Author Topic: What kind of resistor is marked "RU" (Read 11087 times)

zap · « **on:** June 09, 2011, 08:51:11 PM »

I've got a blown resistor in a 48v SLA charger... at least I assume it was a resistor.
Here's a picture of the board, oval indicates object that released the magic smoke... accompanied with a rather dramatic flash (ignore the frayed wire from "line in", it's not long enough to have reached and shorted):

Here's the trace side, (I mirrored the image to make everything stay in the same position) purple oval is the same blown resistor(?), orange circle is a capacitor lead that at some point in time had been pushed hard enough to rip the pad from the trace (causing the resistor(?) to blow?:

So...
What does the designation "RU" stand for?

And...
Anyone want to give a guesstimate on the value of the "RU"?

nick1234 · « **Reply #1 on:** June 09, 2011, 09:29:19 PM »

that 2 cent resistor is replacing a transformer if you do not want to see it blow in the future add a transformer at least with a transformer you have isolation from line grd. that's why it blew and you output will be safe from a floating ground put a jupper in is place and add a transfomer of the voltage your AC input requires
hope i am helpful

rossw · « **Reply #2 on:** June 09, 2011, 09:36:28 PM »

Appears to be in series with the mains - almost certainly to minimise the inrush current through the bridge and filter caps when the unit is first plugged in. I've frequently seen a NTC thermister in this role, but whats left of yours doesn't look like it was one.

Without knowing the power of the charger, or the mains voltage it'd be hard to guess the value of the resistor.
Making an educated guess "backwards" - lets say its a 48V/2A out, and 240V IN.
That's 100W out. Needs 100W in, or 400mA
If it was a 1R resistor, that would dissipate 160mW
If it was a 2.2R it'd be 350mW

They're certainly in the "order of magnitude" I'd expect.

If it was 0.1R or less, I'd be doubtful it'd provide any (meaningful) surge protection, and if it were much higher resistance it would dissipate far too much power.

zap · « **Reply #3 on:** June 09, 2011, 09:51:02 PM »

Thanks nick and rossw.
I should have put the full specs...

Input: 90-130vac

Output: 48vdc 2.5A

rossw · « **Reply #4 on:** June 09, 2011, 10:27:05 PM »

Quote from: zap on June 09, 2011, 09:51:02 PM

Thanks nick and rossw.
I should have put the full specs...

Input: 90-130vac
Output: 48vdc 2.5A

The value is going to be around half what I estimated then, I thought the blue/brown hinted at a 240V device. Never mind.

As for nicks advice - the resistor is *NOT* doing the job of a transformer.
This is a switchmode supply, the resistor is not just a voltage dropping element.
Replace it with a link and you WILL cause problems.
You can't really replace it with a transformer either, the SMPS is going to expect a high voltage DC on the primary side.

That the resistor disintegrated as it did suggests to me that the chopper transistor is also shot.

David HK · « **Reply #5 on:** June 09, 2011, 10:58:39 PM »

Could the R be an F which would give the start of Fuse?

David in Hong Kong

zap · « **Reply #6 on:** June 09, 2011, 11:40:50 PM »

It's definitely RU1. That's part of what had me confused... I can't recall seeing an "RU" designation on a board before.

Thanks again rossw. So you say half the value and you said "1R" and "2.2R". Should I assume you meant 1Ω and 2.2Ω?

rossw · « **Reply #7 on:** June 09, 2011, 11:58:54 PM »

Quote from: zap on June 09, 2011, 11:40:50 PM

Thanks again rossw. So you say half the value and you said "1R" and "2.2R". Should I assume you meant 1Ω and 2.2Ω?

"R" is one of the international standards for describing resistance in the "ohms" range, so yes "1R" is 1 ohm, 2.2R or 2R2 would be 2.2 ohms in the same way 3K3 is 3.3 kilohms and 4M7 is 4.7 megohms.

joestue · « **Reply #8 on:** June 10, 2011, 01:23:53 AM »

That electrolytic near the edge of the board thats not even in the right holes... does this run off dc?

that resistor that blew is supposed to be an NTC inrush limitor.

you'll need to replace it with at *least* a 1/2 watt resistor. it doesn't take much energy to burn out a resistor, and when charging up a cap, half the energy ends up in the resistor.

mab · « **Reply #9 on:** June 10, 2011, 05:09:23 AM »

Quote

That electrolytic near the edge of the board thats not even in the right holes... does this run off dc?

It looks like a 240v psu design that's been adapted to run on 120 - with a capacitor in the 'right' holes the ac will be full-wave rectified into a single capacitor. As it is it works as a voltage doubler.

It also looks as though they've had to leave out the supply filter components to make room for the 2nd capacitor - doesn't inspire confidence.

I would second the opinion that 'RU' ought to be an NTC, but appears to be a plain resistor.

m

Bruce S · « **Reply #10 on:** June 10, 2011, 10:13:22 AM »

ZAP;
Is that the 48V charge for the e-scooter? It looks exactly like the charger of Amy's e-scooter and it is 48V as well.
I will open it back up and get the value for you this evening.
Bruce S

zap · « **Reply #11 on:** June 10, 2011, 10:48:15 AM »

Yup Bruce, it's from the scooter.

Have a look when you get a chance and let me know... it's not a pressing issue right now. Plus that scooter has over 1300km showing and I'm pretty sure this was the charger that was used so I'm fairly certain it's charged up those batteries just fine more than a few times

Muy apreciado to all for the help.

Bruce, I also want to try and get the old controller working... I may have some Q's for you on that also

David HK · « **Reply #12 on:** June 10, 2011, 07:23:27 PM »

You're in luck chaps. The attached URL seems to show a similar or identical version of your charger.

http://www.electricscooterparts.com/48vchargers.html

Unfortunately there is no circuit diagram but you could try contacting the supplier.

What this web site does provide is an explanation of the wiring harnesses for different motor scooters and i have found it to be a very useful reference bass for many items associated with e-scooters. make sure you click on Big Picture for wiring harness plug connections.

http://www.electricscooterparts.com/speedcontrollers24volt.html

Repair Help is on the Menu and may be of assistance.

David in Hong Kong

zap · « **Reply #13 on:** June 10, 2011, 08:50:41 PM »

Thanks David, that site does have a lot of scooter stuff.

You might like this site also, http://tncscooters.com/partsdb.php?type=ES, it has a lot of specifications on controllers.

And speaking of controllers... are you any good at translations?

Bruce,
If you still have your charger open, has "R12" been clipped out on yours?
Also, what voltage does yours get to? I saw this one all the way up to 58.6vdc and it still wasn't shutting off.

David HK · « **Reply #14 on:** June 10, 2011, 09:25:07 PM »

Zap,

I am actually Anglo Saxon British but my wife is Chinese and we have a very fluent tri-lingual daughter.

I will ask my daughter for a rough translation and put it in this thread later.

For info I have often seen U1 marked on PCB's and also U2, U3, U4 and so on. I think its a PCB designers reference to Upper (as on a PCB) for various item placements.

R is I think the reference for Resistor.

Your making some progress.

David in HK

zap · « **Reply #15 on:** June 10, 2011, 09:41:24 PM »

Quote from: David HK on June 10, 2011, 09:25:07 PM

I am actually Anglo Saxon British but my wife is Chinese and we have a very fluent tri-lingual daughter.

I will ask my daughter for a rough translation and put it in this thread later.

Wow... thanks... I was mostly kidding. If need be I can get a better picture.

Much is self evident:
25amp
48v
I'm not quite sure on the "(+12V) but I'm thinking it might have a 12v tap even though this scooter has a separate dc/dc converter(not working).
"1V-4V" I believe is the throttle voltage.

Yes, making some progress. Hopefully Bruce's charger is a close match.

ghurd · « **Reply #16 on:** June 10, 2011, 11:20:26 PM »

Quote from: David HK on June 10, 2011, 09:25:07 PM

and we have a very fluent tri-lingual daughter.

David,
Completely off-topic,
Tri-lingual? May I ask what they are?
It amazes me the human brain can be "wired" to speak fluently in languages so radically different in syntax (I can not find a better terminology).
G-

David HK · « **Reply #17 on:** June 11, 2011, 01:53:12 AM »

Ghurd,

My daughter is fluent in English - written and spoken - and she has a UK University degree.

She is fluent in Mandarin or Putong Wah which is the official language of China. She is also fluent in the Cantonese which is the local provincial dialect and she can read a Chinese newspaper.

She is also quite good at spoken French.

I wish I was that good.

Regards,

Dave

Boss · « **Reply #18 on:** June 11, 2011, 01:36:38 PM »

Quote

She is fluent in Mandarin or Putong Wah which is the official language of China. She is also fluent in the Cantonese which is the local provincial dialect and she can read a Chinese newspaper.

She is also quite good at spoken French.

I wish I was that good.

Wow she sounds quite talented
I'm not even good at my mother tongue, English

SparWeb · « **Reply #19 on:** June 13, 2011, 04:01:24 PM »

You guys all missed the joke. The circuit board designer put that designation there on purpose to indicate that the resistor is a mistake.

The RU1 label means that's the resistor you're supposed to "ruin".

Boss · « **Reply #20 on:** June 13, 2011, 05:40:59 PM »

Back when I was troubleshooting circuit boards I found one with the word "Secret" typed in above a momentary contact switch on a stereo front panel. I finally surmised it was a Chinese to English translation error. It was supposed to read select, apparently someone verbally translated the word "select," dropped the "L" replaced it with the more prevalent "R" in Chinglish, at least that's the way I tell this story. Who says electronics trouble shooting is dull?
You can bet every one of my buddies came up and pressed it at least once. What's this do?

If I told you it wouldn't be a secret would it?
I loved you PC board smiley face

zap · « **Reply #21 on:** June 13, 2011, 09:21:03 PM »

Nice catch sparweb. I never noticed the "ru-one".

Bruce S · « **Reply #22 on:** June 15, 2011, 12:16:09 PM »

Zap;
Sorry for the long delay, work got uh insane is the best word I can find

I opened our unit and it is no where near what you have. This unit doesn't even have any marking other than the values and those don't follow any real standard markings

I do not have have the "have a nice day" picture on it

Bruce S

tanner0441 · « **Reply #23 on:** June 15, 2011, 01:23:50 PM »

Hi

When my job involved servicing electronic equipment, if I had found a smiley face and have a nice day in the solder mask I think I would have crapped myself wondering what I was in for....

ICs with the tops ground off, dummy sections on the board, were normal I have even padded out eproms with nulls and loops myself, but a smiley face and have a nice day is the ultimate. I wish Id thought of it.

I hope you sort your problem out..

Brian.

dbcollen · « **Reply #24 on:** June 15, 2011, 02:09:04 PM »

Most of the older trace inverters I have opened had the smileys, and a story told in different sections of the board. DR1524, and DR2524s

Dustin

zap · « **Reply #25 on:** June 15, 2011, 04:45:12 PM »

Thanks any way Bruce. I asked over on e-s and nada also... maybe I'll ask again in a different category over there.

Bruce S · « **Reply #26 on:** June 15, 2011, 06:03:03 PM »

Quote from: zap on June 15, 2011, 04:45:12 PM

Thanks any way Bruce. I asked over on e-s and nada also... maybe I'll ask again in a different category over there.

ZAP;
I did a closer look at where that RU is located with respect to how mine is assembled

I do have on my board a resistor that I usually only see on better assembled units.
IT is what we used to call ZERO Ohm or Pico-fuses. Mine looks to be rated for 5 watts easy as big as it is.
The marking are Brown, Black, Gold, Silver.
There are a few items in the medical world that still uses these at the front end of the charging systems and on the old daughter boards of SDLC modem boards.
In a pinch we would use a 30ga wire in place to get the job done while waiting for a replacement board.
I can find one of two of these off the shelf if you want to get them a try, they are the more traditional 1/4watt size though.
Sure hope this helps!!
Bruce S

zap · « **Reply #27 on:** June 16, 2011, 08:58:54 AM »

The zero ohm does make sense because over on the sphere I was told by one guy that he's repaired a few different 48v chargers replacing the blown resistor with just a jumper.
A couple of others said it's a inrush current limiter that I should be able to scrounge from an old pc power supply which pretty much would confirm rossw's initial observation and seems to support what wikipedia has to say about them "Negative temperature coefficient (NTC) thermistors and fixed resistors are often used for this." since it certainly looks like a resistor and not a thermistor.

Bruce S · « **Reply #28 on:** June 16, 2011, 09:48:59 AM »

Forgot to add,

Yes the charger get UP there, I've tested this one in an open voltage just to check and I had 60Vdc.
Loaded and depending on which battery bank I have in it, and how discharged they are it settles down quickly once I plug it in.
For the NiCd that I built for it, I have 4 Ghurd dump controllers on it and 4 separate wire pairs coming off the HF system. This because I needed to do something with the extension cord a "visiting" puppy used for cutting teeth with

.

Question? was the charger working and blew this? or was it this way when you got it?
There were some charger like your and mine that had the computer plug unit wired backwards that would cause the same problem.
Cheers;
Bruce S

zap · « **Reply #29 on:** June 16, 2011, 11:15:26 AM »

Other than the slightly high voltage it would take the batteries up to, the charger was working fine when I first tried it. I think I used it 2 or 3 times before the flash.

That's why I was asking if it was most likely the lose capacitor leg that made it go phzzzttpop since it seemed to work fine before.

Bruce S · « **Reply #30 on:** June 16, 2011, 11:39:32 AM »

Quote from: zap on June 16, 2011, 11:15:26 AM

Other than the slightly high voltage it would take the batteries up to, the charger was working fine when I first tried it. I think I used it 2 or 3 times before the flash.

That's why I was asking if it was most likely the lose capacitor leg that made it go phzzzttpop since it seemed to work fine before.

You also said you had another unit?

zap · « **Reply #31 on:** June 16, 2011, 12:03:44 PM »

No, just this one.
I might have said I could still charge them? That was either charging them separately or sticking them on 3 dollar charger.

zap · « **Reply #32 on:** June 17, 2011, 11:56:51 AM »

Many thanks to all who replied.

I grabbed an SCK 053 thermistor off of an old computer psu and stuck that in, resoldered the frayed line-in, and scrapped some copper clean around the capacitor and resoldered that.

Did a test run and all seemed well, put it all back together and plugged it in. I heard the fan running but now the led weren't lighting up

Heh... I had screwed the lid on wrong

Turned the lid 180Â°, plugged it in and all is well.

It still takes the batteries up higher than I'd like, it's throttles back to float at exactly 59v

... I'd rather see it somewhere around 56v max...
If anyone has any ideas on that...

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Author Topic: What kind of resistor is marked "RU" (Read 11087 times)