Modifying The 36-Amp Megawatt List Of Materials

[MEXICOWANDERER]

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• Cheap digital multimeter for ohms and volts. No calculations necessary. EZ job
• If you have some of this stuff, great, if not here are the links
• The silver heat sink grease is for replacing the zinc oxide on the Megawatt transistors and rectifiers -EZ to do. Yes, this grease transfers heat that much better
• The lock on the voltage adjustment potentiometer is to lock it so it doesn't move and the number help to pre-set it
• You'll also need a decent quality #1 and #2 phillips screwdriver
• A handy magnet to keep all the screws together
• Some rags to wipe off the white zinc oxide grease
• I need No.4 reading glasses. You may need stronger, weaker or none
• The "3rd Hand" alligator clip holder is worth it's weight in headache tablets to hold wires still when soldering
• The existing potentiometer does NOT have to be removed
• Only two small wires needed to be soldered to the Megawatt board
• The other end of the wires will be soldered to the potentiometer
• Geeky language will not be used, and no assumption will be made that you have ever soldered anything. No Einstein calculations
• This will be a step-by-step photo do-it-yourself complete with handy "why can't I?" answers

[johnm1]

I've been looking at installing a Boondocker BPCM-75 75 Amp Adjustable Power Converter/Charger, which by it's name has adjustable voltage and a volt meter. I also have a couple of DVM's. But, it's rated for 75 amps and by the title of this thread, the Megawatt is "only" 36 amps. Aside from the obvious math of 39 amps, what's different? Will it charge 2, or 4, 6v gf batteries the same speed?

My goal is to charge the battery bank using the genset for as short of a time as reasonably possible. I don't mind learning how to babysit and I don't leave the current genset running while not there so ... not much difference.

[MEXICOWANDERER]

The main difference is this...

(It takes human intelligence to operate the Megawatt, correctly). To settle this issue I will offer to bet a hundred dollars versus fifty dollars that I can recharge a depleted RV battery fifty to 100% TWICE AS FAST as any automatic charger. But it does take a bit of involvement. Like arising from a chair and check a battery cell to see if it is bubbling.

Batteries are PREDICTABLE. If it takes 2.2 hours to recharge from 12.08 volts static one time it will take 2.2 hours the next. I recommend a wind-up Intermatic Timer.

But for short-duration weekenders and umbilical connected specials, the semi automatic charger would be the best choice.

A five-hundred amp charger is useless if it decided to switch to float when the battery is 80% charged.

If there is a FULLY programmable charger out there, then it would beat the snot out of the Megawatt. The 25 year old Trace 2500SB modified sinewave inverter/charger was fully programmable and had all the bells and whistles.

[NinerBikes]

johnm1 wrote:
What's the difference between this modified Megawatt vs something like the Boondocker BPCM-75 75 Amp Adjustable Power Converter/Charger?

It's probably not for the "set it and forget it" type of camper.

[johnm1]

What's the difference between this modified Megawatt vs something like the Boondocker BPCM-75 75 Amp Adjustable Power Converter/Charger?

[MEXICOWANDERER]

I wish I had genuine internet 😞

[Byrogie]

How's the project going MrWizard?

[Byrogie]

No problem, MrWizard
I learned a long time ago:
Do not put pressure on volunteers, or you may end up with none.....

[MrWizard]

The Dakar is on me
I have the text and the pictures
I'm just slow as cold molasses when it comes to editing and putting together documents

Sorry for the delay, put yes it is a work in progress

[MiPaJacks]

Hi Piano,
Since Mex has left the building did he take his "Mex charger project" with him?
Is he active on some other site?
Is the charger project dead?
Is this something we are not supposed to talk about?
Thanks
James

[pianotuna]

MiPaJacks,

Mex has left RV.net. He is alive and well.

[MiPaJacks]

I'm sorry if everyone knows but me, but is this project still in process or has it decided to not undertake it?
and along that same line of thought, I haven't seen any comments from Mex lately. Is he ok? I love to read his postings.
James

[2112]

x

[MEXICOWANDERER]

I call converters that utterly fail to recharge a battery boondocking a "Zsa Zsa Gabor Backpacker". Some converters are better than others. But an hour at max output is sort of ridiculous for a top 20% charger. That would be 36 amp hours and still nowhere near full charge. If the power and cables check good. Yank the scrap and hurl it at a howling dog. Putting in a divider switch to halve 12 volts could allow a second power supply to be used. The switch would be in the positive circuit. Nothing wrong about doing that as it would not be a series tap. Think about that. Apples & Hand Grenades.

Many hours working with Cheapos Meanwells & Megawatts have convinced me the toroid chokes are overwhelmingly the majority heat producers. Capacitors, bi polar transistors and Schottky rectifiers absorb radiated and convected heat. I am ready to do a roof reinforce and mount a serious 120mm fan with appropriate grilles. External. Right atop the chokes. And the circuit board versus case openings is a real Larry, Curly, and Moe design. What has happened to intelligent thermodynamics designing? One single 1/2" vent hole adjacent to those neighboring chpkes would improve cooling dramatically. The entire starboard side has nothing on it. Oh by the way, this isn't theory - dumping from 113 F internal to 91 F ain't chicken feed. The 120 mm fan is a plan the hole is a reality.

[landyacht318]

MEXICOWANDERER wrote:
If a Megawatt stays at full output for an hour this is no stinky bueno.

I use my Meanwell rsp-500-15 as a bulk charger, absorption, float charger.

At its maximum output(40 amps), it does get hot.

I have enhanced airflow through and over unit, and added more heatsinking and can usually keep it below 120F at maximum output.

I believe Mex's quoted words above are not only to indicate 3 stage converter X is likely to drop to float, or to a lower absorption voltage( thus slowing charging) while the batteries could accept 36+ amps, but that the Megawatt at 36 amp output for and hour might overheat the unit.

Those considering using these as a bulk charger, not just as an Absorption charger to take over when the converter decided to drop voltage while generator is still running, need to consider increasing heat removal from Megawatt/Meanwell to promote longevity, especially in hot ambient temperatures.

I have a thermocouple on the inside of my Meanwell on a heatsink. Ambient temperatures have a Huge affect on internal temps. At 70F it rarely exceeds 106f at 40 amps output. At 90f it will easily climb to mid 120f at 40 amps output, and that is with extra fans and more heatsinking, and airflow over the whole unit.

Once amps drop to less than 32 the heat the Meanwell makes is back down below 100F. Those 8 extra amps really cause a lot more heat.