Keel cooling design for electric inboard

What is your filler? Usually copper based saltwater heat exchangers use rolled connections, but there are perferred fillers. You want a filler that is slightly cathodic to the tubes and headsheets.

 

Thanks. Any specific US designations of solders good for saltwater?

 

Copper pipes handle higher pressures than what the cooling system will have. I don't understand why you equate easy to find and cheap with unreliability.

 

Silver solder would be my preferred one. The old tin/lead was not as strong but impossible to get as far as I know.

 

If it is all copper, then 50 50 lead tin is the perfered. Kinda hard to find as gonzo says becasue it cannot be used in potable water systems, but still available for this application and stained glass frames.

 

It's about the design, not the material.
The design imply welding or brazing, flanges and potentially 90° fittings.

 

You can use crimping, compression fittings, and bending the pipes too. You were talking about welding other materials, so what makes copper a problem?

 

That seem to me a good summary of lack or reliability I'm talking about.
It's not simple piping under the sink, it's piping underwater who can cause highly problematic problems to boat or motor is something go wrong.

I will still consider copper as the cooler can be way smaller than with SS316 cause heat transfer capability is something 25 time higher . Can worth the extra material cost.

 

I may be missing something. How are you fabricating a cooler out of stainless without welding, elbows or connections, as opposed at what copper would?

 

I don't. You see first post of this thread, right?
Simply that SS316 is way stronger than copper. So more reliable in this cooler application.

 

You need to design for at least 10,00o watts of heat dissipation. I don't know where you got your original numbers from. If you are assuming a big reduction in power, fine, but the efficiency goes way down. 92.5% efficiency at 147 horse power is more than 8kW heat rejection. This doesn't go down proportionally to power reduction. It goes down some, but not a lot. Coolant flow is listed at 7 l/min. Heat capacity of a 50/50 glycol mix is about 3.5 kJ/l. Converting to watt-minutes means the exchanger would yield about 12kW of heat rejection over a 30 C temp drop - say 80C in and 50 C out - at 7 l/min. The motor's max inlet temp allowed is 55 C. That's what you need to design the cooler around. There are several different Leaf motors and converters, but the differences aren't huge.

 

Really nice summary philSweet.
The unknow variable from you is I plan to use Leaf motor at 60V with peak power around 15-20 hp.

at 150 hp, right. So 1000W at 15hp seem right.

 

Uummmmmmm! Let think outside of the box a minute.
Copper is so conductive when compared to SS316 that a simple 3''x1.5'' (4,5 square inch) copper area could eject as much heat into the water than 125 square inch stainless steel cooler.
So, what about simply glue/fix a 1/8'' copper plate in a 3x1.5'' holes in the hull?

This thin 1/8'' plate is flush to the exterior hull the coolant touch this plate to move heat from motor to water.
In case of failure, motor coolant can flow inside the boat, but normally there will never have salt water intrusion.
In any case, the hole in the hull is ''small''.
I design rectangular shape, but round could be done.
Advice are welcome.

 

Electric motors and controllers reject heat mostly as a function of current, not voltage. A crude way to estimate heat rejection is to take the ratio of controller current that you are designing for and compare that to the rated current of a full voltage Leaf setup. It won't be linear with respect to power.

 

You are absolutely right.
And it's why I've estimate heat lost at 300-600W during cruising (at 3 to 6 kW, so around 70 to 150 phase Amps) and up to a max of 1500W for few minutes (at 16 kW and around 280 phase Amps).

Anyhow, I'm designing cooler to eject 5000W with a 50° temperature differential between coolant (80°C) and water(30°C).
That way, it's seem unlikely that I couldn't reach my cooling need goal.