Question about an H Bridge

[Ad8chd]

Hello and thank you in advance to anybody who helps me out. This is my first post hopefully it’s in the right place. I’m trying to build a little miniature winch mostly for fun just to see if I can, also if it works it would be cool to have something to drag logs up the hill with. I’m using a 24 V motor that was repurposed out of a hoverround mobility scooter. I’m using an on off on switch with a 12 V Li Ion battery pack to trigger 4 automotive relays (2 at each position) that will send 24 V from 2 deep cycle batteries to the motor. I’m under the assumption that I will have to deal with some back EMF from the motor when I change directions, I’m also under the assumption that that can be dealt with with flyback diodes. When I go to Google, I can find schematics that are what I’m doing, but there’s flyback diodes on all the coils of the relays but nothing around the motor. If it was only going One Direction, I know it would go across the motor terminals, but with a bi-directional setup I’m pretty sure that that cannot be a thing. I’m a doofus, and I already had one little fire and blew up a big diode, I’m gonna blame that on ChatGPT. Also, I’ll blame it on me, OK it’s my fault. I did it, if anybody could shine a little bit of light on this for me, I would greatly appreciate it. Thank you again.

 

[Nigel Goodwin]

Just diodes on the relays should be fine, and if you're just using mechanical switches?, no diodes at all would probably be fine as well - the diodes are there to protect the driver transistors, which can be destroyed by the voltage spike.

 

[crutschow]

If you want to suppress any back-emf from the motors (which may not be needed for the relay contacts but couldn't hurt) requires four diodes, two on each motor lead.
One diode goes from the motor lead to the V+ (cathode to V+) and one from the motor lead to common (anode to common)

 

[Ad8chd]

Just diodes on the relays should be fine, and if you're just using mechanical switches?, no diodes at all would probably be fine as well - the diodes are there to protect the driver transistors, which can be destroyed by the voltage spike.

That’s awesome, thank you. I almost used mosfets but I found the relays and figured it would be easier and a bit more robust.

 

[Ad8chd]

If you want to suppress any back-emf from the motors (which may not be needed for the relay contacts but couldn't hurt) requires four diodes, two on each motor lead.
One diode goes from the motor lead to the V+ (cathode to V+) and one from the motor lead to common (anode to common)

Thanks for the response, I probably should have mentioned in the post (because I already got tripped up on this) that these are automotive relays so they don’t have a common pin. I’m gonna give it a shot like Mr Goodwin suggested and just go Wild West footloose and diode free… I’ll keep you guys posted on my bumblings, and try to get a video if there’s any more fireworks lol

 

[Diver300]

If you use

Thanks for the response, I probably should have mentioned in the post (because I already got tripped up on this) that these are automotive relays so they don’t have a common pin. I’m gonna give it a shot like Mr Goodwin suggested and just go Wild West footloose and diode free… I’ll keep you guys posted on my bumblings, and try to get a video if there’s any more fireworks lol

By "common", Crutschow meant the negative of the supply.

 

[Ad8chd]

If you use

By "common", Crutschow meant the negative of the supply.

Oh, duh… lol it might be hard to tell from my calm, confident, demeanor, But as far as the electronics goes, I am not what one would call an expert… I’ve been trying to learn some stuff because it’s interesting to me, but it’s almost like they’re trying to keep this stuff a secret, all this damn math and vocabulary words. Who would’ve thought electrical engineering would be so complicated?

 

[Diver300]

There are automotive relays that have a normally open connection and a normally closed one. The terminals are often marked 30, 87 and 87A. If you used those, you only need two relays. Wire +ve to 87 on both relays, and -ve to 87A on both relays. Connect the motor between the terminal 30 on one relay and the terminal 30 on the other relay.

 

[Diver300]

Oh, duh… lol it might be hard to tell from my calm, confident, demeanor, But as far as the electronics goes, I am not what one would call an expert… I’ve been trying to learn some stuff because it’s interesting to me, but it’s almost like they’re trying to keep this stuff a secret, all this damn math and vocabulary words. Who would’ve thought electrical engineering would be so complicated?

It's the same for all disciplines. People who are familiar with the language don't always realise how obscure it can be to others.

In particular, in electronics, circuit diagrams are all-important but many people who don't use them don't even understand how much information can be in them, or how much can be understood from a brief glance at one.