MegaWatt S-400 as boost charger up in smoke

Question

It looks like this discussion is archived and can't be reopened (another example of some topics being locked up that are best kept open because the solution remains relevant), but that's another topic for another day. Today I want to warn anyone not to make the same mistake I did by following an old post here, and to supply the details to hopefully prevent someone else from repeating it and burning up a relatively expensive device. I was following a philosophy stated here of using a Megawatt S-400, setting it to 14.8V and attempting to change a battery while using a wind up timer to energize the MegaWatt for a short amount of time.

I had two Costco GC2's in series in my coach that had discharged to about 85% according to my battery monitor when I started the generator. I then twisted the timer for 40 minutes and began to read while I waited. I noticed 36A charge reading right off the bat on the battery monitor so I decided to check the voltage on the actual battery terminals to see if anything was awry. (I had set the MegaWatt to 14.8V via the adjustment pot reading it with no load.) The voltage on the battery terminals read 14.3V which . After about 15 minutes of rapid-charging I smelled something a little odd and by 30 minutes the power supply had shorted out internally and tripped the GFI.

Calling the manufacturer, the support person said that the charger would only produce 30A long term and that I burnt it up by not following the suggested amperage limitation. (There is no built in regulator for the device he stated.)

Anyway I have a boat anchor now so other people who want to build a single stage "boost only" charger from previous suggestions in this forum should keep this in mind if your 14.8V boost supply is rated at under 30A in reality as this one is (apparently).

landyacht318 · Answer

I used a 23$ budget Megawatt coined the cheapowatt.

Rated for 30 amps it would output close to 38 amps. Over 36 amps it made this sound which said things were not right.

So I had to limit amperage to 36 or below by starting lower on the voltage scale and twiddling the potentiometer upward often. to keep it in the 30 to 26 amp range.

i had rigged up a better potentiometer, i had increased heat dissipation with a better fan and some better mating of heatsink with casing.

Eventually i got tired of the pot twiddling, and i set it to 14.8v unloaded, hooked it to a depleted battery and away it went, making that 'not right' noise.

It lasted 17 minutes.

I then bought the Meanwell RSP-500-15, and have been using that since september 2014 as a 40 amp charger converter floater equalizer, everything.

I have increased its ventiation and heatsinking, and it has thousands of hours on it. Its voltage range is 13.12 to 19.23v.

No personal experience with the Megawatt. I suspect the fans re culprits in the failure. The internal 60MM fans have a lot of restriction behind and in front of the fan. I had moved the fan to the exterior of the casing to reduce restriction.

My MEanwell has a 40 and a 60MM fan on the lid, 40MM blowing in 60MM sucking out. The MW comes with a very loud powerful 40MM fan, but my ther fans keep it off below 32 amps of output.

Send your 'boat anchor' to Mexwanderer.

mexicowanderer · Answer

Would you care to do a little investigating to determine "what went wrong"?
Where was the device placed and how did you mount it?
What kind of generator was powering the device? Was the generator loaded or unloaded?
Have you verified the generator speed (frequency) was 55 to Hz?
How about voltage loaded and unloaded?
GCFI Circuit breakers are normally rated for 15-amps. As the green white and black wires enter the Megawatt case, the very first thing they encounter is an axial lead read-precision, fast acting tubular fuse rated 10.0 amperes, then comes a pair of MOVS.

Yes the factory rating of the Megawatt 400 is 30 amps. I have nine of the units. And have extensively modified 3 of them to produce as much as 55 amperes 24/7/365

My interest in this is to determine "What went wrong". Too many units have gone too long on much higher load amperages to consider what happened to your Megawatt "normal". The one that failed to my knowledge was set flat on a hard surface then charged at full capacity of 40+ amperes for days, trying to keep up with several 8-D batteries.

Are you willing to work with me on this? It would involve you shipping the charger to the San Diego area. This is not an offer to gruesomely poke the corpse and see if it twitches.

Check the stuff I listed above on your rig if you would be so kind. There was a $22 dollar junko Chinese clone of this machine that went further and worked harder than your 65 dollar unit and frankly my eyebrows are up to my forehead. But I am an old wizened-fart. I will wait to read your reply before moving on this :) A genuine offer to help...

don_a · Answer

I am currently parked in Antigua Guatemala and would be happy to send upon my return which will be several months from now.   I am driving a 2006 Navion by Winnebago with the stock generator that will power the 18A HVAC with no problem.   I have a combo volt/amp meter on my power source after the transfer unit which shows the characteristics of the power I have switched the transfer unit to.   The voltage from the generator was at 120VAC out of the generator and I didn't make note of the amp reading.   No other appliance other than the Norcold 6xx was running off the generator.  I have two 4/0 welding cables run 10' from the two Costco GC2's in series that run into my louvered cabinet that has to two solid copper bus bars mounted there where the solar, a 2000W inverter (no, it wasn't on and is seldom) and the 2 solar controllers are tied into that bus as well to produce 430 watts. On this day it was heavy cloud cover after 3 days.   There is a 500A shunt from my battery monitor on the negative terminal of the two series battery bank and on the positive terminal has a 300A AGC fuse in line.     The wire going from the bus bars to the MegaWatt is two three foot long 4AWG stranded battery cables with the ends fanned out into 3 smaller twists that are covered in heat shrink and 3 spade connectors soldered on the end of the 4AWG cables to mount to the 3 Megawatt terminals for each DC output post .   The Megawatt is in the same cabinet with a solid louvered door that is about two cubic feet and the door was open during the charging session.

don_a · Answer

The battery monitor is a BMV-700 and was reading 36A for about 10 minutes and along about the time I started smelling something I looked and it was reading 30A.   And another thing, thanks for your reply and offer :-)

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