Author Topic: Charging System Specification  (Read 3124 times)

Offline philward

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Charging System Specification
« on: February 16, 2022, 02:37:02 PM »
I'm currently converting back to electric staeter on the CR750 Replica.
For authenticity (as near as you can expect for a road going replica) I used a race alternator that was narrower than standard in conjunction with a narrower cover. This allowed me to use a nearer to original fairing without cutting a hole in the fairing for the alternator. Down side was that the kit junked the starter ring/clutch (hence no starter motor)
the Electrex World race alternator kit included a voltage regulator/rectifier that I have mounted under the seat with the battery and all other electrics (the inclusion of the replica central alloy oil tank creates space issues). I want to retain this reg/rec (if possible) as I've squeezed it into position and don't want to re-position/make new brackets.
BEAR WITH ME, I'M GETTING THERE!
The Electrex race alternator I'm told (by Andy at 'GoodBits' who sold me the system), that the alternator only kicks in to charge at 3000 rpm. Not an issue while racing.
Question for the electricery experts, is it the reg/rec that controls when the alternator starts charging or the race alternator.
I need to know this so that when I put the original alternator back on, the system charges as per the original Honda spec - as I can't/don't want to always ride the bike constantly above 3000 revs. It hasn't mattered to date as the battery doesn't get taxed as much without the electric starter motor
Pending the answer, I will be able to retain the rec/reg that on the bike or change it to one thats made for standard 750.
Here's the Electrex race alternator spec
https://www.electrexworld.co.uk/acatalog/RPK-1750-Honda-CB750-SOHC-Alternator-System.html
Thanks in advance
PS, I have found a high cranking amp battery that will fit in the current custom battery box under the seat
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline Oddjob

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Re: Charging System Specification
« Reply #1 on: February 16, 2022, 02:45:34 PM »
The alternator controls when it starts charging Phil, the reg/rec does the converting the AC to DC and the switching on/off of the power coming from the alternator when the voltage gets too high, does this by switching some to an earth IIRC.
Kids in a the back seat cause accidents.
Accidents in the back seat cause kids.

Offline philward

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Re: Charging System Specification
« Reply #2 on: February 16, 2022, 03:12:54 PM »
That was my understanding Ken, so is the current regulator switching the charge to the battery starting at 3000 rpm or is the race alternator not producing any charge until 3000 rpm?

Sent from my moto g(50) using Tapatalk

Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline Bryanj

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Re: Charging System Specification
« Reply #3 on: February 16, 2022, 03:29:24 PM »
The answer is both, the generator needs to produce over battery voltage to charge and this depends on speed, number of windings and input to field coil
Reg controls input to field coil, best to ask supplier if it will work on a standard system
A standard system with lights on doesnt charge till over 2500rpm!

Offline Oddjob

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Re: Charging System Specification
« Reply #4 on: February 16, 2022, 03:42:53 PM »
What about without lights on Bryan? Never really got involved with electrics but I worked on quite a few problems back then so maybe I've just forgotten as I got older.
Kids in a the back seat cause accidents.
Accidents in the back seat cause kids.

Offline Bryanj

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Re: Charging System Specification
« Reply #5 on: February 16, 2022, 04:20:15 PM »
Memory has gone Ken but there is a charging test page in the manual with loads and revs etc

Offline Lobo

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Re: Charging System Specification
« Reply #6 on: February 16, 2022, 10:28:57 PM »
Phil, dunno if this helps you… but it helped me!
Simon

Offline Lobo

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Re: Charging System Specification
« Reply #7 on: February 16, 2022, 10:31:33 PM »
…but wait… there’s more!

Offline philward

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Re: Charging System Specification
« Reply #8 on: February 17, 2022, 09:11:48 AM »
Thanks Simon

Sent from my moto g(50) using Tapatalk

Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Online K2-K6

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Re: Charging System Specification
« Reply #9 on: February 17, 2022, 09:54:18 AM »
The honda manual output chart shows 12.4 volts at 2000rpm (just about reaching parity with a reasonable battery) which could be interpreted as "switch on point" as the rpm is producing output that can charge a low battery.

Specifies 14.5 volts @ 4000rpm to reach full output.

Also 13.2 volts @ 3000rpm, not a huge amount over a decent battery.

You can see the gradient from that, and why low rpm accompanying high draw would leave the battery depleted.

Offline philward

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Re: Charging System Specification
« Reply #10 on: February 17, 2022, 11:40:29 AM »
I've seen that graduation from the manual and it seems that if the race alternator and its rec/reg isn't that much difference. So, keeping the rec/reg from that system when I convert back to standard alternator should be ok.
Andy at 'Good Bits' has developed a race alternator cover that accomadates the stator in the cover (as opposed to bolting on to were the starter gear fits on the Electrex system) but due to the cost including the Electrex system is over £1000 he's hesitating to produce me a cover (about £320 to me as I have the Electrex system already). This would allow the starter to be installed and retain the narrow profile of the race alternator.
Based on the race alternator appearing to have similar characteristics to the standard system, (Electrex spec sheet says output is 25 amps - IS THAT SUFFICIENT?). I might push Andy to make me a cover as a one off.
« Last Edit: February 17, 2022, 12:42:59 PM by philward »
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline Sesman

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Re: Charging System Specification
« Reply #11 on: February 17, 2022, 11:43:34 AM »
25A = circa 300W. Should be enough I would have thought?

Online K2-K6

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Re: Charging System Specification
« Reply #12 on: February 17, 2022, 11:58:23 AM »
I think it was Andy I was chatting to at the last DS open day. He had his circuit race 750 there and trouble to get it firing so we could hear it, got it in the end though and sounded good.

Offline philward

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Re: Charging System Specification
« Reply #13 on: February 17, 2022, 12:54:07 PM »
K2 - K6 , here's mine shortly after initial start up  - has baffles fitted and before Smiths sorted calibration of rev counter. Made few mods since.

https://www.youtube.com/watch?v=YmL8YYWeUMo

PS, if you look at the digital speedo, you can see the charging voltage (bear in mind that the rev counter is reading 1000 rpm too much at the time)
« Last Edit: February 17, 2022, 12:58:35 PM by philward »
Current Bikes:-
Honda CB750K2 (1975)
Honda CB500K2 (12/1972)
Honda CR750 Replica (1972)
Honda CB350K0 (1969)
Kawasaki ZZR1100D3 (1995)
Kawasaki ZZR250 (1990) Project (Going on eBay ASAP)

Offline Oddjob

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Re: Charging System Specification
« Reply #14 on: February 17, 2022, 03:38:51 PM »
IIRC Phil the standard system only pushes out 200w. So if the Electrex system pushes out 300w that's a big improvement.
Kids in a the back seat cause accidents.
Accidents in the back seat cause kids.

 

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