Regulator / rectifier

[Tim Allman]

When measuring voltages everything should be connected properly. The voltage between the RR and the battery when disconnected (or equivalently, 'connected' through the voltmeter) is hard to interpret and would require intimate knowledge of what's inside the RR.

The charging current you measured suggests that everything is healthy. Try measuring the battery voltage with the switch off and with the engine running. You should see values like I mentioned above.

[cadman]

I have done the same thing using a solid state regulator/rectifier off a Kohler twin.

Reading battery voltage before and after the engine is running should tell you if it is charging. A fully charged battery is about 12.6-12.7VDC. With the engine running you need to see more. If you can't get close to 13.5VDC then battery charging is marginal especially if you putt around town.
Try it with the headlight off.

I find usually the Dream alternator does not output enough AC voltage to keep the battery charged unless you you are running at 5000RPM or more and then it is marginal. You can check the alternator by disconnecting the three wires from the alternator and checking what the AC voltage output is. You need at least 30-35AC volts to have any chance of keeping the battery charged.

[GregMcN]

Thanks everyone.
At the moment I am struggling to get the bike running reliably so hard to test anything but will do all the checks/ analysis you have suggested when I can. The bike has only had one run out so far and the battery was in a poor state of charge the next morning but I need to work out why.
I am not sure how good a condition the battery is in as it will only start the engine from cold after it has been fully charged but hard to know if that is battery condition, lack of charging or extra load because I have a 350 conversion of unknown compression ratio.
If I need it are there any higher capacity batteries available that will fit the CB77?

Greg

[DJM]

Greg,

The 350cc kit shouldn't pose any issues with battery capability.

You could go or one of the Lithum ion batteries which offer more cranking amps and amp hour capacity in a smaller case but it shouldn't really be necessary. Check 'carrot Cycles' website for details.

They are expensive and may need a special charger too.

If you get the charging system working properly it shouldn't be necessary, I use Mottobat batteries on my bikes mostly because they are a sealed design but I know plenty of CB72/77 and CB450 owners who use 'old fashioned' lead acid batteries.

Contrary to other peoples experiences I can run either of my bikes all day long with headlights on (and flashing indicators too) and end the journey with a fully charged battery.

I used a CB77 as daily transport back in the 1960s and maintaining a charged battery was never an issue back then (even commuting in winter, and shouldn't be now if everything is in good order.)
You have a new regulator/rectifier already and it sounds as if there is a question mark hanging over your existing battery. I suggest you either borrow a known good battery for your tests or bite the bullet and buy a new one. Any tests you do with a suspect battery will give you suspect results.

[GregMcN]

Thanks Dennis

Based on your positive experience I have ordered a Motobatt battery.

I have also obtained some more measurements. I measured the voltage across the battery whilst the engine was running, this was about 13.5v at idle rising to about 14.8v at increased revs... I guess this suggests the reg/rect is doing its job?

I also measeured the AC voltage of the generator. This showed about 16v between yellow wire and earth, and about 15v for the pink though the combined feed gave a slightly lower voltage at about 13v. These were all at idle so I guess I should have tried increasing the revs but did not get round to that.

[G-Man]

Greg

Your 13.5 to 14.8 v suggest the charging system is working well.

G

Thanks Dennis

Based on your positive experience I have ordered a Motobatt battery.

I have also obtained some more measurements. I measured the voltage across the battery whilst the engine was running, this was about 13.5v at idle rising to about 14.8v at increased revs... I guess this suggests the reg/rect is doing its job?

I also measeured the AC voltage of the generator. This showed about 16v between yellow wire and earth, and about 15v for the pink though the combined feed gave a slightly lower voltage at about 13v. These were all at idle so I guess I should have tried increasing the revs but did not get round to that.

[GregMcN]

Thanks Graham, once I get a new battery then that side of things should be sorted.