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One for the elekricky department. 27 May 2022 15:44 #235409

  • wee-allis
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I have little old Yanmar tractor that had tel-tale lights for Charge, oil and temp. The globe holders decayed and fell to bits, so I replaced them with LEDs. Oil and Temp work ok but charge light won't come on at all. I have checked and alternator is charging ok as it is.

Now I remember somewhere back in the forum, Pierre or Morris or perhaps someone else had a similar problem and a fix was offered. I can't seem to find that bit so asking for advice please.
Steve.

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One for the elekricky department. 27 May 2022 16:54 #235410

  • hayseed
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Steve, I have a Vague recollection, that you may need to put a resistor in the Circuit.. BISTBC
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One for the elekricky department. 27 May 2022 17:42 #235411

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The bulb may be polarised. Some are, some aren't. (the ones I bought for inside the caravan were; I had to swap the wires). If you swap the wires and it works, you have your answer. Usually the (incandescent) bulb provides a little current to excite the alternator, but if it blows, some revs will usually get the alternator to self-excite on residual magnetism (probably what's happening now). The resistor mentioned is for when the alternator won't self-excite.

Jarrod.

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One for the elekricky department. 27 May 2022 18:14 #235412

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Thanks Jarrod, the terminals are marked + & - and I double checked them. I may have to stop being a tight arse and seek the help of an expert. It's just that I have so much faith in the brains-trust of the forum.

Steve.

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One for the elekricky department. 27 May 2022 20:29 #235413

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The charge light comes on when ignition is on but engine not running and therefore that charge light lights up when the current is running in reverse - so maybe swap the wires to test my dodgy theory. Other thing is that an led may not have a enough resistance to make that circuit work, same as seen in some turn indicator cans that won't drive led lights.

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One for the elekricky department. 27 May 2022 20:52 #235414

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LEDs are polarised so that as mentioned maybe the problem. You will want the positive towards the switch and the negative to the alternator.
For an incandescent bulb you use a 510 ohm resistor in parallel to the bulb, not sure with a LED .
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One for the elekricky department. 27 May 2022 21:27 #235417

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LED globes do not draw enough current to excite the system. Replace that one globe with a standard 2w globe (I think its 2W) and all will be good.
Cheers Cobba & Cobbarette
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One for the elekricky department. 28 May 2022 19:57 #235454

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Thanks for all the hints. It's bloody raining again here, so can't get back to it.

Cobba, can't put a globe in as the reason for the change to LED's was because the globe holders were U/S.
I'll let you know how it turns out, but I'm sure one of the answers on here will be the fix.

Thanks again.
Steve.
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One for the elekricky department. 28 May 2022 20:54 #235473

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Hi Steve, I have read many times that LED lights won't excite the system enough to make it charge. I have not got a clue about adding a resistor in line but it would be worth a try. It would normally need that slight drag of current to kick things off.
I stuck at a pinch then globe holders are readily available new if you have to go back to the old style. Maybe try phoning the local electronic shop or auto electrickery bloke for a definate solution.
Cheers Cobba & Cobbarette
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One for the elekricky department. 29 May 2022 07:05 #235492

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Being a industrial electrician not 100 percent on the topic but my take on it this, the light comes on difference of voltage so when the key is on the light is bright, as the generator winds up the light fads until equal voltage is reached then it is out, if the voltage regulator is set right it will light again as the voltage lifts above battery voltage the light may have a slight glow or maybe not. Once the generator has been run once residual magnetism will excite the generator, but the the LED will not have the current draw for feed back to the regulator so it will not function best thing to do is chuck the LED in the bin.
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