How would you do this? / Control wiring question.

[iwire]

OK, a friend of mine and I are doing a small off hours project* and we had a wiring issue, my friend came up with way I would never have thought of. His plan worked as he expected but we have since change directions. I will fill in all the details later.

Here was the problem.

We have a control box that provides one, two wire 12VDC, 5 amp output that has three states

• No output
• 12VDC, positive on terminal 1 negative on terminal 2
• 12VDC, negative on terminal 1 positive on terminal 2

In other words the control box flips the polity of the terminals. This control box was designed to directly control a small DC motor in forward and reverse. However, we needed to control a 24 VDC, 40 amp motor with it.

He came up with a solution that only required one low cost trip to an auto-parts store, I will explain it later but wonder what other folks would come up with.


Thanks in advance.




(*Full disclosure, we are electricians doing work for ourselves in his garage, there may be adult beverages involved, any mention of the NEC or safety is strictly prohibited. )

 

[GoldDigger]

Just to get the assumption straight, was the available 24V DC supply to power the motor grounded or floating?
And you do need to be able to reverse that motor?

Tapatalk!

 

[don_resqcapt19]

I expect that he bought something like this.

 

[petersonra]

a 2pdt switch with form z contacts

 

[iwire]

I expect that he bought something like this.

Kind of, not so heavy duty and we used four of them.

a 2pdt switch with form z contacts

That sounds expensive. We spent under $5.00 at the auto parts store.

Does that have a open position in addition too two closed positions? We need forward, backward, stop conditions.

How would it interface with the two wire polarity swapping signal?

 

[iwire]

Just to get the assumption straight, was the available 24V DC supply to power the motor grounded or floating?

:thumbsup:

Floating.

And you do need to be able to reverse that motor?

Yes, video will be up soon but we needed forward, reverse and stop.

 

[iwire]

Here is what we are making.

It is an remote controlled electric trailer mover. The trailer and the lift weigh about 4500 lbs combined. The machine has to be able to push it off the street, over some bumps and into my buddies garage.

The video is last Saturday night, we are still making changes.

 

[K8MHZ]

Awesome project!

I saw a huge version of what you are doing made to move semi trailers into a construction site. IIRC, the controls were corded. I thought it was a great idea and haven't seen one since.

 

[PetrosA]

That will only get to be really fun when you drive it while standing in the lift.

 

[mjf]

Very nice.

 

[ActionDave]

I would do something to make the whole rig move faster and then get out of the garage and chase the neighbors cat.