Converter In-Rush Thermistors etc, UPDATE -4

UPDATE on 17 Nov, Update 2 on 22 Nov, Update 3 on 16 Jan 14,
Update 4 on 19 Oct 14.
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In a recent thread there was mention of how you can wreck your gizmo (in my case a converter) by turning it off and restarting it again before the capacitors have finished unloading----if I was understanding that discussion.

So I am worried I am going to wreck my nice PowerMax 100 amp converter doing that.

Background is that last year I had one of these and had the top off so I could adjust its voltage with the internal pot they have. Somehow at one point after some weeks of using it, the in-rush current thermistor burst into flames and that was that.

PowerMax sent me a new "beefier" thermistor which they said would also be used in the newer 100 ampers. I got that in and had that going for a while and then I think when starting and stopping and restarting right away (maybe that was it, not sure) that thermistor over-heated and fell to bits.

I am wondering if it was operator error in starting/ stopping sequence that did for both thermistors.

I do see on the voltmeter that after you shut off the converter (when disconnected from battery), its voltage tapers down for a good time rather than drops straight to zero, and from the discussion mentioned above, I understand that is the capacitors "unloading." So now I am wondering if I blew the new in-rush thermistor last year by restarting the converter under full load of 100amps too soon?

The in-rush thermistor seems to be on the 120v input side while the capacitors that unload are on the DC side some distance from the thermistor on the circuit board so I am not sure how they relate.

BTW PowerMax was kind enough to help me out replacing my ruined converter and I now have a fancy new prototype ( I guess) version with an external voltage pot this time. I promised not to take the top off and poke around inside it :)

However, the way I do my recharge, it can happen that say the Honda pops its breaker due to other loads added besides the converter, and I restart the Honda before the converter capacitors unload. Even with a normal start, the converter sometimes makes a snap sound like my big inverter will when disconnecting and connecting, which is capacitors according to folks here who have commented on that. (except how can the converter ones snap on start-up if they are already unloaded?)

I have been using this new 100amper for a while now and nothing has gone wrong. But I am scared to death of screwing up my nice converter by some sort of mystery operator error if that is what it was. I can't avoid "doing it again" when I don't know what I did!

Thanks

MEXICOWANDERER
Explorer
May 29, 2013
Do yourself a favor BFL13, and put a 1 or 2 Farad automotive stereo sound system capacitor right next to the converter. An electrical "KONI"
msiminoff
Explorer II
May 29, 2013
Hi BFL,

I've had a similar concern... When I turn on my battery disconnect switch(es) there is a large inrush current when the capacitors in my inverter charge. In an effort to reduce arcing & pitting of the contacts in the switch I built a simple/cheap push-button activated pre-charge circuit that allows the cap's to charge slowly through a high-current resistor before I close the battery switch.

Of course this does nothing on the AC side of the inverter/charger.

Cheers,
-Mark
KJINTF
Explorer
May 29, 2013
Hi BLF,

I have had an oppertunity to repair as many as 20 to 30 converters over the last couple of years.

90% of the failures have been the input side 250Vdc 1,000ufd caps (typically there are at least three in parallel). Most switching converters ingest the 115VAC then with a full wave bridge rectifier get about 160VDC on the input side of the switching supply.
Yes from what I have seen plugging and unplugging the source AC supply has contributed to the failures. That said many were defective caps in the first place. I would venture a guess that your thermister was previous to the bridge rectifier on the AC side of things. Surge currents do strange things and are NEVER any good for electronics devices.
Salvo
Explorer
May 29, 2013
I don't believe that's true. Voltage tapers after converter turn-off due to the battery holding up the charge, not converter capacitor. The battery is one huge capacitor.

Your previous converter failed either due to poor design or a bad part. Don't worry about frequent on/offs.

Sal

BFL13 wrote:

I do see on the voltmeter that after you shut off the converter (when disconnected from battery), its voltage tapers down for a good time rather than drops straight to zero, and from the discussion mentioned above, I understand that is the capacitors "unloading." So now I am wondering if I blew the new in-rush thermistor last year by restarting the converter under full load of 100amps too soon?
time2roll
Nomad
May 29, 2013
It has a three year warranty. Try to just use it normal.
If the solar thing is working out maybe leave the generator at home and disconnect the converter.
Pack more fishing gear or other toys.
BFL13
Explorer II
May 29, 2013
Thanks for the replies. Perhaps there is a best way to do this

(Salvo, the DC voltage tapering seen after shut down is with no battery connected to the converter, so it is all internal)

So here are the steps I need to do in no particular order, and then please suggest the best sequence for the converter's health.

-Start Honda, plug converter into Honda
-turn on converter with its own switch it has, adjust the external voltage pot without the battery connected (or you can't tell what voltage you are setting on the converter due to battery voltage getting mixed in)
-clamp on to battery bank and hear the Honda rev up

Here is a picture showing it with the external knob, the on/off switch, and the little voltmeter on the top. It is clamped to the battery bank and plugged into the Honda

One thing I was doing was get the converter voltage set and then turn off the converter, then clamp on, and then turn the converter back on---this is another time where I could be turning it back on too soon

I am unclear if the converter should be on and then clamp on to the batteries or if you should be clamped on first and then turn on the converter.

Afterwards, I don't know whether to just unclamp and then turn off the converter, or to turn it off and then unclamp from battery

If I do have to restart, should I unclamp (to read converter only voltage) wait till the converter DC voltage has dropped all the way down or can I restart when it is part way or mostly down, what?

I don't mind if the sequence is awkward as long as it keeps the converter from making smoke signals :)
KJINTF
Explorer
May 29, 2013
The output voltage does indeed "bounce" several times after it's turned off and completely disconnected from the battery bank, it's normal the switching supply is attempting to get it's needed power from the input side caps which are discharging quickly. Typically very few if any output side caps other than the EMI stuff.
Salvo
Explorer
May 29, 2013
The best sequence for converter health is to turn it on and off 50 times every few seconds. If it fails, either they still didn't get the design right or you got more bad parts.

Some 30 years ago, I knew an engineer who would run his newly bought TV in the cardboard box for a few hours. If it still runs, it's a good TV & good design. Otherwise, back it goes.

Sal
time2roll
Nomad
May 29, 2013
In normal use as an installed converter it would always be connected to the battery when power connected or disconnected. I would try to use it in that mannor.

OK maybe not if you have a battery disconnect switch. But still a few sparks when connecting should be avoided IMO.
MEXICOWANDERER
Explorer
May 29, 2013
My kind of humor. Thanks Salvo!