Help with 12v system.....

Louwai (Bryan) · #1 13-01-2010, 12:02 AM

A couple of yrs ago I built a 12v / 240v power box for the scope. I put it in a DIY thread at the time, searched but can't find the thread.

It was an empty PC tower fitted with a 240v to 12v transformer as well as a 12v to 240 inverter. Has a 12v inlet & a 240v inlet with switches to isolate each when the other is being used.

Anyway, it's been working fine every time I use it. Last time I used it, it had a little hic-cup with 12v supply cables, but was quickly fixed.

Tonight I set up in the back yard, plugged in the 12v supply & blew a fuse. Started checking the general circuits with a meter.

Direct short between + & -.
I disconnected cables checking with the meter as I go. Everything is connected correctly. I can't for the life of me figure out how or why I'm registering a circuit between pos & Neg.

Anyone got any ideas???

tlgerdes (Trevor) · #2 13-01-2010, 09:34 AM

Look at screws holding equipment to case. Could be some circuit board has moved and is now grounded.

Gama · #3 13-01-2010, 10:42 AM

It may have a diode protection input. Possibly damaged/blown and now shorting across the input.

Theo.

erick (Eric) · #4 13-01-2010, 02:18 PM

Disconnect that 12v-->240 volt inverter and check the rest of the wiring?

Louwai (Bryan) · #5 13-01-2010, 06:15 PM

Quote:

Originally Posted by erick

Disconnect that 12v-->240 volt inverter and check the rest of the wiring?

I'll do that Eric.

I did put the meter across the + & - of the inverter 12v inlet terminals & it registered a circuit. But i don't know the internal workings of an inverter so I don't know if that's correct.
I just assume that it's not.

I'm going to build a new distribution box anyway, but this is what I need to use until then.

B

Bassnut (Fred) · #6 13-01-2010, 07:03 PM

"12v inlet terminals & it registered a circuit", what, a short circuit?. If not, the 240-12v supply might have a shorted bridge rectifier (square black block with 4 legs, or, 4 seperate power diodes with 2 legs each) see if the +- legs on the bridge, or any of the diodes show a short, easy and cheap to replace. If the invertor has a shorted input, that could be painfull. As Eric says seperate the 2 and test seperately.

erick (Eric) · #7 13-01-2010, 08:18 PM

Quote:

Originally Posted by Louwai

I'll do that Eric.

I did put the meter across the + & - of the inverter 12v inlet terminals & it registered a circuit. But i don't know the internal workings of an inverter so I don't know if that's correct.
I just assume that it's not.

I'm going to build a new distribution box anyway, but this is what I need to use until then.

B

"...registered a circuit..." You would expect some resistance. I suggested you disconnect the inverter since all the rest of your circuitry is just switches, wires and sockets? You should be able to find a fault in that lot easily.

I'm fairly sure that just putting a resistance meter across the 12V input to your black box of tricks isn't the right approach.

Louwai (Bryan) · #8 13-01-2010, 09:20 PM

Well I put it all back together exactly the way it was. Still with the same "readings" on my little meter.
Hooked up the 12v batteries & away it went.

240v globe works from the inverter & the 6x 12v outlet sockets all work fine.

So. Really.... What was I complaining about?????

mithrandir (Andrew) · #9 13-01-2010, 09:28 PM

Quote:

Originally Posted by Louwai

Well I put it all back together exactly the way it was. Still with the same "readings" on my little meter.
Hooked up the 12v batteries & away it went.

240v globe works from the inverter & the 6x 12v outlet sockets all work fine.

So. Really.... What was I complaining about?????

Loose strand of wire somewhere that shorted the rails?

Cable pinched somewhere and insulation worn through?

Disassembling and reassembling might have cleared the problem, but you should recheck all the cables and connections.

erick (Eric) · #10 13-01-2010, 11:03 PM

Perhaps a sad little fuse that decided it was time to go Phut?

Louwai (Bryan) · #11 14-01-2010, 08:14 AM

Quote:

Originally Posted by erick

Perhaps a sad little fuse that decided it was time to go Phut?

Who knows!!!!!!

It's all working fine,
BUT my meter still shows that i have a connection between the + & -.......

I need to build a new one anyway. I suppose I'll just need to do it sooner rather than later.........

Next one will be a plastic chassis & case.......

erick (Eric) · #12 14-01-2010, 10:19 AM

Quote:

Originally Posted by Louwai

BUT my meter still shows that i have a connection between the + & -.......

I think you are just seeing internal circuitry of your inverter - I presume that is still connected.

Louwai (Bryan) · #13 17-01-2010, 09:27 PM

We'll here's my beast.
This board will be permenantly fitted into my astro trailer along with the 2 batteries & I will also carry 4 solar panels for re-charging.

I've added a 240v inlet so I can charge with a 240v battery charger.

The board has 2 12v power outlets + 1 12v inlet to plug the solar panels into.
3 light switches (will have 3 lights in the trailer)
Pleny of room for more.

It works.
Have tested it with Solar Panels & also the 240v charger.
Run all the gear for a few nights in succession.

Everything is fab........

mswhin63 (Malcolm) · #14 18-01-2010, 12:58 AM

Nice beast. Travellers pack.