Is a variable power supply a useful tool for the enthusiast?

  • Thread starter Thread starter altruistica
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altruistica

altruistica

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Hi guys,

A bit of topic but I'm currently fixing my motorhome. I need to check the alternator regulator which I suspect is knackered as in this film:

https://www.youtube.com/watch?v=RD7ySDiNdwA


I figured I could rig up a variable power supply using 2 9v batteries piggy-backed together (with links between - to -, + to +) then coming from this battery to a variable resistor (volume pot) which would give me 0-18V DC. This is all theory by the way.....I'm not sure it would work as I've never done it.

Anyway that would give me the necessary 14.6 V with which to test the regulator.

I also thought though, as I now own a lot of vintage (25 years plus) equipment, that a proper variable power supply might be a handy thing to have in the studio. What do you think of this :

DC Bench Power Supply Switch Mode Adjustable 0-30V 0-5A CSI 3005SM | eBay

Would it be suitable for testing audio equipment?

Cheers
Al
 
I know i've needed one on more than one occasion, but typically its needed if you are needing to troubleshoot parts of gear and have those parts removed and isolated from the parent device. Example...was having trouble with the headphone amp in my Tascam BR-20T halftrack. Would have been handy to be able to remove the PCB and test it on the bench outside of the deck as ultimately the problem was the power supply in the deck.

But I've lived without one and get my hands pretty dirty on projects. I do have one waiting for me that a friend got for next to nothing and has repaired but I'm waiting until I have funds to buy it off of him along with some other goodies.
 
Thanks Sweetbeats....I might jump on one......if it comes in half as handy as the mig welder I bought last year then it will justify the purchase.

Al
 
If you connect the positives together and the negatives together, then they're in parallel. You will theoretically get 9V out with more current available than just a single battery. In practice you'll probably have one try to charge the other (because they cant start at exactly the same voltage), overshoot, then the other will try to charge the first, overshoot... They will probably heat up and eventually die. They might not explode. ;)

To get 18V, they need to be in series - with the negative of one connected to the positive of the other. You then use the two remaining terminals as the + and - going to whatever you're powering.
 
Thanks Ashcat.......you see, I know zip about electronics but I've always been eager to learn.

Having said that though, I'm just thinking about the way I was told to wire the four 12V car batteries I have on the motorhome. I was told to wire them in a 'star' method, with all the negatives coming to a junction box and all the positives coming to a different terminal on the junction box. To these terminals, the solar panel regulator and charging block (fed from the alternator) all meet. I was told this was a better way of keeping all the batteries topped up equally and never thought that one battery might try and charge another?

Al
 
altruistica said:
Thanks Ashcat.......you see, I know zip about electronics but I've always been eager to learn.

Having said that though, I'm just thinking about the way I was told to wire the four 12V car batteries I have on the motorhome. I was told to wire them in a 'star' method, with all the negatives coming to a junction box and all the positives coming to a different terminal on the junction box. To these terminals, the solar panel regulator and charging block (fed from the alternator) all meet. I was told this was a better way of keeping all the batteries topped up equally and never thought that one battery might try and charge another?

Al
Click to expand...

Oooer! Never connect car batteries in parallel. They never have the same internal resistance or charge status so as Ashcat said, there will be odd current flows.

As regards multiple batteries and "star" wiring? The potential for disaster is too high IMHO. Auto batts' can supply HUGE currents and you can burn out a loom, start a fire in a instant.

Best IMO to have either one really Big Mother of a 12 volt or two BM 6 volts in series and get the right strap kit to connect them, starting a cold diesel can take over 1000A.

It is true that a very high capacity battery could be beyond the capabilities of the alternator IF allowed to fully discharge. So don't LET IT! You can also use solar panels to keep a trickle charge going when parked up.

No doubt there are all sorts of kits about for aftermarket auto-electrics beef ups but unless you know exactly what you are doing, don't.

Dave.
 
Hey Dave,

The four batteries I have wired in parallel are all leisure batteries..topped up by a solar panel ...so barring one of them going faulty I'm not sure how they would be affected.

Here's a post where there seem to be many differences of opinion:

wiring leisure batteries in parallel - VW T4 Forum - VW T5 Forum

I have another battery solely for the vehicle that is isolated from the other four. I read numerous articles and testimonies........I suppose only time will tell me whether I called it rightly or wrongly.

Cheers
Al
 
The general advice in that link would seem to support the advice I gave and which I have always understood, that batteries of any type, primary or secondary, should not be paralleled. I have certainly never seen it done in vehicles. Lorries use 2x 6volts if 12V system and 2x12V if 24. Forklifts use multiple big mothers always in series.

I would suppose that for specialist applications, solar power say, they might use VERY well matched parallel packs all made at the same time and which will age at the same rate. I bet however such a pack will still have a shorter life than an equivalent high capacity series stack. Then for very serious power storage there might be some clever current sharing technology at work?

My main concern however was that it seemed someone with little or no electrical knowledge was contemplating hooking up an ad hoc array of batteries?

BTW. "leisure" batteries are not as tolerant of "dirty" charge current as the old "wet" lead acids. Check with the maker before you connect a bog standard Halfords charger!

Dave.
 
Car and marine batteries are made to be discharged and recharged over and over again, but something like an alkaline 9V isn't. I think that makes a bit of a difference. If you can stand the voltage drop, you could use "steering diodes" to avoid most of the issues with a parallel arrangement.

The OP was looking for 18V out of the thing, though, and it just plain doesn't work with 2 x 9V in parallel.
 
ashcat_lt said:
Car and marine batteries are made to be discharged and recharged over and over again, but something like an alkaline 9V isn't. I think that makes a bit of a difference. If you can stand the voltage drop, you could use "steering diodes" to avoid most of the issues with a parallel arrangement.

The OP was looking for 18V out of the thing, though, and it just plain doesn't work with 2 x 9V in parallel.
Click to expand...

Ah! NOT so clever "current sharing technology"!

Dave.
 
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