Alternator / engine room fan thermostat

[Molteni]

I'm particularly interested in cooling the alternator which can produce up to 60 Amps.

To this end we've recently fitted an engine room fan, to force air to circulate from the large cockpit locker.

Yesterday we finished a sail with a half hour motor with the alternator pushing out around 10 amps, and an IR thermometer showed the alternator casing to be 60 degrees C.

I'd like to install a thermostat which attaches to the alternator casing, and will "trigger" a relay to power the 5amp fan. This needs to be make-on-rise when the temperature of the metal casing reaches, say, 80 degrees C.

The engine room air temperature is not a concern, we just need to protect the alternator from overheat damage under heavy load. The fan is plumbed in (but not yet wired) to draw cooler cockpit locker air in close to the alternator.

Can anyone recommend an appropriate thermostat ?

Thanks in advance

Mike

 

[NormanS]

The biggest fan is the engine, which gulps in vast quantities of air. Why not just duct your engine room air inlet so that it directs air onto the alternator?

 

[Alex_Blackwood]

The biggest fan is the engine, which gulps in vast quantities of air. Why not just duct your engine room air inlet so that it directs air onto the alternator?

I think you are on "Overkill" I would suggest that all would be well without a fan. How does the air get into the cockpit locker?

 

[Molteni]

Air gets into the engine compartment (for combustion) via an inlet by the engine instrument panel in the cockpit. This air enters the engine compartment via the cockpit locker The system recently plumbed in effectively uses the large cockpit locker as a "heat sink", with the inlet to the engine compartment right by the alternator.

 

[Plum]

Air gets into the engine compartment (for combustion) via an inlet by the engine instrument panel in the cockpit. The system recently plumbed in effectively uses the large cockpit locker as a "heat sink", with the inlet to the engine compartment right by the alternator.

Then you have an excellent air flow over the alternator already which you are not likely to improve on. What makes you think 60 degrees is too hot for an alternator. Sounds ok to me.

www.solocoastalsailing.co.uk

 

[Molteni]

Then you have an excellent air flow over the alternator already which you are not likely to improve on. What makes you think 60 degrees is too hot for an alternator. Sounds ok to me.

www.solocoastalsailing.co.uk

The alternator could be running very hot while the engine is at low speed. At full load (close to 1kw?) the alternator could run at well over 60 degrees C requiring additional local cooling.

 

[Alex_Blackwood]

The alternator could be running very hot while the engine is at low speed. At full load (close to 1kw?) the alternator could run at well over 60 degrees C requiring additional local cooling.

I would be more worried about the air flow when you start storing in the locker and fill it up with all sorts of "Bits and Pieces" . Of course that will never happen, silly me! Seriously how often do you expect your alternator to run at 60 amps with insufficient air being pulled in by the engine?

 

[Molteni]

........Seriously how often do you expect your alternator to run at 60 amps with insufficient air being pulled in by the engine?

Just the once might be enough to destroy the alternator. I've seen 84amps on the meter, on what is effectively just a car alternator.

I'm looking for a bolt-on/clip-on thermostat for the alternator to power a relay for the fan. Any recommendations please?

 

[Alex_Blackwood]

Just the once would be enough to destroy the alternator.

I'm looking for a bolt-on/clip-on thermostat for the alternator to power a relay for the fan. Any recommendations please?

Try these.
https://www.digikey.co.uk/en/produc...ensors-thermostats-mechanical-industrial/1072

Thermostatic Switches, Temperature Control Switch | RS

 

[Molteni]

Try these.
https://www.digikey.co.uk/en/produc...ensors-thermostats-mechanical-industrial/1072

Brilliant, thanks. Looks like the 85 degree one will do the job, and is rated to power the 5A fan without needing a relay.

 

[Alex_Blackwood]

Brilliant, thanks. Looks like the 85 degree one will do the job, and is rated to power the 5A fan without needing a relay.

Double check that it is the correct operation i,e. Normally open and closes on rising temp. Other wise you will need the relay! The RS ones may be best.

 

[geem]

Just the once might be enough to destroy the alternator. I've seen 84amps on the meter, on what is effectively just a car alternator.

I'm looking for a bolt-on/clip-on thermostat for the alternator to power a relay for the fan. Any recommendations please?

Just have the fan on a switch. Start engine turn on fan. Stop engine turn off fan. It's what we have been doing for ever.
Most electrical components are rated for about 40degC unless rated for high temperature.

 

[Spirit (of Glenans)]

Just have the fan on a switch. Start engine turn on fan. Stop engine turn off fan. It's what we have been doing for ever.
Most electrical components are rated for about 40degC unless rated for high temperature.

Or wire the fan into the "ignition" switch. One less component to go wrong.

 

[roaringgirl]

Normally, the alternator itself has a fan on it that spins with the pulley. Our Balmar external alternator regulator can be programmed to reduce alternator output as temperature rises.

 

[ChromeDome]

Alternators can and will get hot - well over 60 C. However, if it gets extremely hot (frying pan class) you need to check your batteries and charge regulator.

 

[Molteni]

Normally, the alternator itself has a fan on it that spins with the pulley. Our Balmar external alternator regulator can be programmed to reduce alternator output as temperature rises.

Strangely the pulley on my Prestolite has "radial" fan blades rather than those angled to draw air into the alternator casing.

Alternators can and will get hot - well over 60 C. However, if it gets extremely hot (frying pan class) you need to check your batteries and charge regulator.

This was my concern, especially as the alternator would often be working much harder than a typical car unit. Mine was at 60 degrees with just short usage at 10 Amps and reducing

 

[geem]

Strangely the pulley on my Prestolite has "radial" fan blades rather than those angled to draw air into the alternator casing.
This was my concern, especially as the alternator would often be working much harder than a typical car unit. Mine was at 60 degrees with just short usage at 10 Amps and reducing

From my experience, running a good engine room extract system in the Tropics results in an engine room temperature of 40degC. Without engine room extract our engine room would reach 60degC. Once the engine is hot it creates a high radiant temperature within the space meaning anything else within that space a absorbing the heat. Since the alternator is very close the the engine it will see a high temperature regardless of how much work it is doing if you are running for a long enough period for the engine to get to full temperature. Most alternators run quite happily at 80 degC. If it has its own fan it should easily stay below this temperature if it is a standard unit designed for marine use. Has the alternator been tampered with or modified in any way?

 

[Molteni]

The alternator is a nearly new Prestolite rated at 90 Amps. Unmodified except that I've fitted a regulator with the negative field wire to connect to an external Sterling regulator. We were surprised to briefly see 84 Amps in the summer after starting the engine with heavily discharged batteries (600Ah worth discharged to 60% capacity.
The pre-existing ducting to the engine compartment allows air in from the opposite end to the alternator. We've hacked a hole for air to more directly enter near to the alternator and installed the (presently unconnected) fan to extract air from the end away from the alternator. There's little space to place the fan anywhere else.

 

[superheat6k]

As long as your alternator surface is below 100oC I wouldn't worry too much. The windings will be sound internally to over 120oC. I certainly would not be wasting 5a of its output on randomly blasting air over it - they do have their own fan impellers, and will work in warm engine bays to at least 60oC local ambient.

 

[Ian_Edwards]

12V Temperature Controller Switch with Probe 20A Thermostat Control -UK | eBay

I bought 3 of these to control fans, which I use to ventilate, the 5kVA inverter, housed under the nav table, the rectifier/inverter on the Whisper Power generator, and to provide additional airflow over the fridge compressor.
All these units are housed behind panels which don't allow a lot of ventilation. The fans extract air from the bilge and the hot air escapes through louvered vents.
They've been installed for over a year now, and are "fit and forget".
They have a temperature probe on about 700mm of wire, which I taped to an appropriate bit of the kit which gets hot.
You can use them to control heaters or cooling fans.
Setting them up was easy, because you can see the temperature at the probe.
And they are remarkable cheap.