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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.

Capt. Jack
06-01-2014, 10:15 PM
I have a 2005 X-Star MCX engine, lat fall the alternator went out, I had it rebuilt at a local shop and this year on start up I noticed the volt gauge was below 13 volts, uses to run 14+ pre rebuild. Batteries are only a season old and have been charged up and I get a similar alarm as above. Idling around we are fine throttle up to pull a surfer and the voltage drops and the alarm sounds. I turned off all accessories, ballast pumps, radio ect. I need to go back to the marina and do some testing this week but I am suspecting a back connection or bad alternator again, strange for just being rebuilt.

JimN
06-01-2014, 10:46 PM
I have a 2005 X-Star MCX engine, lat fall the alternator went out, I had it rebuilt at a local shop and this year on start up I noticed the volt gauge was below 13 volts, uses to run 14+ pre rebuild. Batteries are only a season old and have been charged up and I get a similar alarm as above. Idling around we are fine throttle up to pull a surfer and the voltage drops and the alarm sounds. I turned off all accessories, ballast pumps, radio ect. I need to go back to the marina and do some testing this week but I am suspecting a back connection or bad alternator again, strange for just being rebuilt.

Same pulley? Call the shop and ask if they put the OEM pulley on, or did it come with a different one of larger diameter? You may want to use a smaller pulley- it will spin the armature faster AND put less load on the engine.

curver900
06-02-2014, 03:18 AM
I had this exact thing happen on a motorcycle, turned out it was a under performing regulator/rectifier.

Table Rocker
06-02-2014, 09:21 AM
If your alternator has been repainted, make sure and sand the paint off where it mounts. The alternator case and the mounts are your ground path.

Capt. Jack
06-02-2014, 11:22 PM
Here is an update, I took the meter down to the marina today and tested voltage drops, loose connections, the battery isolator and put a meter about every place I could think. I finally went to the alternator and clipped the leaders directly to alternator and again at the isolator and I measured 24.5 volts at an idle. I am taking the alternator back to the rebuild shop. I don't completely understand what all the components are or how they work with the MC dual battery system, it would be nice if MC would publish a wire diagram or any tech info. Anyway I will update in a day or so.

JimN
06-03-2014, 08:37 AM
Here is an update, I took the meter down to the marina today and tested voltage drops, loose connections, the battery isolator and put a meter about every place I could think. I finally went to the alternator and clipped the leaders directly to alternator and again at the isolator and I measured 24.5 volts at an idle. I am taking the alternator back to the rebuild shop. I don't completely understand what all the components are or how they work with the MC dual battery system, it would be nice if MC would publish a wire diagram or any tech info. Anyway I will update in a day or so.

If you read 24.5VDC with a good meter, it would seem that you may have connected the probes in a way that read the batteries in series, possibly on the isolator. What did you read at each battery?

You might want to take the boat to the rebuilder, so they can inspect the wiring and tell you if something is connected improperly.

Your isolator's manufacturer should have diagrams on their website- use that as a guide. Wiring the batteries in series an damage the boat's electronics.

Jeff d
06-03-2014, 09:13 AM
What did it read at the alternator with the engine not running? That would tell you pretty quickly if it's the alternator or your battery wiring.

Capt. Jack
06-04-2014, 12:01 AM
So I took the alternator back to the rebuild shop and it tested fine, 14.4 volts on the bench. The wiring in the boat last year was the same and worked fine. So tonite I tested the batteries 12 volts at each I also tested the isolator with the battery switch in all three positions and I read 12 volts, I even tested the sensing wire that tells the voltage regulator when to charge, and 12 volts. I hooked the alternator up and checked the terminals of the alternator 0 volts, I started the engine and immediately the leads on the alternator read 24.5 volts, tested the batteries and they still read 12 volts. The only thing I can figure at this point is that the original alternator did not have the purple and red wire connected to the same terminals. I am headed back to the alternator shop tomorrow and see what the P L I and S terminals should be connected to, not sure where to go after that other than perhaps the isolator?

Table Rocker
06-04-2014, 09:45 AM
I would simplify the system to make sure it worked and then add things back in slowly. I would test with one battery first.

It sure sounds like you have two batteries in series to get the 24.5 volts. I don't think there is any other way to get there.

Capt. Jack
06-04-2014, 09:53 AM
I would agree, but with or without the alternator running I can not measure more than 12 volts anywhere in the boat. It may also be the isolator?

Table Rocker
06-04-2014, 10:02 AM
I know nothing about isolators, but all the battery grounds should go to ground and the positives would go to the isolator. At least in my simple way of understanding. I would temporarily remove it while figuring out the problem.

Jeff d
06-04-2014, 10:25 AM
For the OE 51 amp Leece-Neville alternator on the LTR (Not the LT-1 but possibly similar) the three wires consist of: +12 ignition switched wire, a ground for the regulator, and a larger gauge charging wire.

I don't remember which wires were which colors but that may not be applicable to your boat anyway. It could be possible that if the wires are hoked up wrong you'd see the series voltage of your battery + the alternator's output.

It should be noted that the factory setup/leece neville alternator "3 wire" setup on my boat was NOT what the three wires of a typical "3 wire" alternator would have. A more typical "3 wire" alternator would not have a distinct ground wire but rather ground through its own mounting bolts. The three wires would consist of a constant +12 volt "input", a +12 volt "output" for charging, and an ignition switched +12 volt wire. I suppose another possibility would be that the rebuilder took things apart internally without noting this difference vs. the standard and proceeded to set it up in the more typical manner upon reassembly.

Jeff d
06-04-2014, 10:53 AM
Test this scenario (All assuming that your alternator wiring is the same as the LTR):
Hookup the ignition switched wire and the regulator ground wire to the alternator but leave the charging lead (the heaviest gauge of the 3, probably connected to a post on the body) disconnected. Start the engine and test voltage on the charging post. What do you get there? Test the voltage on the disconnected charging lead. What do you get there?

Potential Outcomes and Implications:
-If the alternator is still outputting 24 volts then you can be sure it's not battery or isolator related. Bring the alternator back and tell them it's not right.
-If the alternator charging post is only outputting the expected ~14 volts then you know your alternator is good.
-If the disconnected charging lead is only outputting 12 volts then you know the batteries/isolator is wired up right
-If the disconnected charging relay is ouptutting 24 volts then you know you have an isolator/battery configuration issue.
-If both tests show 12-14 volts (But it jumps back to 24 volts when you reconnect the charging lead) then you know it's an alternator wiring harness/connection issue that's effectively putting the battery voltage in series (It should be in parallel) with the alternator charging voltage.

Capt. Jack
06-04-2014, 12:30 PM
Test this scenario (All assuming that your alternator wiring is the same as the LTR):
Hookup the ignition switched wire and the regulator ground wire to the alternator but leave the charging lead (the heaviest gauge of the 3, probably connected to a post on the body) disconnected. Start the engine and test voltage on the charging post. What do you get there? Test the voltage on the disconnected charging lead. What do you get there?

Potential Outcomes and Implications:
-If the alternator is still outputting 24 volts then you can be sure it's not battery or isolator related. Bring the alternator back and tell them it's not right.
-If the alternator charging post is only outputting the expected ~14 volts then you know your alternator is good.
-If the disconnected charging lead is only outputting 12 volts then you know the batteries/isolator is wired up right
-If the disconnected charging relay is ouptutting 24 volts then you know you have an isolator/battery configuration issue.
-If both tests show 12-14 volts (But it jumps back to 24 volts when you reconnect the charging lead) then you know it's an alternator wiring harness/connection issue that's effectively putting the battery voltage in series (It should be in parallel) with the alternator charging voltage.

Thanks for all the great info, I have the MCX engine and the AC Delco 11SI alternator, the engine harness is a two wire hook up. I will test the scenarios tonite and hopefully report back.