Author Topic: Rd125 charging issue  (Read 373 times)

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Offline Qweest

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Rd125 charging issue
« on: December 01, 2019, 06:52:14 PM »
Hi lads
I have rd125dx which used to run perfectly without any issue however recently it started to really put my nerves on the limit. Problem looks like this, I have good voltage on idle and 5k from 14-16v which is fine however on idle with lights on it would drain fully charged battery within 10min. Checked all grounds and wiring and also amps which looks looks like this:
Ignition on 0.5amp draw
Ignition and coils 4.5 amps draw
Running on idle lights off  2amps draw
Running idle with lights on 7 amps draw
5k rpm with lights on 1amp charge
It means it would drain battery on idle even with lights off it would drain the battery and I can't find where the problem is I even replaced stator for used one I had in garage but it is same so I changed rectifier for solid state rectifier but all looks same just bit bigger voltage. Does anyone got an idea why it drains soo much or why it doesn't charge with good current thanks

Online Johncb500

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Re: Rd125 charging issue
« Reply #1 on: December 01, 2019, 07:21:28 PM »
Check the headlamp wattage.
35w should be about 3amp.plus ignition. Tail and other bulbs could add another couple of amps.
Remember. The generator on all 70's bikes are marginal.
No one ran headlight in daylight.

But. With these little things 5k is nothing when riding

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Online Barnett

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Re: Rd125 charging issue
« Reply #2 on: December 02, 2019, 09:20:21 AM »
Yes thats quit a draw at idle. Charging usually begins at about 2000 rpm but it may vary from this a bit so charging at idle is poor if anything. Its a crude but simple system which relys heavily on good battery health. Battery gets quite a hard time and its vital it is topped up, healthy with good connections. The rotor is a perminant magnet type I believe and due to age may not be as powerful as it was when new.
Have you checked stator coil resistance?
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Kawasaki 1977 z650 B1 on road
Yamaha 1972/3 U.S. early RD350 ongoing project.

Offline Motty

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Re: Rd125 charging issue
« Reply #3 on: December 02, 2019, 07:06:54 PM »
I am assuming there is a short somewhere, I would tackle it by disconnecting the electrical parts one by one. Painful and time consuming but one of our technical gurus may be along shortly

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Offline ajh

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Re: Rd125 charging issue
« Reply #4 on: December 02, 2019, 08:51:30 PM »
sure your battery is ok?
in West London

77 RD250d, 80 DT175mx

Offline Qweest

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Re: Rd125 charging issue
« Reply #5 on: December 03, 2019, 02:38:41 PM »
Right everything is strip including wiring and indeed there is some short somewhere I found out that mounting bolts from coils got resistance to 12v and condenser wires. Are those mounting bolts should have any connection to coil? Might that's where short is. According to manual there isn't any grounding? I check everything and all leads to coils however I don't want to spend money before I'm sure also are there any coil alternatives I heard that old Kawasaki coils could fit

Offline ajh

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Re: Rd125 charging issue
« Reply #6 on: December 03, 2019, 04:54:07 PM »
take this with a pinch of salt, I dont know if this will work on lower powered electrics or whether its relevant to your issue but I've done this in the past to identify shorts/faults

If something is drawing significant current off the battery, then it'll likely cause a spark when you connect disconnect one of the the battery terminals. you can try disconnecting/switching off various components until it no long arcs/sparks when you connect disconnect battery.
in West London

77 RD250d, 80 DT175mx

Online Johncb500

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Re: Rd125 charging issue
« Reply #7 on: December 03, 2019, 04:59:43 PM »
Right everything is strip including wiring and indeed there is some short somewhere I found out that mounting bolts from coils got resistance to 12v and condenser wires. Are those mounting bolts should have any connection to coil? Might that's where short is. According to manual there isn't any grounding? I check everything and all leads to coils however I don't want to spend money before I'm sure also are there any coil alternatives I heard that old Kawasaki coils could fit
The coils should earth.the plug lead is part of the circuit.
The 2 12v leads should not earth. As the points act as the earth.
Have you got a multi meter?



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Offline Numbskull

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Re: Rd125 charging issue
« Reply #8 on: December 05, 2019, 01:59:46 AM »
Be sure the brake lamp is not on all of the time.

Rob
The lyf so short, the craft so longe to lerne.

Offline Qweest

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Re: Rd125 charging issue
« Reply #9 on: December 08, 2019, 06:49:24 PM »
Right all sorted it's charging at 2k so all good now it was bad earth and 65 watt bulb however the original misfire which led me to charging issue is still here but will write another post because after 20h in the garage I'm out of ideas. Thanks all

Offline Gr8uncleal

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Re: Rd125 charging issue
« Reply #10 on: December 08, 2019, 06:52:32 PM »
Good news.