Overheating rectifier - solutions?

[Seanny]

Previously I got a new battery and the scooter starts fine. After about 3 weeks of riding the battery starts to act weak and couldn't start again. I brought the bike to a mechanic to see if there's a charging issue. The mechanic did a test and said the battery is charging, but the rectifier is very hot. He suggests getting a new rectifier.

I am going to buy a new rectifier any one know where to find parts for the Downtown 300i including the rectifier? Any 3rd party ones that wouldn't overheat as easily as the OEM one?

Also are there any tips on keeping the rectifier cool? What are some causes of why the rectifier overheats?

[CROSSBOLT]

Regulator-rectifiers on this and other models are of the "shorting" type and tend to run pretty warm in  normal use that's why the generous fins. The Kymco part is nearly identical to the similar Honda part and even has the same basic part number, 31600! You can find these on ebay and Amazon for 12 to 25 bucks. Kymco wants a lot of money and your first-born child! I do not understand the weak battery but the tech says it is charging. Does not seem to fit.

[Seanny]

Regulator-rectifiers on this and other models are of the "shorting" type and tend to run pretty warm in  normal use that's why the generous fins. The Kymco part is nearly identical to the similar Honda part and even has the same basic part number, 31600! You can find these on ebay and Amazon for 12 to 25 bucks. Kymco wants a lot of money and your first-born child! I do not understand the weak battery but the tech says it is charging. Does not seem to fit.

Hi CROSSBOLT, I don't understand as well. It's already weird that a new battery is dying after just 3 weeks of riding. I ride almost everyday to work as well, so I have no idea. But I was able to start the bike with the weak battery by using a USB battery jump starter.

I rode it to a mechanic to let them test if there's a charging problem. They said the battery is charging but the rectifier is very hot and recommended me to change the rectifier but they just don't know where to get one.

Do you have any other idea as to why a new battery started dying that quickly? I changed all the fuses as well, there's no warming grip I took that off. Either there's a power leakage somewhere or the rectifier has some problems but I'm not sure if there are other possibilities.

[CROSSBOLT]

New battery goes flat while riding means it is not being charged. Period. Now, WHY is in the ballpark of your tech. And he failed. Like I said, the rectifier-regulator runs pretty warm. How warm or how hot I do not know but all of mine so far have not failed, that is batteries were always able to start the machines except when they got old or failed. Once replaced then everything went back to normal. Your tech needs to show you what he did to say the battery was being charged. Bet he can't do that. Get another opinion or get out your multimeter and let's find the cause. It will be: 1. A bad connection, 2. Bad regulator-rectifier or 3. Bad stator. This is assuming the new battery is not defective so take it out, charge it and then take it somewhere that does batteries and get it load tested. Eliminate that as a cause right up front.

[Seanny]

New battery goes flat while riding means it is not being charged. Period. Now, WHY is in the ballpark of your tech. And he failed. Like I said, the rectifier-regulator runs pretty warm. How warm or how hot I do not know but all of mine so far have not failed, that is batteries were always able to start the machines except when they got old or failed. Once replaced then everything went back to normal. Your tech needs to show you what he did to say the battery was being charged. Bet he can't do that. Get another opinion or get out your multimeter and let's find the cause. It will be: 1. A bad connection, 2. Bad regulator-rectifier or 3. Bad stator. This is assuming the new battery is not defective so take it out, charge it and then take it somewhere that does batteries and get it load tested. Eliminate that as a cause right up front.

They are not a Kymco dealer, but a dealer of another major brand, so they are not very familiar with Kymco I think.

I have a multimeter but it's nothing professional, just a household one in case if I need it. I am not sure how to test and find out if there's a problem with the rectifier vs bad connection problem or other possibilities. Do I need to take out the fairings (or covers of the Downtown 300i) to do that?

[CROSSBOLT]

Your multimeter will do fine. First do the battery charge and test, please. Then once we know about that we can focus elsewhere.

[scooterfan]

How old is this scooter ? Maybe you should also look for corroded terminals, or a bad earth connection.

If the battery Voltage gets lower by time,  the rectifier will work harder and it will get hot anyway.
Maybe you should also check the rectifier's heat when the battery is still almost fully charged. The heat should not be as high as when the battery voltage is much lower.

[Seanny]

Just got the bike back, how should I test if the battery is being charged?

Should I measure the voltage before turning the bike on, after turning the bike on, and then letting the bike run for awhile, revving the bike to around 5000 rpm and then measure again?

How old is this scooter ? Maybe you should also look for corroded terminals, or a bad earth connection.

If the battery Voltage gets lower by time,  the rectifier will work harder and it will get hot anyway.
Maybe you should also check the rectifier's heat when the battery is still almost fully charged. The heat should not be as high as when the battery voltage is much lower.

It's a 2011, so not super old, but also very possible for corrosion. I also know the previous owner parked it outdoor and hasn't ridden it for awhile before selling it to me.
The mechanic said the battery is charging, but when the bike is running and revving the rectifier gets really hot to the point where you just can't touch or hold it, and as it's temperature rises, the charging capability decreases.

I only know the + and - terminals that are connecting to the battery, are there other major terminals that I can check and see if they are corroded?

[scooterfan]

Just got the bike back, how should I test if the battery is being charged?

Should I measure the voltage before turning the bike on, after turning the bike on, and then letting the bike run for awhile, revving the bike to around 5000 rpm and then measure again?

It would make sense to get a voltage reading right now, without running the engine. Then get another voltage reading after about another 50 miles or so, while the engine is not running.
I think it would make sense to somehow compare the rectifier's heat while the battery's voltage is going "downhill".
If the rectifier's heat get worse while the battery's voltage is going down, I think the problem would be elsewhere - not at the rectifier.
But obviously - rectifiers are quite cheap, and an "easy way out" might just be to get a new rectifier.

 

[mousejunks]

The rectifier always gets hot.

Check my guide on how to test the battery and charging system.

[Seanny]

The rectifier always gets hot.

Check my guide on how to test the battery and charging system.

Yeah I was following our guide as well I talked about it on another thread. Unfortunately my leads that came with my multimeter are too short and couldn't reach the harness and touch the metal inside that. I will buy a set of new leads and hopefully that would solve that problem and follow your guide.

On the other hand, I did a test on the battery and here are the results:
Battery voltage when bike is not on: 12.54V
When I turn the keys on but didn't start the bike: 12.0xV
When bike just started: It jumped really quickly from 11.xxV to 10.xxV and then back up to idle voltage

When bike is on and idle: 14.18V
When I rev it to ~4000RPM: 14.2x-14.3xV

[mousejunks]

Those voltages actually sound good. If starting issues remain you can check for corrosion on the starter motor terminal and the spark plug cap.

[Szpilu]

Those voltages actually sound good. If starting issues remain you can check for corrosion on the starter motor terminal and the spark plug cap.

Hi. I changed the rectifier last weekend a new one. When the engine running the Voltage is 14,2V on the rectifier. And when I use the head lights and the rpm is 4-5000, 14,5V.


on the ebay there a new designed rectifier from the Kymco.

Link:https://www.ebay.com/itm/ENC-Regulator-Rectifier-REG-REC-COMP-ORIGINAL-KYMCO-31600-KED9-910-Xciting-250/291799405858