Hyena wrote:My buzzing ONLY came from the R37 resistor mod. The second I touched another resistor across in in parallel the current dropped and it started the arcing/buzzing sound. Remove it and the current shoots back up and the arcing stopped. The packs I was charging are also brand new, but as I said they happily charged silently at the full current output from the power supply so in my case atleast its not the packs causing the buzzing (and probably less likely in your case too, unless one cell is madly sucking current or something ? )
Oh and yeah I have the earth connected - well, the earth connector to the AC power lead earth. I haven't physically run a lead from that earth terminal to the side of the case. to the I have a CFL light over my work bench that buzzes quite loud sometimes, but a sharp whack fixes it. Hmmm, maybe I should try that with the PSU next time...
heathyoung wrote:Have you post-mortum'ed the old PSU's? I wouldn't mind a look at some of your dead-'uns to see what happened...
mwkeefer wrote:The current jumping (or peaks) when the fan comes on is exactly what I explained previously - when the fan kicks on, it draws power from the same isolated and scaled voltage power source that the TL494 uses... this additional current draw causes the voltage being supplied to the DTC (Dead time control) to drop. This pin works in INVERSE mode so 0v input = MAXIMUM CURRENT, 3.3v on the pin = 0 CURRENT. Since the additional load of the fan causes a voltage drop, that is the reason the current spikes up when the fan switches on.
The part I just for the life of me don't understand (read that as I'm not sure what value components to install here) is involving D18 and Q7. In my conversations (limited as they were, the tech guys at meanwell are awesome - sales at Meanwell USA isn't even worth bothing with and I was inquiring with regards to 1000 unit purchase, the sales biat** referred me to mouser who had 2 in stock?) with Meanwell tech, he was very hesitant (I think he could get in trouble) but at least informed me the transistor is of type NPN.
Vanquizor wrote:With the concerns about instability with the fan cycling wouldn't the quick and dirty be to just force the fan to run 100% of the time? Would still give predictable output and it can't hurt life cycle to keep things a little cooler.
Suggestions on the best way to accomplish this?
fechter wrote:Part of the problem might be if you're increasing the output voltage too much over stock. It really needs a new transformer wind to push it really far
fechter wrote:Part of the problem might be if you're increasing the output voltage too much over stock. It really needs a new transformer wind to push it really far. A sidestep approach is to simply use two or more supplies in series to get the desired voltage. With two in series, I suspect you could get away with just keeping one stock and mod the current limit on the other one. The one with the lowest limit will do all the limiting anyway. You may actually need to turn down the voltage on one in this case to get what you want.
Hyena wrote:Mike, I picked up some 1k, 2k and 200 ohm 10 turn pots + a handful of 100 and 200 ohm resistors yesterday afternoon to do pretty much the exact thing you just described! I was just going to put the 2k in svr1 to allow the voltage to go a bit lower. What was R25 before you changed it ? Mine is 22k I think. If yours was the same and you've dropped 7k that sounds like a fair bit (assuming your R25 is in series with SVR1) Or is this big drop what's enabling you to go to 63v ? (plus upping the zener under the transformer of course).
As for higher voltage mods, if the transformer is even up to it you'd have to swap out the front caps atleast. Mine are only 63v units so you're running right at the upper limit of what the 48v models can do.fechter wrote:Part of the problem might be if you're increasing the output voltage too much over stock. It really needs a new transformer wind to push it really far
I don't think so Fechter, at least not completely. Mine has all the same symptoms Mike is describing and unmodified it's running at the lower end of its range (42v on a 48v unit)
mwkeefer wrote:Actually... my 48v units come with 100v caps on the output already (sure-electronics)
My unit was different, R25 was 2k I think... I don't remember anymore = )_
I'll look at your PCB pics in the AM and figure out what points to check for impedance... then we can bump the unit either way or just expand the range.
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