Hughes MCW-550 microwelder - looking for service manual / fuses values / schematic

manual available for rent :

This one (which maybe you already found) has a little bit about operation and calibrating the weld voltage.

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Interestingly, it also claims that this device originally had NiCd batteries, instead of Pb. (It does mention a "dry lead acid battery" option for serial no. 2200 and up, which might be the Cyclon Pb batteries you have.)

That business seems to buy and sell equipment like that; maybe they would sell you a copy or scan of the manual.

It looks like it should provide a square wave, at the specified voltage and duration, to the main output. When the main output is not on, it should charge the batteries, to get ready for the next output.

It also looks like there are "sense" wires coming back from the weld head to the "Voltage Fire" connector, to help the power supply maintain the correct voltage at the weld electrodes. (4-wire measurement or Kelvin connection). The scan above shouts very loudly that you should not operate this device without those "sense" wires hooked up.

Matt Roberds

• This site seems to be more or less a duplicate of
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  . The "warehouse tour" video shows the same building.

Exactly that's the "part" of manual that i got. As You can see it's not full because scanned pages are 2,3 and 4. On page 4 there is say "see page 16" so maybe at end there was some kind of schematic or block diagram.

That's how battery looks like:

I never saw this before, it's single cell.

12 of them was stacked in parallel and series to get 6V 20Ah.

I replace them using four 4.5Ah 6V SLA Gel battery like this

?p=6V+4.5aH&fr=&fr2=piv-web&hspart=ddc&hsimp=yhs-linuxmint&type=__alt__ddc_linuxmint_com

Im pretty sure they have lower "short circuit" current than Cyclon but anyway in short period they should work just for test to give me indication how it's welding.

You have right, tt try to charge battery, i can see voltage putted on battery clamp but it's kind low like 6.x volts. That's not enough to charge 6V cell... it should be at last 7.2v.

I also found notice on battery "do not adjust charge voltage without batteries connected" but still i can't find potentiometer for that adjustment :)

That square wave and timing i should be able to test using oscilloscope but right now it's look like this:

When i hook up without head i can see around 6V on analog voltage indicator - we can assume that's battery voltage.

When i plug weld head - voltage on meter drop to 0.

That's question why is that happening, i do not press fire.

That's quite odd behavior... maybe there's short inside weld head... im going to test it but i have to open it (weld head) and do some measurement.

Website:

I can't access it... and manual for rent also look not good for me. I'm from europe so borrowing paper copy it will be difficult.

Better option for me will be donate by paypal someone who have paper copy, to take pictures of it and share with me.

I'm going try write karenmadison.com maybe they have full copy of manual.

I first saw a battery like this in a mid-1980s rechargeable flashlight, but I don't see them very often. They are made in several sizes, from

2.5 Ah to 25 Ah. The Pb plates are wrapped in a spiral @, not in parallel || like most batteries.

I think they used to be more popular before switching power supplies got popular; sometimes the power supply design was easier if you could have multiples of 2 V, rather than 1.2 V (NiCd), 1.5 V (C-Zn, alkaline), or

6 or 12 V (Pb-acid).

Originally Cyclon cells were made by Gates, which mostly made rubber products (water hoses and drive belts for cars, trucks, etc). In the early 2000s they were made by Hawker, and are now labeled Enersys. One of the factories is about 50 miles (70 km) away from me.

In the US, you can get car starting batteries made like this, with six of these cells in series. Johnson Controls' "Optima" brand was the original, but other companies make similar products now.

Enersys' selection guide

says that these cells have an internal resistance of 3.5 milliohm and short circuit current of 570 A when fully charged. The battery of 12 cells would have had an internal resistance of approximately 2.6 milliohm (plus the resistance of the connecting wires), and a short circuit current of about 2280 A (!!).

If you get good ones (like

), the internal resistance for each battery will be 40 to 45 milliohms, or 10 to 11.3 milliohms for four in parallel. The manufacturer doesn't specify a short circuit current, but does give a 10 second discharge current of 45 A. 180 A for four in parallel.

Even if this welder was originally built for a NiCd pack, which probably used 5 x 1.2 V cells, 6.x wouldn't be enough charging voltage. (It would be for 4 x 1.2 V cells, though.)

It looks like there are a couple of small "sense" wires that go back into the control plug, in addition to the two heavy "main" wires that go to the weld head. There might be some high value resistors (100k ohm?) from the "main" connector to the "sense" connectors inside the welder, to keep the power supply somewhat regulated when there is no weld head plugged in. With the weld head plugged in, though, perhaps the supply requires the "sense" wires to be there, and one of them might be open or shorted.

Good idea.

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Were the lead-acid cells really connected in series? The output voltage (from that manual) was up to 1.99V, or 1.30V into 2 milliohms, so 650 Amps, which comes from the battery according to the manual. In that case, the type of battery may be very important, as some batteries would have much more internal resistance than the weld, and would prevent the desired current from being achieved.

Perhaps it would be interesting to try replacing the lead-acid cells with supercapacitors. You can buy a 3000 Farad 2.7V supercapacitor rated for 1900 Amps and actually capable of quite a bit more, for about $65 from Digi-key. You would have to figure out whether the output voltage regulating circuit of your welder can run from a 2.7V capacitor, or whether it would need several capacitors in series due to the regulator having too much drop-out voltage. You would also need a voltage balancing circuit for the capacitor charger - which could probably be built with a TL431 plus power transistor for each capacitor in the series string.

I have been thinking of building a spot welder from supercaps, but I am unsure how much voltage I will need. I think about 10 in parallel, for

19000A, should be enough to weld about anything I would want to, but whether I need to stack them in series as well is the question. To switch the current off after the weld, (and perhaps also regulate the current, with a switched mode current source - if I can make suitable inductors...) it seems like multiple 100A rated MOSFETs are about the optimum amps per dollar. Getting low enough on-resistance is not the limiting factor, as a much larger number of mosfets will be needed to get the current rating high enough.

Chris