Quick and dirty PSU

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gninnam
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Quick and dirty PSU

Post by gninnam » Sat Feb 02, 2019 1:01 pm

Hi All

So, having got the Lenco working well in its new plinth felt it missed a perspex cover.
Ordered a large sheet of perspex and decided to build a plexiglass bending machine.
All good and used an old laptop PSU (19v) but not generating enough grunt to get the Nichrome to glow.

Lashed up a PSU using some old parts dotted around which puts out around 32v DC.
All good.

I use one of those cheap programmable control supply power modules from China (0 to 50v, 0 to 5A) which works well with the laptop PSU.
When using my lashed up PSU it is showing 32v with no load, when I hit the button to send power to the cables connected to the Nichrome the control unit powers down then powers up and keeps doing this.

Will a power regulator sort this out or something else (not sure I have a power regulator of sufficient power in my box of bits)?
Can get pics if required to help with the rambling above :)
Cheers

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ed
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Re: Quick and dirty PSU

Post by ed » Sat Feb 02, 2019 2:01 pm

I'm not conversant with the application you're messing with here but I've made a fair few power supplies for hot wire cutters with nichrome in the past....they can be trixy...

In danger of egg-sucking lecture here, but have you seen this:

https://jacobs-online.biz/nichrome_wire.htm

should give an indication of current requirement, depending on the length and gauge you're using.
There's nowhere you can be that isn't where you're meant to be

gninnam
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Re: Quick and dirty PSU

Post by gninnam » Sun Feb 03, 2019 1:27 am

Thanks Ed - very informative.

I used the gauge of Nichrome based on a forum post of someone who did the same thing (think he used a 22 gauge while min is 24).

Anywho - a few pics of the bendy unit I built plus the lashed up PSU - hopefully help you understand what is what!
If I can get the PSU working fine then I will put it together properly and also in a box.

Image

Image


This post shows that I have set the max output to 25V and 5amp, the input is around 33v.
As soon as I switch it to output it resets the unit:

Image

Cheers

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ed
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Re: Quick and dirty PSU

Post by ed » Sun Feb 03, 2019 9:04 am

I can't really see what's going on in the photos but I'm guessing your wire length is not much more than 1 foot.....
If that is correct then the maths doesn't seem to add up.....

24 gauge will give you about 1R5 per foot which I calc to be about 20 amps if you're using 32 volts. If you look at that supply conservatively and give it the benefit of the doubt then you might be looking at 20-25v under load then you might still want 14 amps.

for the work I've done in the past, which admittedly is not quite the same as you're doing here..I've used 40" bows with 18 gauge wire and minimum of 10amp tx, bridge with heavy duty mosfet regs....the meter hovers around 4-5 amps for cutting white foam normally. Bearing in mind I don't want to shred the foam I only get to cutting temperature, it's unlikely such a rig would get the nichrome red without complaining.

I'm guessing, but there may be a thermal cut-out in your supply which is triggering.

if it were me I'd beef up the supply, lengthen the wire(or think about a resistor) and stick an ammeter in circuit.
There's nowhere you can be that isn't where you're meant to be

gninnam
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Re: Quick and dirty PSU

Post by gninnam » Sun Feb 03, 2019 8:56 pm

The length of the nichrome is around 29 inches so over 2 feet.
The power supply module only goes up to 5 amp so not enough grunt.
I connected one of the laptop PSU's direct to the nichrome - 19.5v and 11 amp output.
Still not enough
I have 2 identical PSU's (from Dell laptops) with 19.5v and 11 amp output - could I pair these together someway to increase the volts and amps?
Or could I just connect my lashed up PSU direct to the nichrome (not put the meter on for the amps but would have thought a few will be made?

Cheers

gninnam
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Re: Quick and dirty PSU

Post by gninnam » Fri Feb 08, 2019 7:56 pm

Put 2 PSU's in parallel to boost the amps and all good - the nichrome now glows red:

Image

And it works - bent a test piece perfectly :)

Image

Image

Used 2 identical PSU's (out, 19v and 11 amp). In parallel got 19v and 21 amp

little eddy
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Re: Quick and dirty PSU

Post by little eddy » Fri Feb 08, 2019 8:21 pm

Ingenious. Will be nice to see the finished product.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.

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Mike H
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Re: Quick and dirty PSU

Post by Mike H » Sat Feb 09, 2019 5:04 pm

Test piece, good, full width?

Image

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gninnam
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Re: Quick and dirty PSU

Post by gninnam » Sat Feb 09, 2019 6:46 pm

Yep - and here is the result.
Discovered I need a new jigsaw as mine doesn't keep the blade straight so will have another go once I buy another one but this is a good start.

Image

Image

Image

CHeers

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IslandPink
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Re: Quick and dirty PSU

Post by IslandPink » Sat Feb 09, 2019 7:00 pm

Wow - that's a bit shoddy !
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Dave the bass
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Re: Quick and dirty PSU

Post by Dave the bass » Sat Feb 09, 2019 8:53 pm

Conservatory's for TT's, who'd have thought it!
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gninnam
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Re: Quick and dirty PSU

Post by gninnam » Sat Feb 09, 2019 9:10 pm

I was thinking more a terrarium ;)

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ed
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Re: Quick and dirty PSU

Post by ed » Sat Feb 09, 2019 9:25 pm

well done for the bending, looks well precise.
I did wonder about the safety though vis sliding the lid slightly backwards without any sides on. If it slips off the back then won't it demolish the arm?
There's nowhere you can be that isn't where you're meant to be

gninnam
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Re: Quick and dirty PSU

Post by gninnam » Sat Feb 09, 2019 10:32 pm

The plan is to put sides on then I will look to have something on the back for mounting to the plinth (not hinges though)
Hopefully all will come obvious soon!

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Mike H
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Re: Quick and dirty PSU

Post by Mike H » Sun Feb 10, 2019 2:17 pm

Well, that's a .. Image
 
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