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wrxer 13th October 2012 10:39 AM

portable testing power supply
1 Attachment(s)
I work away from home and to while the long hours away, I have brought a couple of faulty amps with me to try and fix. This is difficult without a 12v power supply for testing.
I bought a 14.8v lipo r/c battery and wired in a fuse and current limiting light. I dont think the 14.8v will upset any amps as they should receive 14.4v anyway.
Attachment 306173

Could be handy for when out and about buying amps at swap meets or garage sales etc.
I am using a DSO scope too, maybe not for the purists, but it does me fine for a first scope. If I need to upgrade it, and i use it enough, i will.
Cheers Jack

AKHeathen 13th October 2012 10:22 PM

be careful not to exceed the safe output of that battery. to rapid of a drain and they like to go "boom" most amps should idle 2-4a, which might be a tad high, but their turn-on current is much greater

blazer40 13th October 2012 10:47 PM

How do you like the little scope?

TechStaff@SonicCraft 14th October 2012 01:42 AM

Speaking of power supplies, is there a preferred 12v source unit? I've been eyeing the Samlex SEC-1235M, but it's only 35A. I don't know that I really -need- more than that, but I'd like to know what's available and make an informed choice.

I've been repairing and modding for a while now, but it's usually 120v units. The Samlex seems like awfully good bang-for-the-buck.

AKHeathen 14th October 2012 02:52 AM

what's the price? all i know of are pyramid, which is a solid semi-budget line, little 2-10a supplies, and my home-made ones.. i don't see any reason a 35 cannot support repairing and operating a 10k without problem, unless you are going for major power testing/clamping, which can be done in-car, like i do. to make things easier on myself, i'm going to build a 200a+ supply in my workbench, but that's a long-term project.

TechStaff@SonicCraft 14th October 2012 03:02 AM

They're pretty widely available for 135-150. Amazon, I think, had them for about that.

Perry Babin 14th October 2012 05:45 AM

The PS-52KX is the best bang for the buck right now (as far as I know). $144 on eBay with free shipping. I prefer Astron supplies but they're more expensive.

wrxer 14th October 2012 10:20 AM

Yeow, the PS-52KX are $400 delivered to Australia..But they look nice.

The power supply on the bench at home is similar to this:
12V 33A 400W DC Regulated Switching Power Supply CNC 400W Hi Quality | eBay

I'm not sure what you guys think of its details, I have put it in a enclosure, added a 50A shunt and analogue meter, (will add a matching V meter soon). It is adjustable on the output, so I wound it as high as it would go. It peaked out at about 13.5v from memory.
I am thinking of getting another bigger one to replace or complement the one I have now.

I have a car battery I could beef up the supply with, but I dont know how to connect it in or if it needs protection from the power supply.

As for the DSO, This is my first scope and I wouldnt know how it compares. But it will tell me when a amp is clipping, lets me look at square waves on the rectifiers and signal waves in the preamp and output stages. It is portable and has pretty good battery life. I love it, but I dont know any better.

The lipo battery is a 45c, it is only 2Ah but advertised to deliver 80 odd amps and 100 amps peak. Even if this is mostly advertising it should be OK for me. The current limiter is 55w, so it will choke the supply down to around 5A anyway

Cheers Jack

Perry Babin 14th October 2012 01:23 PM

I didn't look at ebay in Australia. It's hard to believe that it's not available there. It seems that someone would be selling them in Australia but I couldn't find any for sale there.

The battery will have to be fused, just as it would in a vehicle. The rating of the fuse would depend on the size of the wire used to connect it to your test bench.

If you're using something like a car battery, you should have a way to quickly disconnect it in case there is a problem. This is especially important if you're using large gauge wire and a large fuse.

You will need to make sure that it's in a well ventilated area as well, especially if it's being charged after being significantly discharged.

You would also have to fuse the amp (for amps without on-board fuses) if the fuse used in the wiring for the battery was significantly larger than what's suitable for the amp.

You need to protect the terminals of the car battery so that nothing can fall across them.

I'd suggest fusing the supply wiring as well, inserting a fuse between the point where the supply wiring connects to the battery wiring. This will protect the smaller wire from the supply in case the supply fails catastrophically or in case something falls across the terminals of the battery.

wrxer 15th October 2012 09:48 AM

All of that makes sense, but I was thinking more of would there need to be some diodes or something to stop the power supply trying to dump 30A of current into a battery when it is partly flat and you disconnect or turn off the amp?

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