Photo, is this a diode or a resistor? temperature gauge 1975 300D - Page 4 - PeachParts Mercedes-Benz Forum

patbob · #46 08-28-2011, 02:26 PM

Quote:

Originally Posted by 1975300D

I will order one online. I tried sourcing these things locally, and no one carries them. At least no one who is mentioned on google.

Unless you live in a tiny town, I'd be suprised if there wasn't some place you could get one locally, 5W 68 ohm is a pretty common size. Perhaps try looking electronics parts suppliers up via the yellow pages instead of google. Places like that sell to the industry, and so don't always have a large, easily found, web presence with high google page ranking.

1975300D · #47 08-28-2011, 03:57 PM

Hi Pat, I actually called two electronic parts suppliers and both told me they didn't sell resistors and didn't know of anyone who did.

1975300D · #48 08-28-2011, 03:59 PM

I think I measured an intact one on the same board and came up with 68. I strung two or three together to get 68 (Forget the values but I got them at RS.)

If you got them at radio shack, then they weren't 5w, but like a 1/4 watt. I checked them out and they had the right resistance but the wattage was wrong. Maybe that is why you have had no success.

1975300D · #49 08-28-2011, 04:03 PM

Quote:

Originally Posted by JimF

Just happened to see your thread . . .

If this is a "current sense" resistor and it's "5W", then I doubt that it's "68 ohms"; most likely it's a "0.68 ohm". .

Here's a 0.68 ohm, 5W, axial resistor: cost is $1.20 each:
http://www.mouser.com/ProductDetail/Panasonic/ERX-5SJR68/?qs=ykEKLGTiBczSOwfH5bnJqw%3d%3d

I don't know if that makes sense. The formula is P = V²/R. Therefore using a voltage of say 12, and a resistance of only .68, would give you a wattage of 211!

JimF · #50 08-28-2011, 05:28 PM

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Yes, but who said it's twelve volts?? That's your assumption and it's most likely wrong b/c if the meter measures "temp", then it's a much lower voltage.

What I wrote was, " . . if it IS a 5W resistor. . ", meaning that if you are SURE it's a 5W resistor, I really doubt that the resistor was 68 ohms.

However, I've given you a lot of choices so you can buy some w/o breaking the bank . . . and you can buy small quantities from them w/ no problems. RS has nothing anymore!

A meter responds to "current" and that's what a 'current-sense' resistor does; makes sure that the current flowing thru the meter won't fry it!

You can test it yourself; get some resistors and a low voltage battery. Introduce the current with a known voltage and resistance. When the meter is adjusted for full-scale deflection, you can calculate the meter's sensitivity.

I'll bet it's "1ma" full scale????

1975300D · #51 08-28-2011, 05:33 PM

Yes, but who said it's twelve volts?? That's your assumption and it's most likely wrong b/c if the meter measures "temp", then it's a much lower voltage.

I've been told on this thread that the voltage is somewhere between 12-14 volts. So I am going by that. Also I have had two people tell me they measured the resistance at 68.

punkinfair · #52 08-28-2011, 09:44 PM

if you can make it downtown you can try supremetronic on college street or active surplus on queen street. for sure electrosonic will have something also, they are bit harder to buy from.

1975300D · #53 08-29-2011, 01:57 PM

HI Punk, I called electro, and yah, they only want to sell you $25 worth and you have to have it shipped to your house even though I am 15 minutes away. lol. A very expensive 59 cent resistor.

Active surplus has nothing.

Digi-key wants $35 to ship a 59 cent resistor and 5-10 days to get here.

And Supreme, the person who knows about resistors isn't in and they don't know when he will be.

You'd think a metropolis of 3.4 million people would have a place that you can buy a resistor from. Makes me think I should open up my own store. Resistors R Us. Or Resistor Depot.

Orv · #54 08-29-2011, 02:00 PM

5W was a conservative estimate on my part; it does look a little small for a 5W resistor, but too large a wattage rating doesn't hurt anything and I didn't want to guess low.

It might be a 1 watt resistor, but it's hard to say without measuring the current or seeing the whole circuit. It looks too big to be 1/2 watt.

A little math shows that in a 12V system the dissipation in a 68 ohm resistor can't be much higher than 2 watts. (And I know it's 68 ohm, at least on my car, because I measured it.)

Mouser is great, but I think they have a $20 minimum order. Digi-Key will do smaller orders but tacks on a service charge.

1975300D · #55 08-29-2011, 02:34 PM

I just called another place called Crystal Electronics, listed as an electronic supplier.

Phone rings:

She: Crystal Electronics

Me: Hello, I'm looking for a resistor. Do you sell resistors?

She: Click.

I called back, and she refuses to pick up the phone now.

Did I say something wrong?

punkinfair · #56 08-29-2011, 03:36 PM

Quote:

Originally Posted by 1975300D

And Supreme, the person who knows about resistors isn't in and they don't know when he will be.

they have a lot of components there, don't give up.

Rafi · #57 08-29-2011, 04:00 PM

Newark has it

http://www.newark.com/ohmite/25j68re/resistor-wirewound-68ohm-5w-5/dp/64K8323

1975300D · #58 08-29-2011, 04:02 PM

Thanks Rafi, but I'm looking to find something locally that I can pick up. Online is very expensive because the shipping costs are huge and I have to wait 1-2 weeks to get it.

Rafi · #59 08-29-2011, 04:05 PM

OK, make one yourself. Do you have a spare fuel level sender ?
cut the wire and and wind it on a wooden dowel (do not let the loops touch each other), check the resistance and cut ot as needed then epoxy it.