Anyone Put A 10-Turn On A Megawatt.

[MEXICOWANDERER]

A ten turn potentiometer?

With poor eyesight and a crippled hand I sure could use some disassembly and reassemble tips. Such as what needs to be done to gain access under the board to solder leads for the pots? I have two Megas to do. Particularly interested in steps that require dexterity with 2 hands.

Thank You Kindly!

[MEXICOWANDERER]

No.
Amparo, is changing the 18-CREE flood lamp over the work table for me today. My internet access cannot be from home unless it is done by smart phone and I was awaiting news that my extensive package from HSC, HALTED ELECTRONICS had been configured correctly and is on it's way from Santa Clara, CA. They have a basic website with catalog BTW. So I spend the day at Mercado del Sur connected to their modem. For the last seven years they tell me, Phone Internet Service has been unavailable here. The connect to a modem kind.

I have a 2nd Megawatt waiting for me in Chula Vista. Plus a lot of electronic components for the Mega and for line spike suppression. Gas Discharge tube, avalanche TVS diodes,a pound or so of 20mm MOVS, and lots of PICO 2-amp fuses.

What I REALLY need at this point is a pair of 6" long RACK HANDLES, to protect the rooster-beak-knob switch and two ten-turn pots that go atop the BORG. Ten inch rack handles are not out of the question. Even industrial-looking stainless drawer handles would work. My fear is to smack the BORG and have something vital get smashed. The housing is something like 20 gauge steel sprayed with Krylon bed-liner.

[NinerBikes]

MX, did you attempt a soldering exercise yesterday on your MegaWatt?

[MEXICOWANDERER]

A hundred kudos for your image. Putting in another 100-watts of LED lighting over the work table today to assist my almost eyesight.

[CapnCampn]

Looks like I just soldered to the back 2 legs, left the front one alone. Had to remove the top cover to access, but didn't have any trouble with the soldering iron - there's only one resistor nearby.

Here's a thousand words or so.

[landyacht318]

Yes, two of the legs on the mini pot are in the same trace on the circuit board. The third is just for tripod status.

This was the same on both Cheapowatt and Meanwell rsp-500-15.

Nipping off the mini pot's legs at the pot cleanly would be easier than desoldering, making sure the holes are clear, then soldering in 22awg wires to reach a remote 10 turn pot.

I do not know if this could be managed without opening the unit for access. I didn't try, but taking things apart started happening for me at age 3.

[MEXICOWANDERER]

Are they using the third leg solely for structural support? A tap plus one of the other two remaining legs would be enough, right?. Knowing which two of the three legs sticking up are live is the challenge for my eyes and coordination. Geeze I hate getting old. I've got the talent but my body betrays me. Hibernation for 20-years in the power-supply technology learning department don't help either. I remember a battery manufacturer shouting to me (Arif Sinan owner of Keystone Batteries) "You have got to see this solid state charger (A Todd 75-amp) light as a feather, and a really good price." Problem was frequency intolerance - the first time a generator went offline and spun down it blew up that power supply. I lost interest.

But I digress. As soon as the images arrive I will save them to disk. Then using hemostats, A Third Hand, the Octopus and various Mueller clips I am going to try and solder that Tefzel wire to the correct terminals. If I need to add a wee resistor, I'll do it on the pot end.

Yeah I did see the legs (2) sticking up. Daymare: Touch a soldering iron to a snipped leg and boink it drops down out of sight. When I do not know something I ask for help. I am all eyes and ears, here.

[JiminDenver]

Mex

This is probably a stupid comment but I am looking at the pot on my Mega with 3.25 readers and a 20x glass. All I see going from the pot to the board are three legs. Why couldn't you just snip the legs and solder to them?

[CapnCampn]

I'll try to remember to take a picture tonight.

LY is correct- More resistance = lower voltage, so even if you don't goop the original pot, you can only accidentally turn the voltage down.

CC

[MEXICOWANDERER]

I did consider paralleling but I am super cautious down here due to the 1,500 mile long trip to get a new one. I'll do "the parallel" then GOOP the single turn pot. That rear terminal on the Mega's pot is a bear to get to.

Thanks for the tips.

[landyacht318]

I have done the cheapowatt, and the Meanwell, but not a Megawatt. The pics somebody posted of the Mega's internals did not make it look significantly different than the cheapowatt. The components looked burlier but the circuit board did not appear to have more traces or more tightly packed traces. The cheapowatt appeared to be a copy of the megawatt, just using the least expensive components they could.

My Meanwell is a double sided circuit board and more closely clustered traces.

The Cheapowatt thread has some good pics in it of the Megawatt provided by Mena661:

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27939135/srt/pa/pging/1/page/9.cfm

BOth cheapowatt and meanwell used 1K ohm potentiometers. I know you said you bought 500 Ohm 10 turn pots. I'm not sure these will have the voltage range you desire. IIRC the 0 ohms was maximum voltage and 100 ohms minimum voltage, so a 500 ohm unit will likely increase the minimum voltage well outside of float range, if that is a factor.

That is of course if it has a 1K ohm pot.

I know the Pot on my Meanwell when removed read 973 ohms, and before I swapped it out minimum voltage was 13.23v. The 10 turn 1k Ohm pot I got maxed out at 1017 ohms, and when installed then minimum voltage fell to 13.12v when unloaded, I've seen 13.06v under a light load.
Max voltage with either Pot was 19.23v unloaded. I never loaded it at max voltage.



The Meanwell was more difficult to disassemble, and significantly harder to desolder and resolder some wires to it, but I've gotten a heck of a lot better at soldering since I did the Meanwell last October.

The Thermal pads between transistors/ and heatsink might tear on removal.

The thermal grease applied in the factory is nasty stuff, seemingly impossible to clean once it gets on fingers or other surfaces.
Actually accessing the circuit board is quite simple, just removing the phillips screws from the casing's lid, pulling the connector for the cheesy sleeve bearing fan, and then those Phillips screws which go through the bars which hold the transistors tight to the casing or heatsinks on the sides.

If you have the Megawatts with you next time you are on this side of the border, I'd gladly do it for you. I am about 40miles north of Chula Juana. I can give you some of those 18650 cells I just harvested from my older laptop battery pack. Not sure of their remaining capacity yet, but I really only need about 6 to 8 of them in my rotation, and I now have close to 18 of them left. But the panasonic ncr18650B's are not in the equation. I paid ~12$ a piece for those and their greater capacity is easily noticed in my uses.

[MEXICOWANDERER]

BORROWED COMPUTER down at the store during the day then one-fingered tapping on the Galaxy after 5PM. I'm worse at voice recognition now. Microwave banda is jammed at night so I do the best I can.

[CapnCampn]

I did. But I didn't feel like disassembling the whole durn thing, so I paralleled the 10 turn with the original pot - just soldered my extensions to the appropriate pot legs on top of the board. It increased the voltage available by ~.5v - about right for what I wanted.

CC

I mentioned it here:

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28279273/gotomsg/28281131.cfm#28281131

"On my recently acquired MegaWatt 400, I didn't feel like pulling the whole thing apart to replace the pot. So I just paralleled the new 10 turn with the original and set the original to as low (resistance) as it would go (Highest voltage). To do this I just soldered zip wire to the exposed legs of the pot on top of the board, and ran it to the new pot, stuck to the top of the PS with mounting tape.

On these supplies, lower resistance corresponds to higher voltage - noted by Landyacht & confirmed on mine. Parallelling the pots allowed me to shift the resistance down just a smidge, since the original pot had a range of ~1-980 ohm or so. Now I have <1 to ?something just under 980?. The voltage available was ~9.5 -15.5V, now it's about 10-15.8 . Numbers are approximate, I did this a month or so ago. "

[NinerBikes]

You're getting pretty good at dictating to that little smart phone to post, aren't ya, MXwanderer?

[MEXICOWANDERER]

The single pot original pot has to be removed, the entire Megawatt disassembled, in order to access the circuit board under the single turn pot. Then extension wires (25 ga (?) ) need to be soldered in to run to the new 10-turn pot.

Can I do this with 1-1/4 working hands? It would help immensely to read someone else's account, hopefully detailed that would allow me to conjure up a vision whether or not I would have the ability do this myself or go on a 440 mile overnighter journey and let a communications radio tech do the work.

The Megawatt is a power supply. It built differently than a CheapO and it is built differently than a Meanwell.

Most people have full use of both hands. I do not