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Discussion Starter · #1 ·
Hi Folks, I have replaced my original rectifier on my 74 Honda CB125s with a regulator rectifier so I can use it with an AGM battery. I put a multimeter to it and after revving the engine I'm getting a reading of about 9.5 Volts. Is this a normal reading in your experience with 6V systems?
 

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That would be about right I'm thinking. Might even be high but I'm assuming the bike was running when you took the reading. If you were reading 6v that battery would be shot.
 
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Discussion Starter · #3 ·
Yes the bike was warmed up and running when I took the reading. The bike never had a regulator before, just a recitifier and I stuck in an AGM battery. It ran for a couple of weeks then died and blew out my light bulbs. I just got this regulator rectifier from amazon I'm hoping it will do the job but initially I was thinking the 9.5 volts was high as well so just wanted to validate.
 

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Well I'm not guaranteeing it isn't too high. 6v is so ancient history that I'm not sure either but with it running it will be higher. If a 12v is okay at almost 15v would a 6v be okay at 9.5v? Seems it should but I'm a little surprised our electrical gurus haven't corrected me if I'm wrong. Give them a bit more time. They may pop in yet.
 

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9.5 seems quite high to me, I'd expect more like 7.5 and no more than 8.5V. Did you measure with the lights on and a good battery in place?

Amazon kinda sucks when it comes to component specs. The device specs should be quite a bit more than the size of box it gets shipped in. We should be able to see power handling capacity and regulated voltage with an allowed tolerance range. If they tell you nothing, how can you say it's out of spec?

I am not a fan of spending the extra money on high tech batteries for vintage bikes, because the charging systems are so crude.
 

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I noticed that the list of applications that were for the device you purchased, didn't include the 125, but was primarily a list of larger machines. That device, by the way, is apparently a RECTIFIER / regulator. It's probably just a Zener diode tacked onto a bridge rectifier. Back in those days, I bet that Honda was still using Selenium rectifiers, which have higher internal resistance, hence higher voltage drop. Using silicon diodes in modern rectifiers means something like 1.5 volts less drop in the rectifier than would have been seen with the old selenium rectifier. If you can measure the charging CURRENT into the battery, instead of the voltage, and it's not more than 1/8 of the ampere hour rating of the battery, then I'd say you should be good even with the higher voltage. If it's higher, you could reduce the charging current by adding some resistance, or adding an external Zener diode to drop the voltage to a safer level.

Did you measure that 9.5V with the lights on or off, and was a good battery in the system when you measured? I ask because the voltage over a crappy battery will be higher, their internal resistance generally increases as they go bad. Also, did you measure any other reference voltages, to verify that your meter is accurate? For example, a pair of fresh alkaline flashlight batteries in series should give you 3.0 to 3.1 volts.

Here's a good reference on lead acid batteries: https://www.itacanet.org/eng/elec/battery/battery.pdf
 

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Yes the bike was warmed up and running when I took the reading. The bike never had a regulator before, just a recitifier and I stuck in an AGM battery. It ran for a couple of weeks then died and blew out my light bulbs. I just got this regulator rectifier from amazon I'm hoping it will do the job but initially I was thinking the 9.5 volts was high as well so just wanted to validate.
Because it did not have a regulator we know that it was originally a "balanced system" type of charging system.
I don't know how a person could convert it to the more modern rec/reg system, but it is interesting to think about.
With it blowing out light bulbs you can be pretty sure that 9.5 volts is too much for your 6 V system to handle.
I'd guess about 6.7 volts up to about 7 volts max is where you would want to be. Just guessing though.
The old 6 V balanced systems were before my time for the most part. I would go back to the original battery, but that's just lazy old me.
Looks like johnnyvee might have some good ideas so........
........ You're up johnnyvee :)

S F
 

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I was thinking 9.5 was a bit much. However it may depend on the amps. Above it was said that 12 volt batteries charge at a max of 14.5 volts. In a cage that is often around 45 amps. With solar panels the volts can go to 17.5, but the amps are only around 5 to 10. So there needs to be a conversion to watts. Amps X volts. If you are blowing bulbs there is too many watts. The old DT175 dirt bikes, would blew the headlight if the tail light was busted. Usually from an endo. So the bulbs can only take so much zap, and you appear to have too much. Without changing your current system, you could put in a wattage drain. A larger bulb might do it. Or in radio talk a dummy load. They used to use aluminium heat sinks, but I forgot how they worked.
JV seems to have a grasp of the electrical stuff, so too Semi. And finally, some of the cheap stuff from China can be a bit rough around the edges. My new thermometer is reading 20 when it is 48.

UK
 

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Yeah, I was afraid that might be a little excessive on the voltage.
Glad the gurus finally showed up. Way to go guys.(y) (y) (y)
 

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Discussion Starter · #11 ·
Update: I have replace the AGM with another AGM thinking it may be damaged. So now with the new Regulator Rectifier and new AGM it’s holding around 8.5v now revving and 6.2v w high beams revving. Funny on the same bulb low beam is blown out but hi-beam still works.

I'm going to observe how the bike behaves with this but I may take SemiFast's advice and go back to the old Yusa acid battery.
 

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Yeah no specs! Any recommendations on who has a 6v regulator rectifier that’s not $120?
this is what I read: is there a way to check it?
Something doesn't add up with the Amazon description for that part. If you look in the Product Description section down under Specs. at the list of bikes that it is supposed to fit, it's showing mostly 450s and 350s. All of those are 12V system machines. The only bike I see on the list that I think is 6V is the XL175. None of the 125s and 100s that are listed in the Item title are shown in that applications list.

This makes me wonder if it isn't indeed a 12V regulator. Even if Amazon sellers care, ( which most of them don't, they just want your money), in my opinion, the vast majority of them don't know anything about what they are selling.

How you would test something like this, because it's a combination Rectifier and Regulator would be to hook it up to a variable AC input, and put a load resistor on the output and voltmeter on the output. Variable AC could be cobbled together with a light dimmer and a control transformer from a furnace. Those are 24VAC output, 110V input. The transformer won't like the chopped AC out of the dimmer, and will heat up with hysteresis current, so keep the test short. For a load resistor should be something like a 50 ohm, 5 watt should do the job. Put the AC in and see what DC voltage comes out. The DC voltage should rise proportional to the AC until the regulation point is reached, then it won't increase any more.

Perhaps you could use a regulator from an old vintage bike. British bikes used 6V systems later than the Jap bikes did.

Something like this MIGHT work, but it would take more research to know how to wire it: Royal Enfield Bullet Electronic Rectifier 6v Positive Ground | eBay This device is positive ground, so it would have to be isolated from the frame if your machine is negative ground. These regulators are nothing more than a zener diode in a heat sink. When the threshold voltage is reached, they dump excess power to ground, dissipating the resulting heat.

I would consider continuing to use the original system, as it was designed. The battery itself acts as a sort of regulator in a crude charging system like that bike has. The charging system is designed to be incapable of producing enough power to seriously overcharge the battery in normal use. Unfortunately, the more expensive AGM battery may be less capable of taking the abuse than the older tech. wet cell. Once the battery goes high resistance, system voltage goes up and the light bulbs blow out, like you experienced.

In my opinion, there's no getting around the need for maintenance and knowledge when one rides a vintage machine like yours. Good Luck and have fun!
 

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Hi Folks, I have replaced my original rectifier on my 74 Honda CB125s with a regulator rectifier so I can use it with an AGM battery. I put a multimeter to it and after revving the engine I'm getting a reading of about 9.5 Volts. Is this a normal reading in your experience with 6V systems?
Hi Folks, I have replaced my original rectifier on my 74 Honda CB125s with a regulator rectifier so I can use it with an AGM battery. I put a multimeter to it and after revving the engine I'm getting a reading of about 9.5 Volts. Is this a normal reading in your experience with 6V systems?
Please note following points
1) Use multimeter of good brand ( FLUKE) which are calibrated also frequent calibration is not required
2) 6 Volt System Voltage should not exceed 7.5 Volts while charging
3) In vintage 6 Volt system machines following systems are used to control charging
a) ZENAR DIODES ( 1966 Triumph Daytona ) ALTONATOR
b) Cut Out / Regulator Box which has coils and points for DC GENERATOR
( 1956 BSA GOLDEN FLASH)
C) Light Switch Control where head light switch selects the alternator coils
are selected as per lighting load to charge.
( ROYAL ENFIELD BULLET 1962 )

4) AGM battery life will be reduced if charging voltage / current exceeds the
specific values of battery model
Please check which charging system is used on your machine
 
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