4L0 RD350LC Battery Charging Issue

[thylacine]

Hi All,



Battery went flat on last long run on my '81 RD350LC, appears to have stopped charging...was lucky to make it home.

Into the shed, recharged the battery and tested it with volt meter the next day:

- Ignition off 12 - 12.1V
- Ignition on ~10V
- Engine started at (idle to 4000rpm) ~9V


I guess it's either regulator, rotor, stator or wiring issue. Is there any way to test the alternator and/or regulator independently? Does any one component typically give-up first?


All thoughts and feedback appreciated


Cheers

TC

[oldbritguy]

Hi TC and welcome.
These bikes are now 40 years old and most of the electrical components although well made when new may be showing their age a little and getting a bit tired
Charging system is simple and easy to check if you have a workshop manual and a multi meter.
Check readings across the windings on the stator (white wires)and compare with what the manual says.
Rotors are quite robust and relatively trouble free unless they have had a knock.
Regulator/rectifier is the usual suspect but check all the connections on the charging circuit looking for signs of corrosion and not forgetting the earth. Earth wires on these bikes are notorious for the black death and finally check the battery for damage and electrolyte level. If it is getting on consider a replacement.
Let us know what you find. 🙂

[midlifecrisisrd]

Hi TC

Firstly I'd say the battery is knackered but the charging circuit ain't healthy either

Check the 4 pin connector from the genny is ok. They tend to overheat and fry

Haynes manual will give the correct readings for checking the generator output but most likely the regulator or a poor connection

Steve

[stirling11]

Interesting tag you gave yourself

I presume you’re in Tassie ?

And possibly a Richmond fan ?

Agree on the battery being stuffed particularly with that amount of voltage drop

[thylacine]

Hi All,

Thanks for the feedback. Shall give it a once-over and see what i find. Battery a little tired, but something else going on as well.

Not in Tasmania, but not far away in regional Victoria...

Will let you know what I find

Cheers

[4l04ever]

You can measure the stator output on the 3 white wires while the bike is running. You have to measure each combination of 2 of the 3 wires. IE if you label the wires ABC, you need to measure between AB, AC and BC.

Rev the bike to 3 or 4 thousand revs and check each voltage. It should be around 40 to 60 volts AC on each pair. If all 3 outputs are good, you may have a problem with the regulator/rectifier module. If one or more pairs are lower than the others, you need to check your stator.

As mentioned above, the connectors tend to melt on the 3 white wires, as they get bad connections and are trying to deliver a fair amount of current.

[thylacine]

Hi again all,

Had a play over the weekend.
- A/C output seems ok across the three wires - about 40V AC at 3000rpm across each, and continuing to rise steadily with more rpm.
- Electrical connections all look ok, no signs of melting. Gave them a clean anyway.
- Voltage regulator: did the resistance check in both directions per Haynes manual: when it's supposed to have continuity, it's open-circuit, and when it's supposed to be open-circuit, it gives ~5 to 7.5 Mega ohms. I double-checked my polarity on the circuit tester as it seems back to front. Should they have full continuity in one direction when working correctly (ie zero Ohms?).

Sounds like I should get a new regulator on order from Y*mbits.

Cheers

[thylacine]

On related subject of 40-year old electrical modules, has anyone used the replacement CDi units from this company in the US?
www.regulatorrectifier.com/catalog/1980-1982-yamaha-rd350-lc-cdi-unit

There seem to be a few programmable out there, but just looking for something to replace the standard unit.

Cheers

[shaunthe2nd]

I've rebuilt and owned quite a few early LC's and never had a problem with the CDI on them. I have had to replace the odd regulator though.
The 31k CDI is a different story though and they seem to have reliability issues. I've just had to locate a 29k-50 cdi for mine, and on looking around, it seems that those are troublesome.

In answer to your question though, no I haven't used those replacements.
Hope you get sorted.

[4l04ever]

Yambits are probably not the number one choice for spares...

[cb250g5]

Just out of interest, why do you think you were lucky to make it home?

The battery is not part of the standard ignition on these bikes, or were you riding at night and worried that you would run out of headlight?

Oh, BTW, don't buy from shambits.