Driving max current hi and low from a battery - Electronic Circuits Projects Diagrams Free

mramos1 · 2nd January 2007, 09:29 PM

I have a unit that I need to drop a battery across two terminals. After 5 seconds I need to flip the battery backwards between the terminals. If I do it by hand it works but I want to let a PIC do the work.

I was going to use relays, then I thought maybe FETs might do it. I did see an EDN article with 2 transistors that would drive the ground side to milivolts. Or something like a 1/2 an H-bridge. Did did try with NPN/PNP and just get not get what I wanted. If it can be done with transistors that is fine too.

I have a pic chip running in 3 volts (2xAA so close) and want to drive this lite load back and forth to 0 and +3V. But I want as much of the battery there as I can get to the terminals.

I was thinking a pair of FETs on each of the two connections. Does anyone have an input on this.

Thanks.

EDIT: continued in third post...

**Nigel Goodwin** · 2nd January 2007, 09:38 PM

Looks like an obvious job for a DPDT relay - nice and simple, and minimum voltage loss.

mramos1 · 2nd January 2007, 10:21 PM

I have one G6HU relay. Now if I had 3 more it would be done

Sorry Nigel, I mentioned only 1/2 the project since I was hoping for a solidstate version and would dup it and drive them with the pic. Relays I will need 4 DPDT.. I can see if RadioShack still sells them.

The project is actually 2 sets of the terminals and they work together.

Code:

   T1-1   T1-2    T2-1    T2-2
1   +        -         +         -
2   -        +         +         -
3   +        -         -         +
4   -        +         -         +

Sceadwian · 3rd January 2007, 12:21 AM

Sounds like a good usage for a basic h-bridge.

**Nigel Goodwin** · 3rd January 2007, 08:19 AM

Quote:

Originally Posted by Sceadwian

Sounds like a good usage for a basic h-bridge.

But more complicated, and more voltage loss!.

Cabwood · 3rd January 2007, 08:37 AM

You only need ONE DPDT relay.

mramos1 · 3rd January 2007, 11:00 AM

Quote:

Originally Posted by Cabwood

You only need ONE DPDT relay.

Think you missed post three, or I missed something..

agent420 · 3rd January 2007, 11:51 AM

Quote:

Originally Posted by mramos1

I have a unit that I need to drop a battery across two terminals. After 5 seconds I need to flip the battery backwards between the terminals. If I do it by hand it works but I want to let a PIC do the work.

I'm just curious what this means; what is the application? Perhaps there are other solutions if we knew what the problem was?

mramos1 · 3rd January 2007, 05:19 PM

I did detail it in the 3rd post. Looks like relays will have to be it for now.

agent420 · 3rd January 2007, 05:51 PM

I must be higher than usual, because I don't see anything below that gives a clue what you are attempting to do, or what the 'unit' is...

Quote:

Originally Posted by mramos1

I have one G6HU relay. Now if I had 3 more it would be done

Sorry Nigel, I mentioned only 1/2 the project since I was hoping for a solidstate version and would dup it and drive them with the pic. Relays I will need 4 DPDT.. I can see if RadioShack still sells them.

The project is actually 2 sets of the terminals and they work together.

Code:

   T1-1   T1-2    T2-1    T2-2
1   +        -         +         -
2   -        +         +         -
3   +        -         -         +
4   -        +         -         +

Hero999 · 3rd January 2007, 06:14 PM

I'm confused to, I assume that you just want to swap the terminals round.

You don't need a PIC with your relay, a single 555 timer will be cheaper and more effective as the 200mA output can drive the relay without using a buffer transistor.

mramos1 · 3rd January 2007, 09:43 PM

Quote:

Originally Posted by Hero999

I'm confused to, I assume that you just want to swap the terminals round.

You don't need a PIC with your relay, a single 555 timer will be cheaper and more effective as the 200mA output can drive the relay without using a buffer transistor.

I need to change the times on it and not sure on the times yet and some cycles might be longer than others. So 555 is out, I will just use transistors and drive some relays, but was hoping to use just transistors like an H-bridge.

For the table below, T1-1 is terminal 1 pin 1, T1-2 is terminal 1 pin 2, T2-1 is terminal 2 pin one, T2-2 is terminal 2 pin 2. +/- is the battery position I want connected to them.

Code:

   T1-1       T1-2        T2-1        T2-2
1   +            -             +             -                 for 5-20 seconds
2   -            +             +             -                 for 5-20 seconds
3   +            -             -             +                 for 5-20 seconds
4   -            +             -             +                 for 5-20 seconds

I am just looking for a good driver to force the + and minus, all the rest works and is done.

I think Nigel said just use a relay.. That might be the only way. I did make a NPN/PNP driver but there was a lot of loss pushing the minus side.

**Nigel Goodwin** · 4th January 2007, 08:24 AM

Quote:

Originally Posted by mramos1

I think Nigel said just use a relay.. That might be the only way. I did make a NPN/PNP driver but there was a lot of loss pushing the minus side.

An H-bridge is only trying to imitate a relay - and not doing a very good of it. Relays are cheap, simple, reliable, and perform better than an H-bridge. The only advantage of an H-bridge is if you want to use PWM power control - and even then you can do it single ended, and use a relay for reversing.

agent420 · 4th January 2007, 10:30 AM

Quote:

Originally Posted by mramos1

I need to change the times on it and not sure on the times yet and some cycles might be longer than others. So 555 is out, I will just use transistors and drive some relays, but was hoping to use just transistors like an H-bridge.

For the table below, T1-1 is terminal 1 pin 1, T1-2 is terminal 1 pin 2, T2-1 is terminal 2 pin one, T2-2 is terminal 2 pin 2. +/- is the battery position I want connected to them.

Is there some reason you do not wish to communicate what it is your doing? I get you are trying to switch polarities around, but on what and for what purpose? It's a lite load, but you need as much battery as possible?

Mostly, I'm just curious. But also sometimes other people can provide insight on a project solutions you may have overlooked.

mramos1 · 4th January 2007, 11:55 AM

Quote:

Originally Posted by Nigel Goodwin

An H-bridge is only trying to imitate a relay - and not doing a very good of it. Relays are cheap, simple, reliable, and perform better than an H-bridge. The only advantage of an H-bridge is if you want to use PWM power control - and even then you can do it single ended, and use a relay for reversing.

Unfortunatly I think it will involved PWM later. It is an electroplating process, for not the relays will do to get it started.

Can a transistor H bridge really get it down to 0volts without tons of extra parts? FET will switch faster, but I do not believe it is required. But the 3904/3906 version did not go to 0 well. Late for work, but will post what I tried later tonight.

Thanks for all the help.

2nd January 2007, 09:29 PM	(permalink)
mramos1 Experienced Member	Driving max current hi and low from a battery I have a unit that I need to drop a battery across two terminals. After 5 seconds I need to flip the battery backwards between the terminals. If I do it by hand it works but I want to let a PIC do the work. I was going to use relays, then I thought maybe FETs might do it. I did see an EDN article with 2 transistors that would drive the ground side to milivolts. Or something like a 1/2 an H-bridge. Did did try with NPN/PNP and just get not get what I wanted. If it can be done with transistors that is fine too. I have a pic chip running in 3 volts (2xAA so close) and want to drive this lite load back and forth to 0 and +3V. But I want as much of the battery there as I can get to the terminals. I was thinking a pair of FETs on each of the two connections. Does anyone have an input on this. Thanks. EDIT: continued in third post... Last edited by mramos1; 3rd January 2007 at 10:59 AM.

2nd January 2007, 09:38 PM	(permalink)
Nigel Goodwin Super Moderator	Looks like an obvious job for a DPDT relay - nice and simple, and minimum voltage loss. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

2nd January 2007, 10:21 PM	(permalink)
mramos1 Experienced Member	I have one G6HU relay. Now if I had 3 more it would be done Sorry Nigel, I mentioned only 1/2 the project since I was hoping for a solidstate version and would dup it and drive them with the pic. Relays I will need 4 DPDT.. I can see if RadioShack still sells them. The project is actually 2 sets of the terminals and they work together. Code: T1-1 T1-2 T2-1 T2-2 1 + - + - 2 - + + - 3 + - - + 4 - + - +

3rd January 2007, 12:21 AM	(permalink)
Sceadwian Experienced Member Blog Entries: 1	Sounds like a good usage for a basic h-bridge. __________________ Curiosity killed the cat; That's why they have nine lives.

3rd January 2007, 06:14 PM	(permalink)
Hero999 Experienced Member	I'm confused to, I assume that you just want to swap the terminals round. You don't need a PIC with your relay, a single 555 timer will be cheaper and more effective as the 200mA output can drive the relay without using a buffer transistor. __________________ What's so bad about Microsoft? Get Opera it's simply a superb browser.

3rd January 2007, 08:37 AM	(permalink)
Cabwood Experienced Member	You only need ONE DPDT relay.

3rd January 2007, 05:19 PM	(permalink)
mramos1 Experienced Member	I did detail it in the 3rd post. Looks like relays will have to be it for now.

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