Can you Harley or Electrical boffs answer this one?

Question

Ok battery went dead. New battery fitted not long ago. New rectifier also. Checked the output from the alternator and seems fine with 13.5 - 14.5 volts AC.(Before the connector block,so getting feed from the Alternator) When I connect the connector block from the alternator to the rectifier back up it only reads around 4.5 AC. Is this normal? Had this problem a few months ago and it was a lose connection at the connector block. Ive checked them and they seem fine as when I check output voltage at the block(disconnected) the voltage is as above.Its only when I connect it al back up that I get this reading.
Anybody?????????

Answer 1

Alternator should put out more than 13~14 volts,,,way more.

It's Unregulated AC current.

If You're testing Directly from Alternator,,,and at whatever specified "max rpm" voltage should be Beyond 40VAC on each wire pair


Though Diodes in the Rectifier are intended to serve as mere "check valves" and cut-off Half the A/C wave resulting in DC Current,,,,
They DO also act as Resistors and will drop the voltage going thru them


So when you send your Alternator's Hi Voltage AC thru a rectifier,,,,
That's CUT IN HALF by the Diode's rectification action.
It's FURTHER Reduced by the Diode's Resistance properties.


Your Alt reads an avg 14VAC now,,,Cut that in Half and your already down to 7.
Subtract a Volt or 2 for Rectifier's RESISTANCE,,,and You're then down to 5~6V DC

A Reduced Alt Voltage Output also drops it's amperage capacity.
Lower Amperage output always results in a larger voltage drop under load.

"Load" is the Rectfier's resistance,,,and can even be the tiny resistance of the Meter itself.
All adds up.

W/ 13.5~14.5 VAC at the alternator output,,,,,no wonder it's down to 4's w/ Rectifier connected.

(The Rejected half of the AC's sine wave is shunted to ground,,thus doesnt contribute to total voltage when Rect is connected in circuit)
AC gets "rectified" either way.

Thats waht creates the distinct (-) which exists thru chassis.
On Negative ground systems ,of course.
Positive Earth sys's are opposite

.......................................
DOUBLE CHECK that Alternator Output.
Straight Outa the Alternator with Nothing Connected,,
Each Pair oughta gen enough AC Voltage to SCARE You.

40 to 60 VAC range.

Maybe somebody's got a Manual,,or you can find exact Voltage Specs.
I got neither time nor interest,,,lol

But regardless of whatever actual specs may be,,,
A nominal 12vdc system driven by a AC Alternator is BOUND to produce at least 25~30+ Volts AC BARE MINIMUM in order to have 12 Volts or More DC left available after rectification.

Rectifier Resistance Added in,.,,,raises that "Minimun AC" requirement BEYOND 30V raw ac output from Alternator

If Ya cant Find 30VAC at alternator,,MINIMUM at anything much above Idle,,,
then Alternator itself is Highly Suspect as having Low Output.

That may be a Bad Coil,or hi resistance in a winding(faint short),,,
or as simple as bad output wiring or corroded connectors,or bad crimp on a connector/corrosion at the crimp


it COULD be a Bad Rectifier,,,if it's sending one whole leg of AC to ground via a Diode shorted to ground.
That's Possible but very rare,almost unheard of.
They usually just Fail Open,,where nothing gets thru.

But on a Full Wave/3 phase sys,,,It CAN "backflow" a different phase back to ground.
Batt goes dead while sitting ,,due to the direct drain.
And Output is LOW


Remove Rectifier,,,and check it with an Ohmmeter.
You should get NO continuity to Ground on any of the output pins ,,,Until You REVERSE the meter's leads.
Not even on High resistance scale.
Rx10,,Rx100

Direct & Full Connection in One Direction,,,
ZERO connection in Opposite direction.
On Rect's output side.

If Rectfier checks OK to Ground,,,
And Alt output is within range---30VAC or better.....
Then I just dunno what.

Dont trust those crimp on connections or take them for granted as BEING OK cuz the LOOK ok.

They can have a LOT of resitance when corroded under the crimp where y cannot see it very well at a glance.

Double check your test procedures,,
and double check the component's output while each is isolated from rest of system.

I hope it's You getting goofy numbers,,,and Not the bike.
You & me Both do :)

Good Luck with it,,hope ya find it easily and it's nothing terrible.


* Put Battery on Slow Charge.
If by chance it's received AC via a bad rectifier that's murder on a Battery.
A slow Charge can sometime save a bat thats have limited exposure to ac,,,,or it can reduce damage somewhat and restore a little of the lost life expectancy for the batt.

Depending upon what exactly has failed,,,,it's a possibility Battery is actually "DEAD",,and not merely discharged.
Dont be surprised if a replacement Batt is needed Now or Soon as a result of AC Damage to Battery.

Just a heads-up on that POSSIBILTY.
Otherwise it may be a frustrating mystery a few days/weeks after ya get it all actually FIXED,,,to find you Battery Dead Again.

It Happens,,but Maybe Not,,,,tuff to predict.

Good Luck with it

Answer 2

First of all, stators don't wear out, they charge too little because the insulation covering the wires in the winding has broken down and shorts the wires out. With the bike running, first check the voltage at the battery terminals as the other fellow mentioned. At an idle, you may have slightly less than 12 volts DC, but that should get up to 14.5-14.7 DC volts when you speed the engine up. With all the lights on and running lights on, it may show voltage in the 13's, but that's still ok. If it sets at around 11.25 volts and never moves, it's likely the stator is shot. To check it, you'll have three wires coming directly from the alternator. With your multimeter, you should get the aforementioned 70 volts AC (give or take) when you check the wires in pairs with the engine running. You'll have three pairs, left & middle, middle & right and right & left. If the voltage is considerabaly less on any one of the pair, the stator is shot and it's time for a new one.

If the voltage at the battery is ok, then it's time to check the cable connections for corrosion. If the battery has removable caps, get a el-cheapo ball hydrometer and check each individual cell. The thing to look for is a difference between the cells. If all 6 cells are at say, 25% charge, then you know the battery isn't being charged and you need to look elsewhere. If 5 cells show 100% and one is 25%, then it's a bad battery. New mototcycle batteries are shipped dry and after adding the electrolyte, they need to set for a while to give the plates a chance to absorb the liquid. They should also be give a very slow charge before throwing them into use. If you failed to do this, it may be a battery problem. Put the battery on a low charge for a day and check the cells with the hydrometer. Check several days later and if you haven't used it, they should still be full charge or if you've cranked on it, they should be in an even state of discharge.

If the voltage at the battery shows low but output at the alternator is good, then it's somewhere inbetween. On my buddy's old Harley, there was a wire from near the battery that led to the regulator rectifier that became corroded from battery acid. I found and fixed that problem while nearly being run over by semi's along a busy interstate near Boston.

Does the battery go dead after setting overnight? Or after a lot of use? If the former, charge the battery up and disconnect a battery cable and see what happens. If it's still up, there's a drain somewhere. It may be something like the radio failing to shut off or a bad diode in the rectifier. My same buddy's new Harley will randomly drain the battery overnight. Not every night, but just every so often. On this years trip, I had to jump his bike 2 out of 10 mornings. I've never had a chance to throughly check it out, but so far I'm stumped. If your acts the same way, then I'm sure it's not any of the above problems. If anything, I'm suspecting it's somehow losing juice through the audio system, either the radio or the amplifier.

Answer 3

I'm not sure where you are taking your readings at.
Output from the alternator is AC and should be in excess of 100 Volts. This goes to the rectifier/regulator where it's transformed to DC and regulated down to approx 13 Volts.

I can't give you a good answer as I'm confused as to your test points and your measurements. Are you changing the scale on the meter?

Answer 4

Dude, it's A/C off the alternator, once it has gone through the rectifier/regulator it becomes D/C ( it's been rectified) .
It should read at least 11.5 volts D/C and up to 13 with the RPM up.

Answer 5

No, it is not, ck voltage at battery running, should be 13.5 to 14.5 if not, go back to rectifier, if 13.5 - 14.5 going in and 4.5 coming out, you have a cracked or blown rectifier.

Answer 6

if this problem has occured before , check for loose electrical wireing around the the connector blocks, good luck .ripnburned

Answer 7

Move to the OTHER side of the equation and check your grounding. Perhaps your ground cable is worn, frayed, or even missing a good connect in the back-loop?? That can be a real forhead-slapper,,, duuuuuuh.

Answer 8

You should be getting somewhere around 70v ac right off the alternator,

Answer 9

poor ground off battery

Answer 10

you need to let someone know what your talking about ? make / model/ etc / or buy a bicycle