Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Hughes MCW-550 microwelder - looking for service manual / fusesvalues / schematic

On 21/09/2014 04:03, wrote:
Hello,

I'm try to fix very old Hughes MCW-550 microwelder that i rescued from being dumped and give it a second life for my use.

To fix it im in big need of service manual, schematic or any detailed manual (i found in Google some pdf-s but they have just technical details like advertisement) nothing about proper operation, calibration and testing if device is working properly.

Here is video that i shoot of this unit at my workbench:
https://www.youtube.com/watch?v=6dBmXFVgaxQ

I just finished fixing fuses holder and other small things that were smashed but still need right fuses values.

It's in creepy condition, some diodes are corroded so i will have to replace them anyway, i'm also going to poke every semiconductor and test it but right now im in point that i don't know how it should operate while it's 100% working. Without service manual or operator or schematic to help me understand what's going on it will tough to examine.


Right now i'm working on replace original dead 6V Sealed-Lead Cyclon acid battery using standard (4x in parallel )4.5Ah 6V gel battery.

If someone could share any experience it will be great.

Regards



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

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