Engine Bay Blower voltage cycling between 14V and 10V - voltage regulator issue ?

[diversp]

Hi, appreciate any guidance given.

2017 Bavaria 34. In line blower from engine bay is vented via hose to cockpit near helm. I noticed that the noise from the vent goes up and down, corresponding to the fan speeding up and slowing down- which is noticeable. I changed the fan - same issue. I then checked the voltage across the fan and noticed every few seconds cycles between 14V and 10V. This is the causing the fan to speed up / slow down. The fan only comes on when the engine has started. Is this normal ?

My initial thoughts are faulty voltage regulator within the alternator. But in that sentence I have exhausted my knowledge. Thoughts

 

[PaulRainbow]

Hi, appreciate any guidance given.

2017 Bavaria 34. In line blower from engine bay is vented via hose to cockpit near helm. I noticed that the noise from the vent goes up and down, corresponding to the fan speeding up and slowing down- which is noticeable. I changed the fan - same issue. I then checked the voltage across the fan and noticed every few seconds cycles between 14V and 10V. This is the causing the fan to speed up / slow down. The fan only comes on when the engine has started. Is this normal ?

My initial thoughts are faulty voltage regulator within the alternator. But in that sentence I have exhausted my knowledge. Thoughts

If there are no other charging sources (solar, wind, etc) then it's possibly the alternator. Check the voltage at the batteries with the engine off, start the engine and check again. If it's normal with the engine off and fluctuates between 14v and 10v when it's running, take it to an auto electrician the repairs alternators.

 

[david_bagshaw]

Sounds more like a poor connection some where to me.

try a temp direct wiring to the fan from the battery, what happens then?

 

[VicS]

Hi, appreciate any guidance given.

2017 Bavaria 34. In line blower from engine bay is vented via hose to cockpit near helm. I noticed that the noise from the vent goes up and down, corresponding to the fan speeding up and slowing down- which is noticeable. I changed the fan - same issue. I then checked the voltage across the fan and noticed every few seconds cycles between 14V and 10V. This is the causing the fan to speed up / slow down. The fan only comes on when the engine has started. Is this normal ?

My initial thoughts are faulty voltage regulator within the alternator. But in that sentence I have exhausted my knowledge. Thoughts

Would not expect the volts reading to fall below the battery volts.

Why not monitor the volts at the battery or directly at the alternator output to be sure there's no problem with it

 

[pvb]

I have a 2014 Bavaria 37. The engine compartment fan is actually a 24v version (on a 12v boat) which I assumed was intended to reduce noise. The fan works, but it isn't in any way noisy. I can't see how the voltage reaching the fan can easily drop below the normal battery voltage.

 

[jiris]

To get to the bottom of it, you need more information. The first thing to do is check the voltage directly on the battery. If steady, you have a wiring problem at the lead to the blower. As the voltage at the blower is getting well below the value I would expect from a healthy battery (You don't have problem starting the engine, do you?), it is most likely this case. If you find similar fluctuation on the battery terminals, the battery would be the most likely suspect. Another possibility would be another high power appliance (engine glowplugs?) cutting in. The alternator would be the suspect - it wouldn't cause the voltage dropping below the normal battery voltage.

 

[pvb]

The alternator would be the suspect - it wouldn't cause the voltage dropping below the normal battery voltage.

Is that what you meant to post?

 

[jiris]

Is that what you meant to post?

Ops, thanks .
The intended response: "The alternator would be the LAST suspect - it wouldn't cause the voltage dropping below the normal battery voltage.

 

[PaulRainbow]

Would not expect the volts reading to fall below the battery volts.

Why not monitor the volts at the battery or directly at the alternator output to be sure there's no problem with it

Great idea, wish i had thought of that.

 

[PaulRainbow]

Ops, thanks .
The intended response: "The alternator would be the LAST suspect - it wouldn't cause the voltage dropping below the normal battery voltage.

You wouldn't think so, but what else do you suppose can raise the voltage beyond that of the batteries ?

 

[jiris]

You wouldn't think so, but what else do you suppose can raise the voltage beyond that of the batteries ?

Wouldn't be it a normal function of the alternator? Up to 14.8V it certainly would. If it stops charging, the voltage of an unloaded battery would drop to the level corresponding to its minute state. If load applied, obviously below that. But 10V indicates an extreme load, not likely consistent with the fan (100W?). Most protected appliances (inverters, heaters etc) would be cutting off well before this level.

 

[PaulRainbow]

Wouldn't be it a normal function of the alternator? Up to 14.8V it certainly would. If it stops charging, the voltage of an unloaded battery would drop to the level corresponding to its minute state. If load applied, obviously below that. But 10V indicates an extreme load, not likely consistent with the fan (100W?). Most protected appliances (inverters, heaters etc) would be cutting off well before this level.

But the "fact" that the voltage is fluctuating every few seconds doesn't follow the logic that the alternator cutting in/out would increase to 14v and then drop to the battery voltage, or less.

Additional checks, starting at the batteries are the way forward.

 

[jiris]

But the "fact" that the voltage is fluctuating every few seconds doesn't follow the logic that the alternator cutting in/out would increase to 14v and then drop to the battery voltage, or less.

Additional checks, starting at the batteries are the way forward.

Having some difficulties to identify the "logic" you are talking about or where there is any problem with my logic. But - whatever .

 

[RichardS]

Having some difficulties to identify the "logic" you are talking about or where there is any problem with my logic. But - whatever .

I believe that it's the voltage dropping down to 10V which is, presumably, below the normal standing battery voltage which seems to be the real issue. The normal thing which could drop the battery voltage from say, 12.5V down to 10V would be an intermittent large current drain, such as operating the starter motor or windlass but that clearly is not happening here.

It could be the alternator which is intermittently putting a massive current drain on the battery but I've never heard of an alternator failing like that and, if it could do that, I would have expected it to get very hot very quickly and then stop working altogether as the regulator burned out.

An intermittent short or problem connection might be a possibility but, as said by several above, one needs to start at the battery rather than the fan.

Richard

 

[jiris]

I believe that it's the voltage dropping down to 10V which is, presumably, below the normal standing battery voltage which seems to be the real issue. The normal thing which could drop the battery voltage from say, 12.5V down to 10V would be an intermittent large current drain, such as operating the starter motor or windlass but that clearly is not happening here.

It could be the alternator which is intermittently putting a massive current drain on the battery but I've never heard of an alternator failing like that and, if it could do that, I would have expected it to get very hot very quickly and then stop working altogether as the regulator burned out.

An intermittent short or problem connection might be a possibility but, as said by several above, one needs to start at the battery rather than the fan.

Richard

Well... Is it in any way anything else than what I was saying? Just asking .

 

[RichardS]

Well... Is it in any way anything else than what I was saying? Just asking .

I don't know. Paul would have to answer that.

Richard

 

[PaulRainbow]

I believe that it's the voltage dropping down to 10V which is, presumably, below the normal standing battery voltage which seems to be the real issue. The normal thing which could drop the battery voltage from say, 12.5V down to 10V would be an intermittent large current drain, such as operating the starter motor or windlass but that clearly is not happening here.

It could be the alternator which is intermittently putting a massive current drain on the battery but I've never heard of an alternator failing like that and, if it could do that, I would have expected it to get very hot very quickly and then stop working altogether as the regulator burned out.

An intermittent short or problem connection might be a possibility but, as said by several above, one needs to start at the battery rather than the fan.

Richard

Your first paragraph above is correct, although we can't be 100% certain something isn't being intermittently powered up and the OP hasn't noticed.

I have seen a few alternators fail in this way. They usually just fail completely, if they start off intermittently they don't usually last long. They do, as you correctly say, get very hot. I've seen them fail on cars catastrophically, with total loss of all electrical systems, in those cases the alternator was hotter than you'd be able to touch.

 

[PaulRainbow]

Well... Is it in any way anything else than what I was saying? Just asking .

In post #2 i have suggested taking voltage measurements at the batteries, to start with. That's the only correct answer in this case. It's pointless making wild guesses or dismissing anything, at this stage, with such little information.

Claims that the alternator "wouldn't cause the voltage dropping below the normal battery voltage" are incorrect, i've seen it happen.

Glow plugs on the OPs engine should not pull the batteries down to 10v.

"If you find similar fluctuation on the battery terminals, the battery would be the most likely suspect. " I have never seen a battery whose voltage has fluctuated between 10v and 14v.

That said, almost anything is possible, but until the OP takes some more voltage measurements and posts back, speculation and arguments are pointless and only serve to cause confusion.

 

[jiris]

In post #2 i have suggested taking voltage measurements at the batteries, to start with. That's the only correct answer in this case. It's pointless making wild guesses or dismissing anything, at this stage, with such little information.

Claims that the alternator "wouldn't cause the voltage dropping below the normal battery voltage" are incorrect, i've seen it happen.

Glow plugs on the OPs engine should not pull the batteries down to 10v.

"If you find similar fluctuation on the battery terminals, the battery would be the most likely suspect. " I have never seen a battery whose voltage has fluctuated between 10v and 14v.

That said, almost anything is possible, but until the OP takes some more voltage measurements and posts back, speculation and arguments are pointless and only serve to cause confusion.

Copied and pasted from my post No 6:

"To get to the bottom of it, you need more information. The first thing to do is check the voltage directly on the battery."

Each other point of your post can be discussed indefinitely, if the the objective is to prove how smart either of us is.
As my objective is more to help the OP to solve the problem, I am resting my case .

 

[diversp]

Thank you for guidance. I will now do voltage measurements at the both engine + service batteries while engine is running. Not too sure about the safety of measuring voltage across alternator while engine is running as sounds dangerous ?