RS Battery Charger info - UK Vintage Radio Repair and Restoration Discussion Forum

RobinBirch · 13th Oct 2013, 9:40 am

Dear All,
I have unearthed an RS lead acid battery charger that has been very useful in the past and that seems to have most of its basic functionality ok.

However, the "charged" point seems to be out of adjustment and it doesn't seem to want to switch off. Internally there are 3 pots that I presume set up the various levels but I have no details on it. Does anyone out there have a data sheet with some maintenance info? or recognise whose charger they have rebadged?

TIA

Robin

Herald1360 · 13th Oct 2013, 2:18 pm

Just a thought..... does it actually switch OFF or simply drop back the output volts to float level when it senses the charging current has dropped back as the battery approaches full charge?

Maybe it even uses the UC3906 control IC- in which case there's plenty of info still about.

RobinBirch · 13th Oct 2013, 3:01 pm

Good thought, I think that's exactly what it does but there is supposed to be a level sensor that switches the green charged light on when it happens. I know the function works in that if you turn the battery size down to the next one down it correctly picks up that it is "charged" but not on the 12v setting.

Robin

Herald1360 · 14th Oct 2013, 7:57 pm

Not a lot of help, but that RS part number seems to have referred to at least two different chargers! A rather more modern looking but still discontinued one pops up from Google.

So...... what's inside the box?

McMurdo · 14th Oct 2013, 8:55 pm

In many commercial lead acid chargers, the voltage threshold triggers a timer that holds the output high for so long (gas or equalising charge) before reducing to float. So the sequence is main charge>threshold>equalisation>time delay>float.
Or of course it's faulty

Herald1360 · 14th Oct 2013, 10:28 pm

The 3906 charger controller IC is a bit cleverer than that- after a trickle current startup on a deeply discharged battery, when the voltage climbs to a reasonable level it switches over to a bulk charge state with a current limit for battery / power supply protection. When the battery voltage reaches a preset level, the charger goes into voltage limited mode and the charging current falls away as full charge is reached. When the current falls below a preset level, the charger switches over into float mode (voltage limited at a a lower level suited for permanent maintenance of charge) and can be left like that as long as you like, or the battery can be taken off charge for use.

It sounds complicated but the whole thing is programmed with a few resistors and just needs a suitable regulator transistor added to deal with the actual charging current control.

If the RS box control circuit is not simple to fix, building a new controller using a 3906 is not very difficult.

KeithsTV · 14th Oct 2013, 10:53 pm

The 3906 is also temperature compensated as sealed lead acid cells have a temperature coefficient of -4mV/C per cell.

If you want to build a simple temperature compensated charger a regulator using a 2.7v zener will provide approximately the correct temperature coefficient.

Keith

RobinBirch · 15th Oct 2013, 12:00 pm

I'll get the lid off again this evening and try and see what the controller device is. The technology is mid 1990s. I like the idea of replacing the guts.

I'll let you all know what I find tonight.

Cheers

Robin

RobinBirch · 15th Oct 2013, 6:34 pm

Ok guys, I get the impression that this is a very basic charger. Its active element is an LM339N which is a quad voltage comparator device so I am guessing that it just charges and then potentially settles to a trickle charge when done but nothing more than that.

See photo

Robin

Herald1360 · 15th Oct 2013, 9:51 pm

Hmmm....

You can do quite a few tricks with 4 comparators! Even using one as an opamp in a control loop. There's not much more than that inside the UC3906.

Still, if there's not much in it, you can always try reverse engineering or simply checking each component and replacing any faulty/out of spec parts. It worked before, so if all bits are OK, it should work again.

Since it's relatively modern, maybe an electrolytic blitz would do the biz.

RobinBirch · 16th Oct 2013, 4:02 pm

Herald, think I agree with you. I'm going to end up recreating the circuit.

Robin

Alistair D · 16th Oct 2013, 4:06 pm

In times gone by the R.S. technical department could sometimes help out with schematics.

Al

AC/HL · 16th Oct 2013, 4:15 pm

Has anyone got an old RS disc, they had the datasheets on them.

RobinBirch · 17th Oct 2013, 12:59 pm

The last datasheet I saw, still available on the RS site as an obsolete deveice, is purely operating instructions :-( However, it does mention that it is possible with an old battery that the "on charge" light may not go out so perhaps all is not lost. I'll try this with a newish 12V battery ad see if it works.

Robin

13th Oct 2013, 9:40 am	#1
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	RS Battery Charger info Dear All, I have unearthed an RS lead acid battery charger that has been very useful in the past and that seems to have most of its basic functionality ok. However, the "charged" point seems to be out of adjustment and it doesn't seem to want to switch off. Internally there are 3 pots that I presume set up the various levels but I have no details on it. Does anyone out there have a data sheet with some maintenance info? or recognise whose charger they have rebadged? TIA Robin Attached Thumbnails

13th Oct 2013, 2:18 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: RS Battery Charger info Just a thought..... does it actually switch OFF or simply drop back the output volts to float level when it senses the charging current has dropped back as the battery approaches full charge? Maybe it even uses the UC3906 control IC- in which case there's plenty of info still about. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

13th Oct 2013, 3:01 pm	#3
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: RS Battery Charger info Good thought, I think that's exactly what it does but there is supposed to be a level sensor that switches the green charged light on when it happens. I know the function works in that if you turn the battery size down to the next one down it correctly picks up that it is "charged" but not on the 12v setting. Robin

14th Oct 2013, 7:57 pm	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: RS Battery Charger info Not a lot of help, but that RS part number seems to have referred to at least two different chargers! A rather more modern looking but still discontinued one pops up from Google. So...... what's inside the box? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

14th Oct 2013, 8:55 pm	#5
McMurdo Dekatron Join Date: Jun 2009 Location: Staffordshire Moorlands, UK. Posts: 5,274	Re: RS Battery Charger info In many commercial lead acid chargers, the voltage threshold triggers a timer that holds the output high for so long (gas or equalising charge) before reducing to float. So the sequence is main charge>threshold>equalisation>time delay>float. Or of course it's faulty __________________ Kevin

14th Oct 2013, 10:28 pm	#6
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: RS Battery Charger info The 3906 charger controller IC is a bit cleverer than that- after a trickle current startup on a deeply discharged battery, when the voltage climbs to a reasonable level it switches over to a bulk charge state with a current limit for battery / power supply protection. When the battery voltage reaches a preset level, the charger goes into voltage limited mode and the charging current falls away as full charge is reached. When the current falls below a preset level, the charger switches over into float mode (voltage limited at a a lower level suited for permanent maintenance of charge) and can be left like that as long as you like, or the battery can be taken off charge for use. It sounds complicated but the whole thing is programmed with a few resistors and just needs a suitable regulator transistor added to deal with the actual charging current control. If the RS box control circuit is not simple to fix, building a new controller using a 3906 is not very difficult. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

14th Oct 2013, 10:53 pm	#7
KeithsTV Nonode Join Date: Aug 2007 Location: South Bradford, West Yorkshire, UK. Posts: 2,573	Re: RS Battery Charger info The 3906 is also temperature compensated as sealed lead acid cells have a temperature coefficient of -4mV/C per cell. If you want to build a simple temperature compensated charger a regulator using a 2.7v zener will provide approximately the correct temperature coefficient. Keith

15th Oct 2013, 12:00 pm	#8
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: RS Battery Charger info I'll get the lid off again this evening and try and see what the controller device is. The technology is mid 1990s. I like the idea of replacing the guts. I'll let you all know what I find tonight. Cheers Robin

15th Oct 2013, 6:34 pm	#9
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: RS Battery Charger info Ok guys, I get the impression that this is a very basic charger. Its active element is an LM339N which is a quad voltage comparator device so I am guessing that it just charges and then potentially settles to a trickle charge when done but nothing more than that. See photo Robin Attached Thumbnails

15th Oct 2013, 9:51 pm	#10
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: RS Battery Charger info Hmmm.... You can do quite a few tricks with 4 comparators! Even using one as an opamp in a control loop. There's not much more than that inside the UC3906. Still, if there's not much in it, you can always try reverse engineering or simply checking each component and replacing any faulty/out of spec parts. It worked before, so if all bits are OK, it should work again. Since it's relatively modern, maybe an electrolytic blitz would do the biz. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

16th Oct 2013, 4:02 pm	#11
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: RS Battery Charger info Herald, think I agree with you. I'm going to end up recreating the circuit. Robin

16th Oct 2013, 4:06 pm	#12
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: RS Battery Charger info In times gone by the R.S. technical department could sometimes help out with schematics. Al __________________ I won't tell you how I discovered that.

16th Oct 2013, 4:15 pm	#13
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: RS Battery Charger info Has anyone got an old RS disc, they had the datasheets on them.

17th Oct 2013, 12:59 pm	#14
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: RS Battery Charger info The last datasheet I saw, still available on the RS site as an obsolete deveice, is purely operating instructions :-( However, it does mention that it is possible with an old battery that the "on charge" light may not go out so perhaps all is not lost. I'll try this with a newish 12V battery ad see if it works. Robin