Quiz Bottle of Wine for the winner

[IanR]

Ok chaps here is your quiz of the week

Scenario

Bilge blower intermittently stops blowing, works at low revs but frequently cuts out, can't hear at higher revs, bit think cuts out too. obviously stopped working later too as engine bay very hot. Engine BTW is Yanmar 3GM. I first assume that brushes on the blower are worn and decide to replace. (Duh moment 1)

Action 1 replace bilge blower with one bought from Chandler 25 squids down

Nothing worked, worked way through wiring to relay and cheched OK, relay links to blower via start motor. (Duh moment 2) Went to Halfords and various trying to buy a Hella relay but could only buy flasher units so went back and tried various plans including swapping out relay and direct connecting supply 12V to blower (No Go) Eventually disconnected all parts, checked all fuses (strategically hidden in depths of engine bay) and discovered replacement blower was short circuiting and cutting out after 2 secs by overheating, boat is 12v and DC motor must have been 6V. (Duh moment 3)

Went to chandlery and tested blower they suggest it was 6v motor and a fire risk (you don't say!), I swapped out for proper 12v model, installed ok , tested ok. (Oh really - then read on!)

Then put boat back together, tie wrap all wires neatly etc.. etc.. you know the routine, blower seems to work, smug grin of satisfaction despite troubleshooting having taken almost 12 hours for a simple DC motor!

Then find bilgeblower cuts out at high revs and only starts up again intermittently at low revs, wiring for bilgeblower is 12v from starter motor through to relay fed by 12v from starter moter (don't understand this duplex wiring). (Next Duh moment)

It seems like there is not enough voltage at low revs on starter, could this be because alternator is robbing voltage? Also I could put voltmeter on engine but have unnatural reluctance to get close to engine with fan belts spinning to get to test points strategically place in bowels of engine bay......

So how do I troubleshoot this beast?

Please bear in mind that engine room , fuses and connections are tucked in back of small cupboard where only double jointed pixies need apply! Can anyone help me understand for instance, why is there a relay and why not wired direct to ignition key and why I should not wire up to a relay placed behind ignition key.?

I will be honest I am not really an electrician, so I am not sure if I have understood this, my arms are ripped to shreds having been doing gynaecology through the keyhole for hours on end. No laparascope and therefore still not fixed it yet if anyone can help me understand and repair this pain in the RCE I will post you a decent bottle of vin rouge

anticipating in optimism
Answers on a post card please

 

[supermalc]

I too am not an electrician, and usually miss the obvious, so you have my sympathy.

However, my first thought is if there is an overload, or heat sensor on this fan, and tucked away the engine compartment is getting too hot, so the 'safety' is switching it off.

How about wiring it directly to a temporary completely independ battery. This will run it long enough to check the fan itself is ok, and not cutting out.

I'm assuming the voltage would have to drop very low to drop a solenoid. Think of a car headlights, they usually stay on when starting the car, despite the voltage dropping to say 10v.

I'm sure I may be corrected by an electrician, but it may give you a place to start.

 

[powerskipper]

Is the alternator not keeping consistent power requirements, sounds like something is reducing power at times, may be obvious and way off, but have you checked the belts, they mite be slipping, causing drop in voltage etc
/forums/images/graemlins/grin.gif

 

[halcyon]

Doubt it's run from starter motor, as it would be on full time, or only when starter motor is running.
Could be that they are picking up power for fan from starter motor perminant feed, ( via relay contacts ) and feeding relay coil from alternator warning light output. Thus you only run fan when engine is running.
You may be trying to feed the fan and relay coil from the alternator warning light output, thus at low RPM you do not have enough voltage to run the fan. As you increase rpm you have a larger output from field diodes, and thus fan runs.
Sorry but it's going to be a voltmeter and follow the cables job.
If the fan belts are a major issue, get a couple of small crocodile clips and two lengths of wire, fit clip were you want to measure, and the other to earth. You can then fit the other ends to voltmeter and start engine, checking voltage from a save distance. Then stop engine and move your cables to the next point.

Brian

 

[HeadMistress]

My WAG (keeping in mind that my professional expertise is plumbing, not electrical): the wire from the blower to the power source is inadequate.

When measuring the distance to determine the correct wire size, many people mistakenly fail to realize that it's the round trip distance, not the one-way distance, that determines the correct wire size....which often results in wiring too small for the load/distance.

If I'm right, no need to ship the wine across the pone. Just make sure to buy one that only gets better with age and save it till I can over and drink it with you. /forums/images/graemlins/smile.gif

 

[philip_stevens]

Just a thought, but is your engine compartment completely enclosed? If so, this could be why the blower is stopping at high revs - it may have an internal overheat switch, that is being overloaded when the blower is running and trying to blow against the engine sucking air in. Some of these motors do have internal overheat/overload protection to safeguard against overheat/fire.

At low revs, it can cope by the fact that not a lot of air is going into the engine - but at high revs, the engine is sucking like hell, and putting a reverse air load on the fan blades. Hence, high load, and high heat, resulting in the internal overheat trip (if it has one) opening until the motor has cooled down by the engine drawing in cool air.

Just a thought.

BTW, is the Yanmar diesel? If so, why do you need an bilge air blower? I thought blowers were mainly for petrol engined installations. Also, why do you need it running all the time?

If it is to supply air to the engine, maybe (and I am not being sarcastic) could it be reverse flowing? Blowing out when it should be sucking in.

 

[jfkal]

Couple of things.

1. Check the wire size, could be too small
2. Do not wire from starter motor I supect you are drawing "through" the starter motor against alternator output. Hence the higher the alternator voltage the lower you get for the blower /forums/images/graemlins/frown.gif
3. Wire through a relay which "sits" on the "ignition or acc." position of the starter key (I know you have a diesel but the key has that extra step anyway). Advantage is that you can keep the blower running after the engine is off (provided you can tolerate the beeeeeeeeeeeeeeeep from the panel) cooling the compartment.
4. Someone asked why a blower? Cooler air is more dense --> more oxygen -----> more engine oooomph.
5. I have a 3GM as well and done the wiring as I said.

PM me for address for wine /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

 

[IanR]

All,

Thank you for the advice and tips, when I get a chance I will be down to the boat for another episode and the advice that wins the day wins the wine.

Watch this space...

I love sailing,,,, I despise engines.......

 

[ytd]

since the loss of power is revs dependent, have you tried tightening all the earthing points - the alternator, starter , etc. I once had a charging problem at high revs on a Bukh motor that turned out to be an alternator mounting bolt that could be turned another half a turn.

 

[philip_stevens]

[ QUOTE ]
4. Someone asked why a blower? Cooler air is more dense --> more oxygen -----> more engine oooomph.

[/ QUOTE ]

I always thought a bilge blower was to rid the bilges of a build up of petrol fumes and/or butane gas spillage, before starting a petrol engine. Therefore I would assume that it is sucking from the bilge and/or the engine compartment - depleting/lowering air pressure from the engine compartment.

Is it a bilge blower or engine compartment cooler/blower?

If a bilge blower, then my previous comment stands. So what is it??

 

[HeadMistress]

A bilge blower does suck fumes out of the bilge...but there must be a source of fresh air to replace the air the blowers pull out. Which is one of the reasons why petrol powered boats have louvred vents on each side of the hull. The louvred vents--in pairs, one forward facing, the other facing aft on each side--also provide passive ventilation to the engine room while the boat is underway.

 

[philip_stevens]

Thanks Peggy,
all explained to a raggie, though what natural ventilation is there on Ian's sailing boat - I take it that it is a sailing boat, being as how the engine is only 23hp.

I still have the feeling that the fan is being overloaded when the engine is on fast revs. I may be, and probably am, wrong.

 

[IanR]

Wow its exciting seeing all this traffic, I am unworthy.

I haven't got back to the boat yet to continue the saga, however to answer some of the current questions.

Yes the engine bay is sealed except for 1 x 100 mm air pipe in and 1 x out, the out is connected to the blower which sucks air from the top of the engine bay. The outside connection is to the face of cockpit lockers where there is an air gap to let ventilation work. (The airgap is never sealed by any obvious means)

The in air pipre comes to the gearbox end of the engine bay.

The blower works somewhat hesitantly when the engine is on tickover, but does not when the revs build, It seems from recommendations, that I need to find out whether it is because of suction from the engine or drop in supply voltage

The engine is a 3GM30 and has a freshwater cooling system which has a heat exchanger, it is diesel and therefore I assume needs the blower one to drag in fresh air by pushing out the stale air. It does get very hot in there if the blower stops.

The wiring is the original wiring which appears to be of a reasonable gauge and of sound condition, I did check for resistance over the length and if it less than .2ohm. (Each wire so not return)

I also will be chacking upstream from the relay to look for loose connections on the back of the starter motor etc...

I live in hope of finding out the answer ASAP /forums/images/graemlins/confused.gif

 

[philip_stevens]

Keep us posted.

4 inch pipes, eh?? Sounds omimously like air. I've got a VP 2003 28hp, and on full chat, there is a lot of exhaust. So mucho exhaust wants mucho inlet air.

As I say, keep us posted on what you find.

If I may digress, I spent 25 years as an electrical officer on steam turbine containerships. We had to keep four or six (depending on what ship I was on) supply fans on full power when underway. When in port and the boiler was at minimum, only 2 fans were required, and we could put 2 others onto exhaust to keep the ER cooler for maintenance.

On one ship, half the fans failed coming up the Red Sea. The first instance was the boilers getting starved of air and consequently we had to slow down until we got the fans back online again. The switchboard for the fans was at the very top of the ER, and the digital thermometer the 1st Engineer took up with him registered 64degrees C where we were working - for about 10 minutes at a time.

So, what you could do, is reverse the flow of your bilge fan and make it supply the engine compartment, and pressurise it slightly - not allowing it to get too much pressure and blow fumes into the cabin. You may also find that the engine runs slightly cooler and more efficiently when on full power. When at idle, switch the fan off.