Battery flattening

[Jello]

I noticed this happening a few months ago but didn't do anything about it. A kick start bike allowed me to neglect it this long.

My battery loses charge so that I achieve no lights at all with the engine not running. Charging the battery usually gives me lights for about a day, however by the time I next ride it (usually the next day) it's flat again.

I can achieve lights with the engine running, so I can assume the generator is sound.

Your first thoughts might be regulator/rectifier. I have suspicions that could quite easily not be the case, though. When I bought the bike, the previous owner handed me a box of odds and sods of parts he has changed over the period he owned it. In it were included 2 reg/rec units. Obviously he attempted to fix the issue by replacing them. Without success.

Is there a way I can test the reg/rec unit currently fitted to rule it out?
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Honda MTX 125

[Itchy]

Multimeter across the terminals of the battery should not read more than 14v while revving the bike if it does the reg / rec might be fried but check the connectors first as sometimes the block connectors corrode...


Doesn't matter anyway as you have the kicker, and its not a good idea to use the lights on with the battery only anyway as it will kill your battery pretty sharpish.... hah here was me riding in the dark 80mph running total loss as the reg/rec had died.... took lights on I'd have been stuck outside warrington lights off I managed to limp to bolton.


Oh and if the reg / rec was replaced with a Honda one you have exactly the same problem again , I have a Kawasaki one on my Africa twin , it needs air flow and also needs to be cushioned from vibrations which means rubber mounts to the frame.

Ride around for a bit then feel the reg/rec if you burn yourself then this is very bad, it should get mildly warm if working correctly.
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Spain 2008France 2007Big one 2009 We all die. The goal isn't to live forever, the goal is to create something that will. In the end, your life will flash before your eyes. Make sure it is worth watching.

[lonner]

you need a multimeter to check volt's .


connect to the battery and if its working you should see 13.5-14.7 volts with the engine running

check all connections for rust etc and earth's are sound hth

if you don't have a metre the lights will brighten slightly when you rev the bike and shows its charging

the battery may be shot and unable to hold a charge if its a couple of years old or a cheap nasty thing as some last 12 mths and will flatten very quickly

[Jello]

I forgot to mention; the battery is new, only a few weeks old. It suffers the same problem as the old one.
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Honda MTX 125

[Gawain]

[Jello]

[The Disapproving Brit]

I doubt it. Longer rides will increase battery life, and even a 2 mile commute should give you a week or so even without any charging, since you're really only using it for the starter.

I have a similar issue, but I know I have a short somewhere - I just need to find time to strip the bike down to find the bloody thing.
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Current Bikes: 1983 Honda VF400FD / 2003 Honda VT750 Shadow
Bike Test Passed 18/03/09, Car Test Passed 14/05/13

[Jello]

[Gawain]

[Jello]

I'm looking for a way of checking if the reg/rec unit is functioning correctly.

Any help appreciated.
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Honda MTX 125

[Gawain]

Easy, disconnect the positive and negative leads that lead from the reg/rec to the battery (may be directly earthed to frame). Then run the bike with a multimeter connected. Idle voltage should be 13v or so, when reved volts should stay below 15v but above 14v. If the readings are right the alternator and reg/rec are fine, if not then one is causing problems. You can check the alternator by checking continuety with ground from alternator leads, should be no continuety. And by checking ohms between alternator wires, should be similar between all 3. You can also test ac output from the alt output wires.

[Finglonga]

As already said put a multi meter across the battery with the engine running and you will tell if the rectifier is shot.

Remember though the longer you leave it the more chance of killing your new battery.
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Andy Sez....
F.Y.Y.F.F.

[Stelmer]

Reg Recs can go bad many, many ways.

Wemoto guide:

https://shop.wemoto.com/info.dyn?title=Regulator/Rectifier

https://shop.wemoto.com/info.dyn?title=Battery_Care_Guide

If you can turn the lights off and on then the voltage should be a steady 13 odd volts when the lights are off and rise to 14 odd with the lights on at around 4000rpm.

I'd also be inclined to check the ground by doing a voltage test with the -ve wire attached to some metal part of the bike.

Bad connections in the reg reg loom can cause a low charging voltage as well as internal faults. The one on my GSX was not charging much above 13v because someone had butchered one on the loom using spade crimps and fed a wire to the live side of the brakelight switch to turn it on.

New proper crimps fitted and it now works spot on.

[Bikeless]

When my mate bought his R1,he had electrical problems,we spent days on it,bought 2 new rectifiers,had a battery amperage check and checked all the loom.

The fault was somebody had removed a main earth wire from the starter to the battery and replaced it with a small wire from the battery to the gearchange cover.

We only noticed after checking my bike.

[Bikeless]

When my mate bought his R1,he had electrical problems,we spent days on it,bought 2 new rectifiers,had a battery amperage check and checked all the loom.

The fault was somebody had removed a main earth wire from the starter to the battery and replaced it with a small wire from the battery to the gearchange cover.

We only noticed after checking my bike.

[killingtime88]

Hi there funny old world we have exactly the same problem here.
What we have found out today is that the MTX has a strange electric system there are three coils in the Alternator .
1st feeds the CDI unit only
2nd charges the battery through a regulator rectifier unit ,and in turn powers the horn,side lamps and indicators
3rd powers the main headlamp full and dipped beam.This also has what looks like a regulator in circuit between positive and negative
this is why the bikes can run without a battery and the main headlight doesn't work until the engine is running.
I have downloaded a copy of the original manual if you would like it the only trouble it is in french but with a little help from bablefish i am working through it.
if you have a multimeter you can do a quick test start up the bike and connect the multimeter to the two wires coming into the(2 pin plug) at the regulator rectifier you should see an ac voltage up to about 80V.
if this is present check between the green and red wires coming out of the unit(3 pin plug) you should see between 10V at tickover and 18V at 6000 rpm.
You should always charge up your battery before measuring the output from the reg/rec as a very flat /knackered battery can drag the voltage reading down.
Anyway good luck and i will let you know how we get on with this one.
Regards Paul

[killingtime88]

It turns out the 2 yellow wires from the mtx stator were shorted to earth/frame.
we have fixed this by replacing the mtx stator with one from an mbx125 this had the same cdi winding plus normal 3 wire charging system found on most bikes.
both the 2 wire ac lighting regulator and the 5 wire charging regulator have been removed and replaced with an mbx125 6 wire regulator.
the wires from the mtx two wire regulator can just be taped up as all regulation is now done by the mbx reg.
There is one side effect which we can live with and that is the headlamp now works at all times even without the ignition on.
anyway problem fixed.
And of course the headlamp is now fed with dc instead of ac this could have implications down the line with the headlamp switch if it is only ac rated.
Regards Paul