Megawatt Dissection & Notes
This is "Jim In Denver's" unit. Circuit board fuse found to be "good" One 330 uf cap has a domed top. My ESR tester located far far away. Bridge rectifier tested good Bi-polar transistors: One s...
Forum Discussion
Why oh why oh why. Is it stupidity?
Just finished diagnosing a wheeled battery charger. Extra high transformer settings are marking "Engine Start". Guess what? "Engine start" imposed a 117 PRE-measured amperage from 11 lb transformer. Guess what? They used 40-amp DO-5 stud rectifiers. 100 PIV. Eighty amps capacity, 117 amp load across the worst Inductive reactance load imaginable. Shorted both rectifiers. 0.017 ohms both directions.
Yeah it blew the switch, yeah it fried two inches of secondary winding on the transformer. The selector switch is FUSED in the cranking selection setting.
All because the manufacturer chose to "save" about four dollars and change on rectifiers. The owner of the charger is going to purchase a Sola. I will install IDENTICAL size rectifiers, but rated 70-amps @ 800PIV. And use a FINNED heatsink, not the 3" x 7" flat plate the manufacturer uses.
In their $700 wheeled charger ASSOCIATED uses a sandwich of a half dozen 50-amp button rectifiers rated 200PIV per center tapped secondary transformer lead. Six hundred amperes total capacity.
I freakin' refuse to settle for electrical gear that a 5th grade grammar school student could out-design.
John Marles (Megawatt), bless his heart sent a pair of FORTYCPQ 100 bi-polars. (40CPQ 100) to replace the THIRTY CPQ 100 bi polar transistors. (30CPQ 100). I will settle for the highest "I" rated and lowest vf rated TO-247 package bi-polar transistors I can get my grubby hands on.
And yes, I have suppression discretes now for both ends of chargers and power supplies. MOVs, TVRs, and for AC, the GDT.
I demand Berquist A2000 sil-pads for the Bi-Polars. I shiver at it's cost.
I did find electrolytics rated 1000 volts 680 uf, in the catalog. QUOTE "100-year lifespan at 100c" Cost? A mere $257.00 ea plus tax and shipping.
"Dyslectics Of The World UNTIE"
TO-247 Pkg SCHOTTKY rectifiers. Thinking about seven things at once including a USA air ambulance rescue of an ex-pat on life-support 200 miles from here. Who says being retired means being bored?
Now back to shopping...
Just finished diagnosing a wheeled battery charger. Extra high transformer settings are marking "Engine Start". Guess what? "Engine start" imposed a 117 PRE-measured amperage from 11 lb transformer. Guess what? They used 40-amp DO-5 stud rectifiers. 100 PIV. Eighty amps capacity, 117 amp load across the worst Inductive reactance load imaginable. Shorted both rectifiers. 0.017 ohms both directions.
Yeah it blew the switch, yeah it fried two inches of secondary winding on the transformer. The selector switch is FUSED in the cranking selection setting.
All because the manufacturer chose to "save" about four dollars and change on rectifiers. The owner of the charger is going to purchase a Sola. I will install IDENTICAL size rectifiers, but rated 70-amps @ 800PIV. And use a FINNED heatsink, not the 3" x 7" flat plate the manufacturer uses.
In their $700 wheeled charger ASSOCIATED uses a sandwich of a half dozen 50-amp button rectifiers rated 200PIV per center tapped secondary transformer lead. Six hundred amperes total capacity.
I freakin' refuse to settle for electrical gear that a 5th grade grammar school student could out-design.
John Marles (Megawatt), bless his heart sent a pair of FORTYCPQ 100 bi-polars. (40CPQ 100) to replace the THIRTY CPQ 100 bi polar transistors. (30CPQ 100). I will settle for the highest "I" rated and lowest vf rated TO-247 package bi-polar transistors I can get my grubby hands on.
And yes, I have suppression discretes now for both ends of chargers and power supplies. MOVs, TVRs, and for AC, the GDT.
I demand Berquist A2000 sil-pads for the Bi-Polars. I shiver at it's cost.
I did find electrolytics rated 1000 volts 680 uf, in the catalog. QUOTE "100-year lifespan at 100c" Cost? A mere $257.00 ea plus tax and shipping.
"Dyslectics Of The World UNTIE"
TO-247 Pkg SCHOTTKY rectifiers. Thinking about seven things at once including a USA air ambulance rescue of an ex-pat on life-support 200 miles from here. Who says being retired means being bored?
Now back to shopping...
