12v Supply / Engine starter?

[catlotion]

prompted by an earlier heater thread - I was reminded that I still have an old Webasto heater that needs fixing. I was wondering what's the best option for 12 volt supply in the workshop. I don't really want to buy a battery and often need to set up a little test rig for 12v stuff at home. Any ideas? Ideally something with an engine start facility too as I'm rebuilding an old Mopar V8 in the garage (but that's another story).

something like this perhaps?
http://www.amazon.co.uk/RCB320-Workshop-Battery-Charger-Starter/dp/B0012EI1G8

But would the charger provide a 12v supply with sufficient current to mimic a leisure battery? I know our C-Tek has a separate supply mode which would do but no engine start obviously...

 

[Trundlebug]

How about one of these

https://www.aldi.co.uk/en/specialbu...-detail-page/ps/p/jump-start-with-compressor/

Other suppliers are available

 

[catlotion]

ooo! that looks just the ticket. Compressor too! Bargain. Thanks.

 

[David2452]

A bench power supply with variable voltage is a really useful thing to have as you can confirm that the serviced kit works as it should, e.g. with the Webasto that it will start and run from say 10.5v to 16v.

 

[the_branflake]

I'm not sure quite how much power you need but an old PC power supply could do it. You can normally get 12, 5 and 3.3v from them also. I did this years ago and still find uses for it now.

Really need to read the post better doh! Forget that then

 

[nigelmercier]

I'm not sure quite how much power you need but an old PC power supply could do it...

This would be the best plan; starter systems are not built for long term use, and often output 16V or more.

http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/

 

[William_H]

Yes you should have a power supply to provide 12v or better still 13v for testing gear. You willl need to be able to provide 6 or 7 amps fopr the heater test.
I think realistically for an engine start a lead acid battery is the only viable option. An old car battery is best cheap bet. A power supply would have to be really big to be able to sustain 100s of amps and for a period of cranking.
A power supply consists of either a big transformer with recdtifier then a regulator either series pass transistor or switch mode type regulator. The output of a transformer and rectifier is inevitably very poor regulation so no load you might get 20 volts if it is capable of holding 12v at full load say 6 amps. The regulator will reduce the output voltage on light load but allow full power on heavy load but the regulator will be complex and waste a lot of power.
The other option for the power supply isn the switch mode type where the mains are rectified to about 340v DC. This is switched at hundreds of kilohertz in a small transformer then rectified to give DC. A feed back loop varies the mark space ratio of the switched power to regulate the output. This is like a computer power supply or even arc welders at the big end of the scale. More efficient more complex and cheaper to build new.
I would suggest that OP look around the junk to see what he has. A computer power supply should run the heater. He might have a large transformer that could be used with a rectifier or even an old battery charger which could have a regulator attached. But we are getting into the realm of the electronic boffins here.

Just to waffle on here a bit. I bought a WAECO small compressor fridge. being an elctronics boffin I thought that should be easy to build a power supply to run it on mains at home. It has a voltage sensor to switch from 12v supply to 24v supply. It also has a low voltage battery switch off. I found a transformer rectifier with enough power to provide 5 amps at 12v under compressor load (ie enough volts to not operate low battery switch off) would produce such a high voltage on low load when compressor is off as to make the fridge think it was running on a 24v battery that was low and so switched off the fridge. (about 20v). A series pass transsitor regulator would be quite big and dissipate a lot of heat. (a 7812 IC is a typical series pass regulator of this type but rated at 1 amp). I solved the problem by running the fridge on 24 volts so half the current. I fitted a reed switch to sense when current drain was high and this switched a relay to switch in a higher voltage winding on the transformer. This crude 2 option regulator is able to keep the voltage within reasonable tolerance to operate the fridge with low power supply heating.

I also have a home made 12v bench supplky that can give about 5 amps at a pinch with series pass regulator. It weighs about 4 kg being mostly a big old trnasformer. It is very useful with variable voltage from about 3 volts to 18volts. I guess just what OP wants for the heater. But certainly no good for engine start.
good luck olewill