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View Full Version : Volts drop as RPM increases.....


mobilecascade
08-28-2013, 02:38 PM
Been searching threads.....

Been trying to figure out why at idle our volt / charging is great at 13-14volts, but when we get to skiing or boarding speed, our voltage drops to 10-11.... After a few minutes the low volt alarm comes on. It seems to do this over 2000 rpm. Obviously worse when the stereo (stock) is above 25% volume.

When parked (idle) we can run the stereo (up to kids 'full' volume) & no notable difference on the volt gauge. No alarm... For hours even...

Both batteries are fresh and 'full'. Leads/connections clean and 'lubed'... Good contact...

When pulling a skier and the alarm goes off, we just continue to give them a good run and do a quick shut off/back on during the fall/pickup to reset the alarm....

Have run the trickle charger on it overnight to see if maybe the batteries were on the edge.... Next day, same song....

Stock 02 XStar with LTR motor.... No crazy system. Stock clarion amps. No added bling lights...

Should i just replace the alternator. If so, is there a 'stock' bolt on and play to up the amperage. Ideas?

Being a past ford guy, I am assuming that the GM motors don't have the external voltage regulator like our old PS190....

ricford
08-28-2013, 05:02 PM
Sounds strange. How old is the battery? I would get it load tested first, before I spent the money on an alternator. You can also take the alternator to a motor rewinding shop to get tested too, before you spend money on something you may not need.
That being said, if you are sure all your connections are clean it's probably alternator, but I've never heard of your exact problem before.
You could also check with a voltmeter across the battery to be sure that your gauge is giving the correct reading.

chriscraftmatt1976
08-28-2013, 05:31 PM
Man, that's a weird one. It's battery or alternator, start cheapest first. Your belt good n tite?

petermegan
08-28-2013, 05:59 PM
Just a thought but check your wires on the back of your alternator. Pull them all off and check the wires aren't cracked. My alternator Earth just fell off in my hand the other day and if yours is hanging on by a couple of strands. Have Fun....

mikeg205
08-28-2013, 06:01 PM
check all the grounds and make sure there is no corrosion on the connections.

JimN
08-28-2013, 06:15 PM
Been searching threads.....

Been trying to figure out why at idle our volt / charging is great at 13-14volts, but when we get to skiing or boarding speed, our voltage drops to 10-11.... After a few minutes the low volt alarm comes on. It seems to do this over 2000 rpm. Obviously worse when the stereo (stock) is above 25% volume.

When parked (idle) we can run the stereo (up to kids 'full' volume) & no notable difference on the volt gauge. No alarm... For hours even...

Both batteries are fresh and 'full'. Leads/connections clean and 'lubed'... Good contact...

When pulling a skier and the alarm goes off, we just continue to give them a good run and do a quick shut off/back on during the fall/pickup to reset the alarm....

Have run the trickle charger on it overnight to see if maybe the batteries were on the edge.... Next day, same song....

Stock 02 XStar with LTR motor.... No crazy system. Stock clarion amps. No added bling lights...

Should i just replace the alternator. If so, is there a 'stock' bolt on and play to up the amperage. Ideas?

Being a past ford guy, I am assuming that the GM motors don't have the external voltage regulator like our old PS190....

A loose/worn belt would cause this. Load on the alternator causes resistance to rotation of the armature, so the alternator will resist turning when the crank pulley drives the belt(s). If it's the OEM alternator and you're trying to supply current to a lot more than it was designed for, you're not going to get the performance you want.

If it's an upgraded alternator, you can put a smaller pulley on it to make turning it easier. You'll need to replace the belt if there's not enough adjustment, though.

bstewart0529
08-29-2013, 09:22 AM
I have a 91 prostar and just replaced the alternator. I had the same issue with mine but i don't have an alarm that sounds. As I would throttle up to speed the gauge would go down to around 10 volts if not lower. I replaced the alternator and the main kill switch just two weeks ago. I haven't had any issues with the battery since then, however the volt gauge is now showing 14 at idle and then goes to around 12 when pulling. I too have gone through mine with a fine tooth comb and found nothing wrong with either the wiring or cables. I have replaced everything except the gauge it self. Since the alternator change I have not had one issue other than the gauge moving down when pulling someone. Strange is all i could say. I have worked on cars and boats my entire life and this one is just one I don't have an answer for yet.

JimN
08-29-2013, 09:29 AM
I have a 91 prostar and just replaced the alternator. I had the same issue with mine but i don't have an alarm that sounds. As I would throttle up to speed the gauge would go down to around 10 volts if not lower. I replaced the alternator and the main kill switch just two weeks ago. I haven't had any issues with the battery since then, however the volt gauge is now showing 14 at idle and then goes to around 12 when pulling. I too have gone through mine with a fine tooth comb and found nothing wrong with either the wiring or cables. I have replaced everything except the gauge it self. Since the alternator change I have not had one issue other than the gauge moving down when pulling someone. Strange is all i could say. I have worked on cars and boats my entire life and this one is just one I don't have an answer for yet.

Painted pulleys, or chrome plated? Either can allow the belt(s) to slip- how much play when they're tightened?

pkskier
08-29-2013, 10:11 AM
My gauge does the same thing, at idle 14 volts, rev the engine it drops down but never below 12 volts. With a meter I test the voltage at the battery and it never dropped, based on this I determine that the alternator is working fine. I also have never had a problem with the battery not being properly charged.

bstewart0529
08-29-2013, 10:24 AM
Mine are chrome. I will double check mine again before we head out this weekend and see if it makes a difference. good question though.

mobilecascade
08-29-2013, 12:25 PM
Ricford.... Batt's are only 2 years old. They are the regular "wet" style though...not the gel optimas or anything special. I'll check the voltage across the terminals to verify though. Thanks

Chriscraft... From what I can tell the belt is good with minimal slack.

Petermegan... Good thought on the alternator connection plug. I'll check that one..

Mikeg205.. All the connections that I have looked I've pulled, cleaned and put a dab of dielectric grease on... Other than the grounds at the batt switch, is there another spot you are aware of?

JimN... Yep, it's a stock alternator that came on the LTR.... I'll double check the belt as others have mentioned... Stock stereo FWIW

Bstewart0529 & PKskier.. So your leaning towards an alternator swap?


I feel the same.... If throttling up my assumption is that we're spinning the armature to give us a solid 14 volt +/- to keep the system charging... In the old days I would've swapped out a voltage regulator when I worked on our Jeep CJ or old pickup... That's been by the wayside over time with new rigs in the family... I'm assuming that there 'has' to be one internally on these alternators? Just stabbing at this one...

I'll hit up all the connections again and check that belt and verify the battery voltage.... Run it down the street and drop it in for a quick lap around the lake... Anyone need a quick pull? :).

Thanks everyone for all the ideas!! Much appreciated!

If we do go the R & R the alternator route, is there a higher output one that is a direct bolt in? And what are we talkin $$?

Table Rocker
08-29-2013, 12:42 PM
I would guess you have some resistance in your wiring somewhere. As the current flow goes up with higher RPMs, the resistance causes a greater voltage drop - Ohm's Law. Take your multimeter and measure voltage at various places along the path starting at the alternator. I had a voltage drop on the orange wire that runs from my alternator to the main fuse on the back of the engine. I replaced that wire and I also cleaned up where the alternator contacts the mount and the mount contacts the block to improve grounding.

Dielectric grease does not conduct electricity and should not be used on contacts themselves. It is used on things like spark plug boots to aid insulation and lubricate them for easy removal.

JimN
08-29-2013, 12:54 PM
Ricford.... Batt's are only 2 years old. They are the regular "wet" style though...not the gel optimas or anything special. I'll check the voltage across the terminals to verify though. Thanks

Chriscraft... From what I can tell the belt is good with minimal slack.

Petermegan... Good thought on the alternator connection plug. I'll check that one..

Mikeg205.. All the connections that I have looked I've pulled, cleaned and put a dab of dielectric grease on... Other than the grounds at the batt switch, is there another spot you are aware of?

JimN... Yep, it's a stock alternator that came on the LTR.... I'll double check the belt as others have mentioned... Stock stereo FWIW

Bstewart0529 & PKskier.. So your leaning towards an alternator swap?


I feel the same.... If throttling up my assumption is that we're spinning the armature to give us a solid 14 volt +/- to keep the system charging... In the old days I would've swapped out a voltage regulator when I worked on our Jeep CJ or old pickup... That's been by the wayside over time with new rigs in the family... I'm assuming that there 'has' to be one internally on these alternators? Just stabbing at this one...

I'll hit up all the connections again and check that belt and verify the battery voltage.... Run it down the street and drop it in for a quick lap around the lake... Anyone need a quick pull? :).

Thanks everyone for all the ideas!! Much appreciated!

If we do go the R & R the alternator route, is there a higher output one that is a direct bolt in? And what are we talkin $$?

The OEM case can be upgraded to about 105A.

mobilecascade
08-29-2013, 12:54 PM
So pull the alternator and clean the mounting points? Will try... Thanks!

Story for the grease term... I used the same grease that we used for our electrical panel swap at the house and for misc car stuff... Something the old man brought over when he did our splices and related thats been in the garage...

mobilecascade
08-29-2013, 12:56 PM
Jim... Is that something a Alternator Shop will do? Or is it something that needs to be sent off as a core to some part of the country? Sorry with the questions...

bstewart0529
08-29-2013, 01:37 PM
If you are looking for an up grade in amps?, then i got a 105 amp from DB Electric for $65. I was a bit skeptical at first but once i got it and installed it, i was quite impressed. The part number was ADR0334. I would make sure that you use a meter to measure at the battery, what the voltage is before you change it out. For me it was 12.5 at the battery, so i knew it was the alternator. Once the new one was installed i got 14.5 at the battery. I also made sure that once we increased the RPMs the 14.5 were still registering and they did. So i stopped caring so much as to what the gauge said.

JimN
08-29-2013, 07:20 PM
Jim... Is that something a Alternator Shop will do? Or is it something that needs to be sent off as a core to some part of the country? Sorry with the questions...

Yes. I use a shop on the West side of Milwaukee, but most cities have one, listed under Automotive Electric repair/rebuilding.

Shipping isn't cheap, but if you have a speed shop near you, ask who they use.