Topic: Charging system not keeping up, blowing fuse

[Dunk]

6 years and 6000 miles after restoration of my CB750 K1 I'm having charging system issues again, which I've had on and off over the years. The bike has a Dyna S, 5 ohm Dyna coils (used to have 3 ohm, changed to lessen amp draw), Cibie headlight reflector with 55/60 watt bulb direct wired from battery through it's own fuse and relays, reproduction main harness, Oregon Motorcycle Parts regulator and rectifier, new bullet connectors on any worn connectors during restoration, LED gauge and indicator lights.

Originally it kept up with all this plus the 3 ohm coils, probably running full tilt all the time but I never had a dead battery. I never use the electric starter so that probably helps. Lately I've noticed gauge lights dimming at idle and battery voltage low when checking, so I put it on the trickle charger regularly. At the end of a 70-90 mile ride at night with headlight on the lights will dim at idle, brightening to normal at 2500-3000 RPM. Riding a bit a gear lower than normal helped recover from this, but it had stalled a couple times from low voltage when coming to a stop.

I cleaned all connections between alternator and battery, the field coil bullet connectors and one of the stator coil connectors were loose so I tightened them. Field and stator coil measured in the correct ballpark. I charged the battery and it read 12.6v after sitting for about 30 mins. Checking voltage while running I found it was charging by about 1500 RPM, better than the 2500+ previously judging by gauge light brightness. I had been riding with light off when stopped during the day or not anywhere I felt I needed the extra visibility of a headlight, but decided to ride with headlight on and measure battery after each ride to see if it kept up to a full load after cleaning and tightening connections.

After a ride the other day, I checked voltage before heading to work today, 12.4x volts. After my ~17 mile ride I had a higher RPM blast on the last stretch to work and the bike died slowing to turn into the lot. Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder. Tightened that up and stole the fuse from the headlight. I got a new fuse holder I'll install, and I saw a reproduction alternator harness is now available from 4into1 that I'll try.

I'll replace the battery, a sealed AGM, as I don't recall if that is 6 years old or 4 years old but it may be best to eliminate it as a factor. Could it be as simple as an old weak battery?

I was thinking the wires in the charging system are pretty small. Even without the headlight load it blew the main fuse today. Might it be helpful to run a larger charge wire directly to the battery? Has anyone done this and how did you do it?

How many amps do coils or the Dyna S pull? Might it be helpful to run the coils and/or Dyna off a relay with larger dedicated wiring?

I picked up a 35/35 watt headlight I could try. Surely it'll be a lot better than the original sealed beam with the Cibie reflector but it would be nice to keep the higher output headlight as I've gotten used to modern lighting.

I also have a CB750A field coil I was planning to try eventually. They had slightly higher output alternators. The A stator measures the same as every K stator I have, but the field coil is definitely different. There was a guy here, up in NH, making higher output alternators and I messaged him to get on the list for the next run but never heard back. Any other high output alternator options?

Any thoughts on my charging problem?

[bryanj]

Sounds like battery failing to me, fuse just a coincidence or battery shorting internaly.
Noal system does not charge till 3000 with lights on and no mattery what reg rec you fit it cant improve on that

[maxheadflow]

According to the wiring diagrams in the manual, the alternator feeds the battery on the battery side of the fuse. This means that the alternator can't blow the fuse.  Your fuse connections are ohmic and the heat is killing the fuse.

You have a weak charging system.  The spec say 210 watts at 12 volts at 5000 RPM. You need to measure the current and voltage at the battery to determine what is going on at say idle, 3000 and 5000 rpm. 

[RAFster122s]

Is it Anders that does the 750 charging system upgrade.  Check back with him to see if he missed your message.
But, unless the battery is just approaching the end of life, you need to address the problem you are seeing.

[scottly]

Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder.

The fuse holder had a poor connection, which caused both the burning and your charging problem.

[tlbranth]

Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder.

The fuse holder had a poor connection, which caused both the burning and your charging problem.

This seems the most likely. Don't just chuck money at it without actually determining the problem first. I'd take the battery to NAPA and get it load tested. If that's OK, I'd put an automotive ammeter temporarily in line with the fuse to see what your actual draw is. I chucked my original fuse holder and installed a blade-type arrangement. I think it works better than the original.

[scottly]

Hey Terry! How are you and your wife? Oops, back on topic; I wouldn't bother with having the battery load tested. I would jump straight to measuring the voltage drop from the battery + terminal to the regulator black terminal with the key on, not running; a poor connection at the main fuse would show a larger voltage. Dunk mentioned a "mini" fuse holder, which I suspect may be a mini blade size? I think Hondaman has seen problems with these? 

[maxheadflow]

Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder.

The fuse holder had a poor connection, which caused both the burning and your charging problem.

Look at the wiring diagram.  Alternator output and battery are on the same side of the fuse.

[scottly]

Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder.

The fuse holder had a poor connection, which caused both the burning and your charging problem.

Look at the wiring diagram.  Alternator output and battery are on the same side of the fuse.

I know. The black regulator terminal is the INPUT to the charging system, and if it is not supplied with sufficient voltage, the charging system will not perform to spec. Didn't you claim to be an EE??

[maxheadflow]

Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder.

The fuse holder had a poor connection, which caused both the burning and your charging problem.

Look at the wiring diagram.  Alternator output and battery are on the same side of the fuse.

I know. The black regulator terminal is the INPUT to the charging system, and if it is not supplied with sufficient voltage, the charging system will not perform to spec. Didn't you claim to be an EE??

If that were the case fuse would blow quickly.   If there were say a 1 volt drop at the fuse which is probably enough , bike uses say 7 amps while running. That 7 watts. The fuse would melt quickly and the bike would die. Obviously you are not a EE.

[Tracksnblades1]

Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder.

The fuse holder had a poor connection, which caused both the burning and your charging problem.

Look at the wiring diagram.  Alternator output and battery are on the same side of the fuse.

I know. The black regulator terminal is the INPUT to the charging system, and if it is not supplied with sufficient voltage, the charging system will not perform to spec. Didn't you claim to be an EE??

If that were the case fuse would blow quickly.   If there were say a 1 volt drop at the fuse which is probably enough , bike uses say 7 amps while running. That 7 watts. The fuse would melt quickly and the bike would die. Obviously you are not a EE.

Why would there be a 1 vdc drop across the actual 15 amp mini fuse. With a resistance values of 4.93-5.08 m-ohms, would the Voltage drop ever reach .1 vdc...?

[maxheadflow]

Fuse blew (15 amp) and burned pretty bad on one leg. Fuse is loose in the mini fuse holder.

The fuse holder had a poor connection, which caused both the burning and your charging problem.

Look at the wiring diagram.  Alternator output and battery are on the same side of the fuse.

I know. The black regulator terminal is the INPUT to the charging system, and if it is not supplied with sufficient voltage, the charging system will not perform to spec. Didn't you claim to be an EE??

If that were the case fuse would blow quickly.   If there were say a 1 volt drop at the fuse which is probably enough , bike uses say 7 amps while running. That 7 watts. The fuse would melt quickly and the bike would die. Obviously you are not a EE.

Why would there be a 1 vdc drop across the actual 15 amp mini fuse. With a resistance values of 4.93-5.08 m-ohms, would the Voltage drop ever reach .1 vdc...?

Because the clips that hold the fuse have become Ohmic. The heat from the poor contacts dumps directly into the fuse. It's the additional contact resistance that causes the voltage drop and heating.

[Dunk]

I have verified the output from the rectifier goes into the main harness and through a bullet connector plugs into the large battery cable from battery to starter solenoid. It is indeed a separate wire not going through the fuse, from the factory. This bullet connector was tight and clean.

I checked the battery age, January of 2013... Original from the winter I restored the bike. I got a new AGM battery, sadly dated about a year ago, 7/2018 if I recall correctly. They claim it's ready to go out of the box but voltage measured quite low, 12.3x I believe. I installed it and put it on the trickle charger.

I went over all electric connections again, cleaning and tightening connectors as I went. There were a few loose. I'll check them after a few rides and replace any that have loosened up again.

The battery was mostly charged by then so I started the bike and measured voltage as well as amps through the charge wire. Ballparking here as I don't have numbers in front of me, but voltage was over 12.6 at 1500 RPM with about 6-7 amps through the charge wire. With headlight on high beam voltage was 13.8 by 3000 RPM. Max amps I saw through the charge wire was 16 at about 5000 RPM with high beam on. That's with an inductive ammeter, so maybe not precise but should be in the ballpark.

I rode to work yesterday, headlight on the entire time about 17 miles each way. I did not notice gauge lights or neutral light dimming at any point. After getting home battery measured 12.624v. I'll check it again before my next ride and after riding but I think my problem is fixed. I'd say it amounted to an old battery that couldn't hold much charge and some loose connections causing voltage drop to the field coil and abnormally high amps pulled through the fuse.

[maxheadflow]

When you say 16 amps trough the charge wire, I assume this was the wire from the rectifier.

Sounds like you got it fixed. Good.

[calj737]

When you say 16 amps trough the charge wire, I assume this was the wire from the rectifier.

Correct me if I’m wrong, but letting 16v at an AGM battery is NOT good. It is a pretty clear indication of a reference voltage to the Regulator that is producing greater than 1.5v loss. 16v will cook a battery pretty quickly.

It sounds like Scottly’s premise of a fault on the Black wire to the Regulator still persists.

[bryanj]

Cal he said 16amps from generator not 16volt and that is actual more than the alternator is rated at

[calj737]

Cal he said 16amps from generator not 16volt and that is actual more than the alternator is rated at

Thanks for pointing that out. Please ignore my prior post.

[maxheadflow]

I am assuming that the measurement was at the charge wire.  With motor say at 5000 RPM,  and let's say the voltage at the battery is 13V, the alternator is putting out 208 watts.  Spec appears to be 210 watts at 5K.

[Bodi]

I don't believe the 16A (208W at 13VDC) into the battery.
With 210W total alternator output available (if everything is perfect in the wiring, and at 5000 RPM) that leaves 2W to run the ignition and lighting... not possible.
And 16A is too much charge current for a wet cell, probably for a AGM type as well. Usually charge current is rated at "10 hour rate", 1/10 the battery AH rating for wet cell batteries - a 16AH battery's charge current should be 1.6A. OK to go high for a short time, but things in the battery will be damaged if it's for very long.

[maxheadflow]

I don't believe the 16A (208W at 13VDC) into the battery.
With 210W total alternator output available (if everything is perfect in the wiring, and at 5000 RPM) that leaves 2W to run the ignition and lighting... not possible.
And 16A is too much charge current for a wet cell, probably for a AGM type as well. Usually charge current is rated at "10 hour rate", 1/10 the battery AH rating for wet cell batteries - a 16AH battery's charge current should be 1.6A. OK to go high for a short time, but things in the battery will be damaged if it's for very long.

That's why I said "at the charge wire". It would be total output of the charging system.  I agree. If it was at the battery, the current probe is miscalibrated (not zeroed?).

[Dunk]

Indeed 16 amps was at the charge wire off the rectifier, so most of that would be going to running the ignition and lights and a small amount to bring battery voltage up to 13.x. That's with a clamp on ammeter, Craftsman branded, so not the most precise instrument but should be in the ballpark.

 I've put a couple hundred miles on the bike, much of it commuting with some amount of sitting in traffic and always running the headlight on. about 3 hours after getting home today the battery measured 12.645v. I'll call my charging problem solved. It was a combination on a bad 6.5 year old battery and some loose bullet connectors. Sometimes it's the simple things.

Aside from that the ignition switch is a bit wonky lately. Sometimes I have to jiggle it a bit to get it to stay in the on position. It's an aftermarket, unknown brand as I don't feel like looking through receipts now. I think I was run with full load through it for a while, then eventually rewired headlight through relays. Also the tumbler is getting stiff, which could probably be resolved with some graphite lube. I'm a bit disappointed it's acting up after only 6.5 years and 6200 miles, but I may replace that proactively before spring. Is there an ignition switch generally regarded as good quality? Would it be worth putting the ignition on a relay to reduce current through the switch? I recall reading something from Hondaman about that.

[bryanj]

The relay in ignition is more to get full volts at coils so better spark but it would drop switch current which is not a bad idea, in fact use a relay to switch all the red to black current then only the relay coil current will go through the ignition switch and if you "hide" another switch in th line its an anti theft device OR something to forget and wonder why yhe damn thing wont go!

[RAFster122s]

EMGO switches can be dodgy and short lived, better to pony up for a real Honda switch or ignition switch, steering lock and helmet lock set (~$100-110)

[Dunk]

I did not realize Honda still made ignition switches. Looking up the part I see it is not a correct original style key and lock tumbler, and not matched to the steering lock that comes with it.
https://www.partzilla.com/product/honda/35010-315-017

I did find a matched original style set here (https://z1parts.net/ignition-switch-and-lock-set-cb-cl-sl-sandcast), though they don't say who makes it and while the keys are original style they do not have HONDA on them as originals do. Disappointing, but preferable to a new style key if the switch is good quality. Anyone use one?

Any other options? I suppose it'll be interesting getting the fork lock cylinder out without a key for it.