrianE22

Specifier/Regulator

jraef

Electrical

edison123

Electrical

3DDave

Aerospace

itsmoked

Electrical

waross

Electrical

jraef

Electrical

DAta21117

Industrial

3DDave

Aerospace

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