Alternator Cooling

[GordMay]

Application & Installation Guide: “Engine Room Ventilation” ~ by Caterpillar

“... The primary aspects of a properly designed engine room ventilation system are cooling air and combustion air ...

... Approximate consumption of combustion air for a diesel engine is 0.1 m3 of air/min/brake kW (2.5 ft3 of air/min/bhp*) produced ...”

Much more ➥ http://s7d2.scene7.com/is/content/Ca...13-53120-44971

* 2.5 cfm per HP

[MWGDVC]

I have seen plastic back covers for the alternators of some cars that incorporated duct hose provisions, allowing a forced fresh cooling air source to be provided. In automotive applications, typically hose routed to a NACA duct under the vehicle. Think some BMWs, 928 Porsche, some of the mid engine Ferraris. Perhaps a replacement cover could be obtained for a Bosch alternator intended for one of these applications, and modified/adapted.

[AKA-None]

If you go with external rectifiers you might want to consider Ducted heat sink

[jfwg]

Before addiing a grate in front of the engine, I would think about what would happen if there was a fire in the engine compartment. Best practice is a fireport (so you don't have to open up the engine compartment to attack the fire) with a CO2 extinquisher (so you don't have to clean all that chemical off your engine before you start repairs... Just a thought...

[CaptainRivet]

Originally Posted by sailingharry

So I have a pair of Powerline alternators on my 4JH2E -- a 120 and a 150. They cheerfully put out a total well over 200A, and will do that for an hour or more. Unfortunately, they are showing heat damage, and I've sent them off for a preemptive rebuild. I want to make them run cooler.


First thing, I'm going to dive into the load management on the external regulators. But really, my problem isn't too much current (I WANT that!), it's too much heat. Reducing load is a reaction, not a solution.


First, we know that "high output small frame alternator" is an oxymoron. But it's a sailboat, and a big frame won't fit. And neither will a cooling system! There is not room anywhere to run ducts from a blower to the alternators.


I just had an idea. My engine room is moderately air tight (although fully connected to the bilge going forward). What if I mount a 250CFM Jabsco blower on the back bulkhead of the engine room, routed up to the deck vent (this would replace the useless little inline RULE in a dryer duct laying in the bilge). Then, mount a 4x12 floor register (like your home heating system) in the companionway stairs? This would put the register about 6" in front of the alternators. The blower would extract hot air from the engine room, and a fair amount of the makeup air would flow through the register, right at the alternators. Sure, the blower draws like 15A, but if it allows my alternators to run at 10% more capacity, I'd be ahead.


Would this actually get results? Or would I draw so much air from all those little engine room leaks that there wouldn't be much effect? Of course, air flow in general wouldn't be a bad thing for ambient temperatures. Are there any safety type hazards I'm missing in this?

Your alternators can safely output around 50% of their rating when! cooled properly. So its 60A+75A=135A and not the 200A you pull.
You need to scale down amps AND need to improve cooling and you maybe can go to 150A but never 200A if they should surive long.

[Wild Geese]

Out of interest what RPMs do the alternators turn at?

We have a single Powerline 120 amp alternator that never puts out more than 70 amps even when brand new. Heat was one of the questions the mechanic asked about and our fresh air input to the engine room was rerouted so the 4 inch diameter air intake hose exited at the alternator for maximum fresh cool air to the alternator to make sure.

RPM was the next question. Looking at the Powerline alternator power curve one of the reasons we can’t make the 120 is our engine does not turn fast enough. Our cruise power is 2600 RPM max and according to the alternator power vs rpm chart it can’t get more than 70 amps unless we were to take the engine to red line. Even then our red line RPM is 3200.

Is there a chance your engine doesn’t turn the alternators fast enough for the full power?

Happy sailing!

[CaptainRivet]

Originally Posted by Wild Geese

Out of interest what RPMs do the alternators turn at?

We have a single Powerline 120 amp alternator that never puts out more than 70 amps even when brand new. Heat was one of the questions the mechanic asked about and our fresh air input to the engine room was rerouted so the 4 inch diameter air intake hose exited at the alternator for maximum fresh cool air to the alternator to make sure.

RPM was the next question. Looking at the Powerline alternator power curve one of the reasons we can’t make the 120 is our engine does not turn fast enough. Our cruise power is 2600 RPM max and according to the alternator power vs rpm chart it can’t get more than 70 amps unless we were to take the engine to red line. Even then our red line RPM is 3200.

Is there a chance your engine doesn’t turn the alternators fast enough for the full power?

Happy sailing!

this is properly set up as when your engine runs redline (eg motoring of a lee shore in storm) your alternator is not running outside its specs and causing problems. Changing the gearing ratio here is fatal and not the right thing to do as you would need to massivly change the ratio to have significant improvements and in redline it will be way out of spec causing problems when you defintily don't want them (you never want but when running redline its already an emergency in most cases).


You actually describied one reason why only 50% of rating is save because these alternators are mostly truck ones and the power to rpm curve not optimum. only a heavy duty and very beefy alternator is able to pull his rating at 1500 or 2000rpm or even idle. And with Lithium you have to spec everything to idle to be save.

[StoneCrab]

How about directing the engine air intake through a duct which starts at the backside of the alternator?

With 250 cfm going through the engine, that is a huge air pump, just have that air passing through the alternator first. I don't have the installation fleshed out but if you got creative with some sheet metal, you could accomplish two things, air flow and shield the alternator from radiated engine heat.

To get the shielding built, find a local metal shaping club. These guys work on antique cars and are very skilled at shaping metal to very close tolerances. It might be a fun project for the right guy.

On my boat the Jabsco fans create more noise than the engine. I hate those fans. Just say'n.... the marine community needs Dyson to design some fans for boats that are silent.... or at least run at less than industrial noise levels.

[captstu]

Hi,

From the looks of your photo, your auxiliary alternator is driven by a single belt off an auxiliary pulley on the engine???

I had the same setup on twin 3GM35F engines - for a total of 510 Amps that drove a 1200 Ah battery bank, a 3Kw alternator and an air conditioner and washer/dryer.

Setup was very HOT - even after adding an auxiliary input and output blower to each engine. It ate duel heavy duty belts - next time I'll get tooth belts.

After 5,000 engine hours, I had used 2 alternators plus 1 OE 55 A alternator and - -

Both engines needed a zero tie rebuild, cracked pistons scored shafts, worn out bearings, ad - well $2200 worth of parts.

Still cheaper, quieter and far better that a generator to run the load.

[sailor1026]

You can do several things:
Direct incoming cooler air onto the alternators - a forced fan air supply is best.

Program the alternator regulator to dial back the amount of power generated so that the alternators don't overheat. Use an IR thermometer to check case temperatures and keep them below 200F. It's best to use a remote alternator sensor so the regulator continuously takes into account the temperature. The Wakespeed regulator has this capability. It's expensive and is the best regulator out there (I got to review the early versions).

Move the heat dissipated by the diodes to an external system to keep the heat away from the alternator windings (recommended by others on this thread). I recommend a solution from Mark Grasser (https://markgrasser.com/). He also has a regulator with alternator temp sensor and battery temp sensor.

[jr_spyder]

Interesting thread.

No matter what you do for cooling the alternators I’d think you’d want external regulators that have temp sensing for the alts that protect them when you’re past their limits. I’m not familiar with what you are using for regulators, but I installed Balmar MC-614 regulators as part of my migration from agm to lifepo4 batteries and really like all their features for maximizing output (my goal, like yours), using the right charging profile, and protecting the alternators (also Balmar). No guess work and peace of mind.

[CaptainRivet]

Best solution stack as much brand highest spec bifacial solar panels as you can and job done. clean, quiet, nearly maintenance free energy with victron mppts and you are mainly set. Alternator is just backup.

[CaptainRivet]

Move the diodes away from alternator is the most efficent way to reduce alternator temps without reducing output. Forget the rest of cooling stuff except when you have a cramped and badly ventilated engine room.

[Mauruuru]

The proper way would be to add both inlet and outlet air from outside the cabin. Route incoming ambient air over the area you are trying to cool and take exhaust from take exhaust from area across the engine room to maximize benefit.

[bcboomer]

Originally Posted by hjohnson

I’ll actually have 460Ahr of LiFePO4.

But that said, the alternator is going to be controlled by a Wakespeed WS500, so I can derate the alternator as required. My use case is primarily long weekend getaways, with the occasional 7 to 8 day trip.

The plan is to Leave the dock with a fully charged battery, and supplement with the engine as a range extender. I don’t expect the engine to bring the battery back up to full charge except on very long motor runs (say motoring up/down Jervis Inlet).

The Wakespeed is the only regulator on the market that actually measures the alternator output correctly so that is a great step. Before you spend a bunch on rebuilding and remoting your diodes take a look at the alternators from All-Tek in Alberta. They are industrial units and really reasonably priced. I have their 200 amp brushless small frame that is happy generating 180 amps. You could get a smaller one or dial it down until you get more power.