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

mramos1 · 2nd January 2007, 10:29 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, 10:39 PM

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

mramos1 · 2nd January 2007, 11:21 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, 01:22 AM

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

**Nigel Goodwin** · 3rd January 2007, 09:19 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, 09:38 AM

You only need ONE DPDT relay.

mramos1 · 3rd January 2007, 12:01 PM

Quote:

Originally Posted by Cabwood

You only need ONE DPDT relay.

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

agent420 · 3rd January 2007, 12:52 PM

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, 06:19 PM

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

agent420 · 3rd January 2007, 06:51 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, 07:15 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, 10:44 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, 09:24 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, 11:30 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, 12:56 PM

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.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

2nd January 2007, 10:29 PM	#1
mramos1	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 11:59 AM.

2nd January 2007, 10:39 PM	#2
Nigel Goodwin	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, 11:21 PM	#3
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 - + - +

3rd January 2007, 01:22 AM	#4
Sceadwian	Sounds like a good usage for a basic h-bridge. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

3rd January 2007, 09:38 AM	#6
Cabwood	You only need ONE DPDT relay.

3rd January 2007, 06:19 PM	#9
mramos1	I did detail it in the 3rd post. Looks like relays will have to be it for now.

3rd January 2007, 07:15 PM	#11
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 do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.