Topic: Alternator charging higher with headlight on?

[Dunk]

Battery on my K5 was dead the other day after sitting off for a couple weeks. Not sure age of battery of if there's a drain. It has a Dyna S, 3 ohm coils, and I just installed a 60/65 H4 headlight after it was dead. My K1 has the same setup. I measured voltage to see if the charging system on the K5 was working, as it was weak previously. I cleaned connections and ncleaned/adjusted the voltage regulator some months ago. Wanted to see if it was too weak for the Dyna and headlight. What I found was strange. Freshly charged battery stabilized around 12.3x volts Slightly discharging at idle but charging by 1200-1500 or so.  The bizarre part is it increases by about a volt when turning on the headlight, voltage increases. Regulator and rectifier are old or original on the K5.

K5:
Battery (off): 12.3x
3k headlight off: 13.7x
3k headlight on: 14.7x

This had me intrigued, so I fired up my K1 and checked it. Rather attempted to fire it using the starter, which I never use, and it wouldn't barely crank. Checked battery and voltage was quite low. Kicked it over and checked voltage, which I found to be more what I expected and the slightly low voltage with the headlight off I attribute to the battery being quite drained. Rectified is about 2 years old and regulator is original and has not been cleaned or adjusted by me.

K1:
Battery (off): 11.3x
3k headlight off: 13.1x
3k headlight on: 12.3x

What's the deal with these, particularly the increasing voltage with higher load on the K5. With headlight off it's slightly less charge than I'd like, but with headlight on is boarderline overcharging. With a bit more RPM it goes to 14.8x then drops back down to 14.6-14.7 presumably from the Dyna pulling more amps at higher RPM.

What should I be checking? Will going to a new solid state regulator+rectifier help? Should I change to a lower wattage headlight? Maybe pull the trigger on Anders high amp alternator? Apparently my K1 has a charging problem that I've been unaware of since I always kick start it and usually ride in the day with light off if I'm in stop and go traffic.

[calj737]

To me, your K5 is doing what I would expect; producing more charge due to a higher drain. You K1 is irrelevant because the starting voltage was already low, and is definitely not producing surplus voltage by 3K RPMs. But you need a fully charged battery to start your tests so both bikes are on equal footing.

[scottly]

Since you have it handy, swap the K1 regulator into the K5 and run the same test with the headlight on and off. If the voltage still increases with the headlight on, suspect the wiring on the K5. If not, suspect the K5 regulator that you had previously adjusted.

[Dunk]

Got a OMP solid state regulator for each bike. Installed and checked voltage again with  batteries each starting at about 12.1x volts and kick starting so no high drain to recover from. The K1 now reads more as expected. Slightly discharging at idle but charging by 1500-200 RPM (with headlight on, barely), and about 14.6 volts at 3000-4000 depending on headlight off/on. So basically pushing the system with this load but if actually riding it should be alright. I may look into a headlight bulb with a 35 watt low beam, higher resistance coils, or the alternator upgrade.

The K5 still increases voltage with the headlight on. It reaches roughly 14.6 just over 3k RPM, but switch the headlight on at that RPM and voltage goes to about 15.5. Lower RPM and voltage seems to be limited to whatever the alternator can put out. Hmm... It just hit me maybe I have a short somewhere where the headlight switch is connected to the field wire, headlight on puts alternator full field and overcharges. I'll have to check for that.

In any event, I tested the rectifier on both bikes and there is continuity only one way, as described in the manual. Not sure what else could cause this other than a short as I mentioned. As for the new solid state regulators, I didn't record numbers but my observation was a slight improvement in charge voltage, mostly at lower RPM.

[Dunk]

Checked field wire voltage in harness with regulator disconnected.

K5:
Ignition on, headlight off: 0.00v
Ignition on, headlight on: 0.06v

K1:
Ignition on, headlight off: 0.00v
Ignition on, headlight on: 0.01v

Thoughts?

[CB750F2]

Dunk,the regulator uses the voltage at the black wire as the input to the regulator. There will be a voltage drop on the black wire which increases under-load and the regulator tries to correct this and so the output of the alternator increases and thus you see an increase in voltage across the battery when under load. The voltage at the black wire should be around the 1.0 to 1.25 volts less than battery voltage. If the drop is excessive your options are :- Clean all connections including switches or install a relay with the coil switched by the black wire and the relay contacts switching battery voltage to the the terminal on the regulator where the black wire would normally connect to. Pat

[calj737]

The voltage at the black wire should be around the 1.0 to 1.25 volts less than battery voltage.

Not to start a bickering match, but this is not accurate. The BLACK wire should be as close as possible to the battery to prevent over-charging. If you do find BLACK has greater than 0.05v less than the battery, you definitely need to maintenance your connections and harness and find the culprit of the added resistance. If you do not attend to this, you will burn up your battery.

Common culprits are the non-stock ignition switch, badly corroded connectors on the fuse panel and regulator blocks, as well as any/all ground locations. Madmtnmotors (Wilbur) has an excellent link in his signature for performing all the maintenance to restore your harness to 100%. Worth a good read and effort.

[Dunk]

Thanks, reference voltage to the regulator is the problem. I directly measured voltage drop between battery positive terminal and regulator black on both bikes, engine off and headlight off/on. The K1 is a couple year old restoration with all new wiring and igition switch. The K5 is more of a hodge-podge to make it a decent rider, details unknown as I got it like this though it appears to have a new harness.

K1:
Light off: .28v
Light on: .37v

K5:
Light off: .87v
Light on: 1.36v

I'll check the ignition switch first but also go over the rest of the wiring and connectors. Any common points to check?

[Dunk]

I cleaned several connections and while doing so found the main wire off the battery was pretty cooked inside the insulation. Replaced that with a piece of 12ga with a ring terminal at battery end and a bullet to connect to the harness. In hindsight I probably should have just put a ring on the harness and connected it straight to the solenoid. Maybe I'll do that at some point. In any event, big improvements in voltage drop between battery lug and the regulator sense terminal, but still high with the headlight on. Still some improvement to be made but I think I found the biggest part of it.

K5:
Light off: .25v
Light on: .91v

[Bodi]

I don't believe you'll get down to a 0.05V drop on any of our bikes with a stock harness between the battery + and the black wire to the regulator. There's just too much wire (plus the keyswitch) between those points. With just-cleaned connectors and switch I get around 0.5 volts. On bikes that haven't seen harness maintenance 1.0-1.5V is typical for the better ones. At some point the problem compounds and the drop is so great that the regulator is always on but the field coil gets the lower voltage as well... so the alternator can't make much power: the battery doesn't gas out from overcharging, it never fully charges with weak/no electric starting and the lights visibly dimmer at idle.

[Dunk]

.05v drop to the regulator isn't going to happen. I get .06v drop just through the ignition switch itself and it appears to be a new switch.

[calj737]

.05v drop to the regulator isn't going to happen. I get .06v drop just through the ignition switch itself and it appears to be a new switch.

Time to refurbish your harness. Follow Wilbur's thread in his signature (madmtnmotors) for details.

[Dunk]

For what it's worth the K5 is now charging more as expected. Max voltage starting at ~12v battery was 14.4x around 3000 RPM, 13.5x with headlight on at slightly more RPM. The K1 has relays on the headlight, the K5 does not. I'm thinking maybe it's too much current though an old headlight switch which may have dirty contacts that have never been cleaned. I'm making a relay harness for it now and will see how that affects things. Will also clean all connections in the bucket.

Calj, time to refurb the harness on both bikes? The K1 is a ~2 yr old restore with mostly new wiring, switches were disassembled and cleaned, replaced all connectors from the switches on the bars, etc. Only been in the rain twice. The K5 seems to have been slapped together quickly by PO, some new parts, some odds and ends repaired or replaced but general lack of attention to detail. It does have a new harness, key switch, regulator, and misc connections though.

[scottly]

Like Bodi said, .5V drop to the black reg terminal is as good as it's going to get.
Dunk, dirty contacts in the headlight switch wouldn't increase the current draw, it would reduce it. Go ahead and install the relay for the headlight, as it will take that much load off the key switch and main fuse, which can't hurt.

[Dunk]

K5 voltage drop to regulator black wire with headlight relays:
Light off: .31v
Light on: .52v

Almost cut the drop in half vs no relays.