Alternator cooling

[frahkn]

My alternators are cooled by drawing bilge air past them through a conduit using a 'DetMar 7-5-4' in line blower.

This has failed and I need to replace it.

I there a UK supplier or is there an alternative which you could recommend?

On line there seems to be a very great price range which makes me doubtful about getting a replacement at random.

Thanks.

Frank.

[Tony Brooks]

I don't know what is special about DetMar so try googling for a 3" bilge blower. I suspect you will find a great choice starting at £13 on Ebay and then upwards from marine outlets. As long as the throughput is the same or better I do not see the brand matters

[WotEver]

Google suggests 158cfm. They're very cheap - about $27 US. 

[Alan de Enfield]

1 hour ago, frahkn said:

My alternators are cooled by drawing bilge air past them through a conduit using a 'DetMar 7-5-4' in line blower

You say "drawing air" (ie 'sucking') but then mention 'blower'.

Before replacing it may be worth just confirming if you are looking for a 'sucker' or a 'blower'

[WotEver]

20 minutes ago, WotEver said:

Google suggests 158cfm.

Which is roughly 4500 L/min if you're looking for an equivalent. 

19 minutes ago, Alan de Enfield said:

You say "drawing air" (ie 'sucking') but then mention 'blower'.

Before replacing it may be worth just confirming if you are looking for a 'sucker' or a 'blower'

The manufacturer calls them 'bilge blowers'. They're just a fan in a tube. 

[frahkn]

26 minutes ago, Alan de Enfield said:

You say "drawing air" (ie 'sucking') but then mention 'blower'.

Before replacing it may be worth just confirming if you are looking for a 'sucker' or a 'blower'

Tubular flexible conduit, about 2 meters long, 3" diameter, cut into two lengths.

Top half fixed to hole in roof (deck head?), this hole is covered by a mushroom. The bottom half wrapped in heat-proof lagging and laid along engine with open end near alternators.

In the middle (i.e. between the two halves) connected to both, is the DetMar. This is fixed to a bulkhead for support and the conduit is held on with cable ties. Connected via fuse and switch, to the 12 volt supply. It sucks air from the bilge, over the alternators and shoves it out the roof. If you put it in upside down it would route the air in the opposite direction.

So I am happy with a sucker or a blower.

How can you help me?

 

WotEver put it much more succinctly while I was typing.

Edited June 21, 2017 by frahkn

[OldGoat]

Seems a lot of effort? Is there something 'special' in the alternator setup? Such as running a cheap alternator at twice it's normal speed.

I got paranoid when I built my boat and put two 10" fans in front of the engine and two switchable exhaust fans in the rear deck for hot days. I never use the latter and the others I run at half speed. Not had any problems, but the alternators are bus and lorry type.

Anyway that wasn't your question.

To change what the unit does - just turn it round - one end blow and the other sucks. IMO blowing is better than sucking as it takes more effort to pull than it does to push.

 

[Alan de Enfield]

48 minutes ago, WotEver said:

Which is roughly 4500 L/min if you're looking for an equivalent. 

The manufacturer calls them 'bilge blowers'. They're just a fan in a tube. 

I know what the are - I have two 'bilge blowers' in each of my boats.

I was simply asking the OP if he needed a 'sucker' or  'blower' - it appears that he needs a 'sucker' to evacuate the hot air from the engine room, rather than a blower to blow cold air over the alternator.

[WotEver]

Just now, Alan de Enfield said:

I know what the are - I have two 'bilge blowers' in each of my boats.

I was simply asking the OP if he needed a 'sucker' or  'blower' - it appears that he needs a 'sucker' to evacuate the hot air from the engine room, rather than a blower to blow cold air over the alternator.

Surely if it's blowing it's also sucking, from the other end. 

[Alan de Enfield]

3 minutes ago, WotEver said:

Surely if it's blowing it's also sucking, from the other end. 

Indeed - but as with any propeller it is important to get the 'right one' and install it the 'right way'.

[mross]

A blower will probably shift more air as it is likely cooler and denser than the air a suction fan would shift.  Alternator fans are radial, not like propellers, which are axial.  It's worth noting that the blades point backwards.  Instinct might suggest otherwise.

[Alan de Enfield]

5 minutes ago, mross said:

Alternator fans are radial, not like propellers

But we are not talking about the alternator fan - we are talking about bilge-blowers being used to give additional alternator cooling.

[frahkn]

32 minutes ago, OldGoat said:

Seems a lot of effort? Is there something 'special' in the alternator setup? Such as running a cheap alternator at twice it's normal speed.

I got paranoid when I built my boat and put two 10" fans in front of the engine and two switchable exhaust fans in the rear deck for hot days. I never use the latter and the others I run at half speed. Not had any problems, but the alternators are bus and lorry type.

Anyway that wasn't your question.

To change what the unit does - just turn it round - one end blow and the other sucks. IMO blowing is better than sucking as it takes more effort to pull than it does to push.

 

There is nothing special about the setup, just a Beta 43 with the usual alternators. What is special (insane) is that the engine is fully cocooned and is in the bathroom at the end of the bath!!!

My boat (a 70' Orion tug) has four external passive fittings designed to take air in at the front, pass through the bilge, and exit from the back. This seems to work so long as the intakes are kept clear.

So cool air from the bilge is pulled across the alternators and exits (by now quite warm) through a mushroom on the roof.

I will have to get a new one so I may experiment with putting it the other way round just to see. The problem that I have an infra-red heat measuring 'thing' but to use it the cocoon has to be off - thus changing the experimental conditions.

Frank.

[OldGoat]

42 minutes ago, frahkn said:

There is nothing special about the setup, just a Beta 43 with the usual alternators. What is special (insane) is that the engine is fully cocooned and is in the bathroom at the end of the bath!!!

My boat (a 70' Orion tug) has four external passive fittings designed to take air in at the front, pass through the bilge, and exit from the back. This seems to work so long as the intakes are kept clear.

So cool air from the bilge is pulled across the alternators and exits (by now quite warm) through a mushroom on the roof.

I will have to get a new one so I may experiment with putting it the other way round just to see. The problem that I have an infra-red heat measuring 'thing' but to use it the cocoon has to be off - thus changing the experimental conditions.

Frank.

How very interesting - it all now makes sense.

Must be a very quiet boat.

If I may ask - what's the drive? Hydraulic / shaft / electric?

We once hired a boat from Teddesley with a Ford XLD mounted well forward of where a proper engine room would be -but it had a raise floor to accommodate the propshaft. Lovel and quiet.

[Chewbacka]

Just a word of caution - some of the cheap bilge blowers you can get on ebay are designed to extract petrol vapours etc before attempting an engine start.  So are only designed for intermittent use.  Sounds like you need a continuously rated blower.

[cuthound]

Hi Frank,

How about using one or more USB temperature logger sensor,  like this one to measure the temperature in side the cocoon?

https://www.google.co.uk/search?q=tinytalk+temperature+monitors&oq=tinytalk+temperature+monitors&aqs=chrome..69i57.12425j0j4&client=tablet-android-samsung&sourceid=chrome-mobile&ie=UTF-8#xxri=1

Tape in place, do your experiments and then connect to a computer to see the details of temperatures logged.

[frahkn]

5 hours ago, OldGoat said:

How very interesting - it all now makes sense.

Must be a very quiet boat.

If I may ask - what's the drive? Hydraulic / shaft / electric?

We once hired a boat from Teddesley with a Ford XLD mounted well forward of where a proper engine room would be -but it had a raise floor to accommodate the propshaft. Lovel and quiet.

The engine is about 12' forward of the prop. and set to one side of the boat.

The drive is a three part shaft with "universal" type ends on each section. My surveyor was concerned by the likely life of this setup (apparently the angles between the sections exceed that recommended) but it has survived four years of my ownership with no problems yet.

The engine is very quiet - only one Thames lock-keeper noticed it was on between Oxford and Brentford; but this means you can hear drive from noise under the steerer's feet. At low revs this sounds like a bag of screws in a tumble dryer. 

3 hours ago, cuthound said:

Hi Frank,

How about using one or more USB temperature logger sensor,  like this one to measure the temperature in side the cocoon?

https://www.google.co.uk/search?q=tinytalk+temperature+monitors&oq=tinytalk+temperature+monitors&aqs=chrome..69i57.12425j0j4&client=tablet-android-samsung&sourceid=chrome-mobile&ie=UTF-8#xxri=1

Tape in place, do your experiments and then connect to a computer to see the details of temperatures logged.

I might just give this a try.

[sans allumette]

These China-made aquarium thermometers are cheap as chips at just over £1 each. Bought several to check temps on my domestic CH pipework. The downside is you have to write the temperatures down somewhere. No recording function!

http://www.ebay.co.uk/itm/Aquarium-Fish-Tank-Thermometer-Water-Temperature-Gauge-LCD-Digital-Thermometer-/322393560172?hash=item4b1027546c:g:DB4AAMXQWzNSeKv~