Voltage gage spikes

ttmott said:
How does a single wire alternator know what the bat voltage is in this configuration?
Click to expand...

Alternator shouldn’t need to know as it produces a fixed voltage. The Diodes just keep the alternators from sending flow to opposite alternator or the batteries from feeding each other.
 
ttmott said:
There is also the chance one of the batteries resistance is dropping (shorting internally) and via the isolator causing the alternators to both go high in voltage and bringing the engire electrical system up in voltage.
Click to expand...

Thinking of starting with the batteries as I kind of don't like them and am looking for an "excuse" to replace. Is this something they can find during a load test?
 
ttmott said:
How does a single wire alternator know what the bat voltage is in this configuration?
Click to expand...

Tom, it is as @unsalted mentioned.

That diode pic is only a representation of how the old Guest isolators work. They were not very safe and screwed up a lot. The newer ACR's (Automatic Charging Replay) work incredibly well and what should be used in place of the old Guest when it dies.
 
Golfman25 said:
Thinking of starting with the batteries as I kind of don't like them and am looking for an "excuse" to replace. Is this something they can find during a load test?
Click to expand...

If there are cell(s) that are shorted or just dead, it will show up in the load test. But there isn't any test that will tell you which one it is. The load test will just fail or show very little amperage available.

I doubt what you are seeing is a shorted cell. It is most likely a bad alternator and/or a bad isolator as mentioned.
 
SKybolt said:
If there are cell(s) that are shorted or just dead, it will show up in the load test. But there isn't any test that will tell you which one it is. The load test will just fail or show very little amperage available.

I doubt what you are seeing is a shorted cell. It is most likely a bad alternator and/or a bad isolator as mentioned.
Click to expand...
I would agree. Just starting with simple and cheap and moving toward complicated and expensive. :)

Going to have the stbd batteries load tested, just to see, as they are a few years old and I don't know their history. Then I'll dig into the isolator possibility. And last but not least, alternators. That, plus some praying may get me there.
 
Golfman25 said:
I would agree. Just starting with simple and cheap and moving toward complicated and expensive. :)

Going to have the stbd batteries load tested, just to see, as they are a few years old and I don't know their history. Then I'll dig into the isolator possibility. And last but not least, alternators. That, plus some praying may get me there.
Click to expand...

Going back to your original statement of the Fox gateway(s) register the voltage spike. Do
have two Fox gateways? Or is there only one? If two then do both register the spike?

Because if only one does then you have your culprit, that engines alternator.
 
SKybolt said:
Going back to your original statement of the Fox gateway(s) register the voltage spike. Do
have two Fox gateways? Or is there only one? If two then do both register the spike?

Because if only one does then you have your culprit, that engines alternator.
Click to expand...
Two, one for each engine. Each one measures the spike at the same time and mirrors the gages. Each side has a slightly different reading -- between .1 and say .3 volts different.
 
Golfman25 said:
Two, one for each engine. Each one measures the spike at the same time and mirrors the gages. Each side has a slightly different reading -- between .1 and say .3 volts different.
Click to expand...

So that is the part that has me a bit baffled. How do both ECM's see the same spike from a bad battery. I get if the isolator or Alternator goes bad then that could happen. But not from a bad battery.
 
SKybolt said:
So that is the part that has me a bit baffled. How do both ECM's see the same spike from a bad battery. I get if the isolator or Alternator goes bad then that could happen. But not from a bad battery.
Click to expand...
I don't really know. But have to start somewhere. Wiring, batteries and isolator seem like the places to start.

I am highly suspect that both alternators are going bad at the same time, let alone that they would spool up extra voltage at the same time.
 
Golfman25 said:
... I am highly suspect that both alternators are going bad at the same time, let alone that they would spool up extra voltage at the same time.
Click to expand...

Same here and why I brought up the isolator.
 
unsalted said:
Alternator shouldn’t need to know as it produces a fixed voltage. The Diodes just keep the alternators from sending flow to opposite alternator or the batteries from feeding each other.
Click to expand...
The alternators have to sense a load (voltage) to turn on and set their field ground bias for a stable output. The battery voltage is the means to do that. The lower the battery voltage the higher the current; higher current coincides with a higher output voltage. With the diodes preventing any battery voltage at the alternator there is not a stable way to set the charge parameters. There are one wire alternators that use that main B+ to govern the field and there are 3 wire alternators that use a separate wire to control the field.
 
ttmott said:
The alternators have to sense a load (voltage) to turn on and set their field ground bias for a stable output. The battery voltage is the means to do that. The lower the battery voltage the higher the current; higher current coincides with a higher output voltage. With the diodes preventing any battery voltage at the alternator there is not a stable way to set the charge parameters. There are one wire alternators that use that main B+ to govern the field and there are 3 wire alternators that use a separate wire to control the field.
Click to expand...

Tom, Sea Ray used the Guest (or Pro-mariner) isolator for years as part of their standard build. Chevy used the 1 wire alternator for years as well. The diode pic I posted was a representation of how it works, their is other circuitry in the isolator so the field is energized and the dc exciter voltage is present. I am not sure when SR stopped using the Guest isolator and moved to the ACR but is was well into the 2000's before that happened.

As you can see in the other pic I marked up, the isolator is present and only one wire from the alternator to the isolator and batteries.
 
SKybolt said:
Tom, Sea Ray used the Guest (or Pro-mariner) isolator for years as part of their standard build. Chevy used the 1 wire alternator for years as well. The diode pic I posted was a representation of how it works, their is other circuitry in the isolator so the field is energized and the dc exciter voltage is present. I am not sure when SR stopped using the Guest isolator and moved to the ACR but is was well into the 2000's before that happened.

As you can see in the other pic I marked up, the isolator is present and only one wire from the alternator to the isolator and batteries.
Click to expand...
Ah, that makes sense - Thanks!
 
So took a run to the boat. Looking like it’s the isolator according to what is see via testing on you tube. With my meter. One side I get a good reading from alt (red) to battery (black) (like .4-.6). I also get a reading when reversed battery (red) to alt. (Black) (Like 1.2).

Other side checks fine with no reading from battery to alt.
 
Golfman25 said:
So took a run to the boat. Looking like it’s the isolator according to what is see via testing on you tube. With my meter. One side I get a good reading from alt (red) to battery (black) (like .4-.6). I also get a reading when reversed battery (red) to alt. (Black) (Like 1.2).

Other side checks fine with no reading from battery to alt.
Click to expand...

So it's probably what I was saying about the isolator breaking down. The reverse reading is fine as that is the circuit that allows the alt. to charge.

The .6 is the knee voltage of a the circuits diode equivalent. The .2 or so, is what feeds the field winding on the alternator. That open you are seeing can act like a cap charging and dis-charging and why you are seeing the voltage spike.

@Golfman25 feel lucky, it's a very rare occurrence that this happens. :eek:

Be careful when you replace the isolator, it is possible that the alternator took out the isolator. If you runt he engine now, before replacing anything, you should be able to monitor the alternators voltage at the isolators input. Make sure that the voltage there is ~ 14v when the idle is up over 1K RPM's.
 
Quick update. Replaced the batter isolator. At idle both gages reading 13.6 ish. We’ll need to see if it solves the problem long term.

one question though. Checked the port batteries when disconnected. They were showing 13.24 volts. Seems a bit high when disconnected. Starboard read good at 12 and change.
 
Golfman25 said:
Quick update. Replaced the batter isolator. At idle both gages reading 13.6 ish. We’ll need to see if it solves the problem long term.

one question though. Checked the port batteries when disconnected. They were showing 13.24 volts. Seems a bit high when disconnected. Starboard read good at 12 and change.
Click to expand...

When you disconnect the batteries from the charger it will take ~30 for them to settle. But good batteries fully charged should read ~12.7/8 volts. Lead acid that is.
 
SKybolt said:
When you disconnect the batteries from the charger it will take ~30 for them to settle. But good batteries fully charged should read ~12.7/8 volts. Lead acid that is.
Click to expand...
Ok thanks. Was probably only a few mins after I disconnected.
 
You must log in or register to reply here.

Forum statistics

Threads
113,219
Messages
1,428,826
Members
61,115
Latest member
Gardnersf
Back
Top