golf caddy motor control

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AllVol

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Please take a look at my project to see if I am on the right track.

I propose building a replacement motor controller that will, for the time being, simply control the forward speed of the caddy. There is no need for reverse, and I intend to add remote stop-start capability later.

The motor, battery, transmission and chassis are in good condition. Only the contoller needs replacement.

Will the attached circuit serve my purpose? I am using a standard 12-volt lawnmower or automobile battery, although I am not sure what amperage I will draw. The unit must provide easy walking speed over somewhat hilly terrain, for a minimum distance of 7000 yards.

Any suggestions or advice will be greatly appreciated.
 

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Hi AllVol,

I would replace the IRF510 with a more modern fet.
The maximum drain current (5.6A) is too low and the
RDSon (0,54hm is far too high. The fet will run hot
like hell, select a more modern device to replace it.

on1aag.
 
on1aag said:
Hi AllVol,

I would replace the IRF510 with a more modern fet.
The maximum drain current (5.6A) is too low and the
RDSon (0,54hm is far too high. The fet will run hot
like hell, select a more modern device to replace it.

on1aag.
Click to expand...

Thanks, friend. Good suggestion. I'll look at some others. I just happened to have that one handy.
 
AllVol said:
Thanks, friend. Good suggestion. I'll look at some others. I just happened to have that one handy.
Click to expand...

Yes it's critical that you know the worst case amp draw from the battery under all cases, uphill, locked rotor, etc and size the Mosfet properly. You may consider paralleling Mosfets and also consider heatsink requirements. I would suggest some kind of fuse or circuit breaker or current limiter to protect the high power components and battery.

Lefty
 
on1aag said:
I would replace the IRF510 with a more modern fet.
Click to expand...

In another thread I found the IRLZ34 recommended. Would you concur?

The Rdson for the '34 is 1Mhm: , versus .54hm: for the 510. Could you explain why one meg is better than <1 in this case? I'm thinking you would want very little resistance when the mosfet is conducting. Am I backward?

Thank you, Lefty. Yes, I am just trying to get approval of the circuit, now. I will add fuse protection, heat sinks where necessary and even by-pass caps in the finished product.
 
Last edited:
Hi AllVol,

I don't know where you got those figures because the datasheet
says that the RDSon is 0,035 hm: , 35 mhm: , not 35 Mhm:.

https://www.electro-tech-online.com/custompdfs/2007/05/irlz34n.pdf

But I think you should select a device with a max drain current
of at least 50 amps and a max RDSon of 10 to 20 mhm:.
See to it that the max VGS is also greater than + or - 12 volts.
And VDS preferably greater than 60 volts.

on1aag.
 
you really should put a gate resistor down for that FET, otherwise at the very least you run the risk of setting up a peirce oscilator.

Likewise concider beefing up the gate-drive (ie don't just use the ouput of the 555), this will ensure the FET switch's fast enough and hard enough and thus reduce its losses
 
on1aag said:
the datasheet says that the RDSon is 0,035 hm: , 35 mhm: , not 35 Mhm:.
Click to expand...

Yep, you are right. These old eyes ain't what they usta be!!

Thanks, Styx. I'll see to that with a little more research.
 
I have to agree with Nigel. You need to look at the 4QD site and consider the power you will need at 12 V DC. A 1 KW motor, which is not very big, will draw almost 100 A and more, if the motor is stalled.

You seem headed in the direction of MOSFETS, which is fine, but you should consider putting several of them in parallel and on a heat sink.

Last, one of the very nice things about the QD site is his discussion of saftey, such as what happens when you are going downhill and how to deal with it electronically. That is, not all DC motors can brake. John
 
At those current draw rates it's probably worth using an inverter to drive a higher voltage motor at a lower current. The heat loss alone will make it more effcient even if the inverter ciruitry is lossy.
 
Sceadwian said:
it's probably worth using an inverter to drive a higher voltage motor at a lower current
Click to expand...

That's possibly so, Scead and thanks for your reply. The problem is that I already have all the other parts, just lacking a replacement controller.

One of the design criteria was something that could be knocked together quickly and cheaply, but would be suitable for a couple of rounds a week playing mule to my golf sticks.

As all of you have pointed out, there may be just a bit more to it than that. But I will continue, and I hope all of you and others will be willing to string along with me. I have spent considerable time today studying the 4D pages... a very insightful work. Thanks, Nigel.

Thanks to everyone for the help.
 

For what you want, it looks like the really poor example they give may be all you need?, 4D admit a great many were made and used.
 
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