Determine old resistor from old vehicle - Page 1
Forum section: electronics / beginners

author: jabalv
author_rank: Contributor
timestamp: February 07, 2019, 01:43:27 pm
content: Hi.I have a schema for tractor where there is glower input inlet. There is 12V+12V 24V and R1 to transfer 12V for that glower.But that R1 is in terrible condition and I am trying to understand where can I get such thing and how big value it is.See attached images.Can you please help?

author: ArthurDent
author_rank: Super Contributor
timestamp: February 07, 2019, 02:47:55 pm
content: From the photo it doesn't look like the resistor's zig-zaggy element is broken so you may still be able to read the resistance of the resistor with a multimeter. Ohmite vitreous power resistors may have a close replacement. Other than that a repair shop or the tractor maker would be the place to go.

author: cvanc
author_rank: Frequent Contributor
timestamp: February 07, 2019, 03:45:00 pm
content: Quote from: ArthurDent on February 07, 2019, 02:47:55 pmYup, exactly. It looks like you might still be able to measure the value of your part, so head in that direction and let us know what you find.And post a picture of the tractor! Old tractors are cool. Good luck with your restoration.

author: soldar
author_rank: Super Contributor
timestamp: February 07, 2019, 03:54:18 pm
content: If the glow plug is 12 volt and the resistor is to drop 12 V from 24 to 12, then the resistor is of the same resistance as the glow plug.

author: mikerj
author_rank: Super Contributor
timestamp: February 07, 2019, 04:50:49 pm
content: Quote from: soldar on February 07, 2019, 03:54:18 pmNoting that the resistance of the glow plug will likely increase when running at it's intended temperature compared to cold.

author: Zero999
author_rank: Super Contributor
timestamp: February 07, 2019, 08:13:42 pm
content: Quote from: mikerj on February 07, 2019, 04:50:49 pmThat's true. Connect the glow plug to a 12V power supply, measure the current and work out the resistance, using Ohm's law: R = V/I and use a resistor, close to that value. The power rating of the resistor must be at least V*I, where V will be 12V and I is the current.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: February 10, 2019, 04:09:32 pm
content: Quote from: mikerj on February 07, 2019, 04:50:49 pmThen fire it up directly from a 12 volt battery and see how much current it pulls when hot. That gives you the hot resistance.Sent from my SM-G900V using Tapatalk

author: jabalv
author_rank: Contributor
timestamp: October 29, 2019, 08:19:56 pm
content: Is it really that simple? I did it but numbers kind of didn't match up to me afterwards with what I found in some manufacturer part description.

author: mikerj
author_rank: Super Contributor
timestamp: October 31, 2019, 03:32:26 pm
content: It should be that simple, though you would need to measure voltage at the glow plug terminals to remove errors from cable resistance. What were the numbers you got compared to the manufacturers numbers?

author: AVGresponding
author_rank: Super Contributor
timestamp: October 31, 2019, 04:00:57 pm
content: I think it unlikely that the glow plug runs at exactly 12V, since it would have been simpler for the manufacturer to tap off 12V from the battery string instead of adding a resistor into the equation.

author: viperidae
author_rank: Frequent Contributor
timestamp: November 03, 2019, 07:26:08 am
content: Tapping 12v from a 24v system sounds like a terrible idea to me. You'll end up killing the the other battery, as it gasses out its electrolyte when fully charged, while the other battery is still charging due to bring discharged more.

author: AVGresponding
author_rank: Super Contributor
timestamp: November 03, 2019, 09:22:22 am
content: Not really, glow plugs aren't running constantly; they are heated electrically when the engine is cold starting, then they are simply a thermal mass once the engine is running.https://en.wikipedia.org/wiki/Glowplug