Aerowhatt
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Posts: 426
Joined: Wed Jan 28, 2015 1:52 pm

Re: Supplemental cooling for the charger.

Sat Jul 14, 2018 1:34 pm

Sure enough, Siai47's information is correct yet again. I moved my remote temp sensor to the return line of the coolant loop a few inches from the connection to the coolant tank in the back of the car. Under L2 charge it peaked at 113F or 33F above ambient. So we are cooling the components with what would be considered nice hot water coming out of one of our kitchen sink faucets. Of course it is worse if the ambient temperature is higher than my fortunate 80F garage is!

Also noticed that the radiator cooling fan only has a two wire connector. Which means that the low speed voltage is achieved somewhere else in the cars systems. It is not built into the fan motor :(

Realistically the radiator (with airflow) should be able to return coolant just a few degrees (<5F) above ambient air temperatures. I think a 25F to 30F reduction in operating temperature is likely worth the time and effort for a modification.

Aerowhatt
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

Aerowhatt
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Posts: 426
Joined: Wed Jan 28, 2015 1:52 pm

Re: Supplemental cooling for the charger.

Sat Jul 14, 2018 3:35 pm

I put 50 CFM worth of blower airflow through the condenser and radiator from the front. After an hour the coolant temperature stabilized down ~9F to 104.4. Removing the motor bay hood there was a lot of really hot air trapped in there. Feeling the inverter it was still too hot to hold on any surface (can't really reach the bottom).

I moved the blowers to the charger bay, blowing air over the top and across both sides, more or less. After an additional hour the coolant temperature stabilized at < 100F. The charger can be touched and held on any surface without discomfort. Given this rather unexpected result I'm going to go with two Nidec blowers connected to the 12V DC harness. By using a properly rated heat switch it will cool when needed and be off the rest of the time automatically. Mounting will be a bit tricky but looks workable.

Conclusions from these observations:

1. The OEM cooling strategy for the charger/DC-DC is underwhelming.
2. Increasing the cooling at the radiator provides some improvement.
3. Direct forced air cooling of the Aluminum case of the charger makes a big improvement. Not only is the case much, much cooler, but it being so, is allowing the components to dump so much heat to the case that the coolant temperature drops ~13F or more, The obvious conclusion from this observation is that so much heat is being pulled of the unit by air cooling the case, That even the fluid cooled plate at the bottom of the unit has significantly less heat to transfer to the coolant and the coolant stabilizes at < 100F

As soon as I get this mod fabricated and installed I will post pictures, etc., and recheck the coolant temperature steady state at L-1 and L-2 rates

Aerowhatt
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

JoeS
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Location: Los Altos Hills, California

Re: Supplemental cooling for the charger.

Wed Jul 18, 2018 8:27 am

I was shocked, I tell you, I was shocked, as up until now I had considered the engineering on our i-MiEV to be excellent. It simply never occurred to me that, with liquid cooling, there would be any thermal issues, and certainly did not expect high case temperatures. I had simply assumed that Mitsubishi had calculated that a radiator fan was unnecessary... DUH. I haven't removed the rear access cover in years, and I bet a layer or dust/dirt doesn't help the thermal situation either.

Aerowhatt, thank you for performing the measurements. Like I said, shocking! siai47, thank you for still keeping up with us and offering your wisdom.

Like Don, my first reaction was to go back to charging on L1 (120vac).

For the time being as a quick-and-dirty partial fix attempt in this summer heat, I've stuck a 120vac fan in front of the car at the radiator inlet and one underneath the back of the car aiming straight up to at least move some of the air back there. Edit: I activate both fans with the timer for the EVSE.

Aerowhatt, looking forward to seeing what you come up with.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

wmcbrine
Posts: 363
Joined: Wed Apr 29, 2015 10:26 am
Location: Laurel, MD
Contact: Website

Re: Supplemental cooling for the charger.

Wed Jul 18, 2018 4:28 pm

Don wrote:But, if not, recharging L1 at 12 amps (1440 watts) will cut your waste heat by more than half and it's a completely free option, costing you nothing and no mods needed.

L1 charging is less efficient, so there's a cost in terms of electricity. (I'm not sure how much.)

Aerowhatt
Gold Member
Posts: 426
Joined: Wed Jan 28, 2015 1:52 pm

Re: Supplemental cooling for the charger.

Wed Jul 18, 2018 5:23 pm

I have a prototype cooling blower mounted in my car and two charges monitored with it. First let's review.

First all of, the numbers are are based on my 80F ambient charging environment. It is reasonable to use these numbers adding or subtracting as needed depending on your ambient charging location temperatures.

As designed the OEM cooling system delivered the following results.

Under L-2 the case temperature peaked at 56F above ambient temp.
Under L-1 (12 amp) the case temperature peaked at 48F above ambient temp.
So charging L-1 only delivered a ~15% decrease in charger temperature rise.

Switching to coolant inlet temperature as the comparison metric.
Under L-2 OEM setup the inlet coolant temperature was 113F (33F above ambient)
With 50 CFM of ambient air blowing directly through the radiator this was reduced to 104.4F (charger case still too hot to hold on to)
With 25 CFM strategically blowing on the charger case, the case (nothing on the radiator) the coolant temp reduced to 99F (19F above ambient) (charger case easily held on all sides and top).

The prototype is a single Nidec Gama 30 blower strategically placed in the motor bay. As a prototype the the bracket is pretty ugly, but that's why we prototype. Nothing like doing it to show one what needs improved. Like the prototype bracket, the final version will require no drilling of the car whatsoever, and will be fairly easy to remove and reinstalled should a warranty trip to the dealer come up. Even with the hatch lid completely installed and the sound insulation, etc., plus all the junk I keep in the trunk :oops: . I'm getting the same temps as I did in the cover open - blower cooling the charger trials.

Funny how realizing your >$4,000 charger/DC-DC is running uncomfortably hot motivates one to get things done. I plain didn't want to charge again without a solution in place. Wife always get nervous when I'm working in the garage late into the night ;)

Aerowhatt
Last edited by Aerowhatt on Wed Jul 18, 2018 6:57 pm, edited 2 times in total.
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

wmcbrine
Posts: 363
Joined: Wed Apr 29, 2015 10:26 am
Location: Laurel, MD
Contact: Website

Re: Supplemental cooling for the charger.

Wed Jul 18, 2018 6:34 pm

JoeS wrote:I was shocked, I tell you, I was shocked, as up until now I had considered the engineering on our i-MiEV to be excellent. It simply never occurred to me that, with liquid cooling, there would be any thermal issues, and certainly did not expect high case temperatures.

I don't think it's been proven, yet, that there are thermal issues -- only that greater cooling is possible. But, what matters is what temperatures are in spec for the components, not whether they're hot to the human touch.

Aerowhatt
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Posts: 426
Joined: Wed Jan 28, 2015 1:52 pm

Re: Supplemental cooling for the charger.

Wed Jul 18, 2018 6:54 pm

wmcbrine wrote: I don't think it's been proven, yet, that there are thermal issues -- only that greater cooling is possible. But, what matters is what temperatures are in spec for the components, not whether they're hot to the human touch.


I've been charging EV's for clients for 18 years. Recommending and installing the gear to get the job done. Just my experience and opinion here. Manufactures spec their components to beat the competitions components. So specs are more often than not generous in the direction that OEM buyers like to see, to be competitive. The EV's on which I was able talk the owners into supplemental cooling for the chargers would get at least twice the MTBF (mean time between failures). They spent a lot less money in the long run too. All electronics work better and longer at lower temperatures IMO and experience. They always have and always will!

Imagine charging outdoors with 100F ambient temperature. Case temps would be 156F at L-2 rate. The case is always cooler than the components cranking out the heat (sometimes by 40F). I'm going with actively cooler since specs have always been off the mark for longevity in my rather extensive experience. The proof when it comes is too pricey in my estimation!

Aerowhatt
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

JoeS
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Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Supplemental cooling for the charger.

Thu Jul 19, 2018 8:48 am

Aerowhatt wrote:...Funny how realizing your >$4,000 charger/DC-DC is running uncomfortably hot motivates one to get things done. I plain didn't want to charge again without a solution in place. Wife always get nervous when I'm working in the garage late into the night ;)
Same here! :geek:

Regarding failure rates, one need to simply google "mtbf vs. temperature" for just about any type of electronics component and check out the graphs to see the dramatic component life decrease for increasing temperature. For semiconductors, it all goes back to maintaining as low a junction temperature as possible.

Without sitting in on the design reviews of each of our major subassemblies, we simply don't know to what depth each individual component was analyzed and what coordination existed between the circuit designers and mechanical engineers, especially from a thermal analysis and control standpoint. For example, different potting compounds can act as thermal conductors or thermal insulators - BIG difference! Liquid cooling normally implies that all significant power-dissipating components are tied into that heat exchanger, and I would have expected minimal contribution to cooling by the chassis. For reasons already ably discussed by Aerowhatt, I find both the lack of a temperature-activated electric fan in front of the radiator and the high chassis temperatures during charging to be disturbing.

Aerowhatt, what did you pick up as your fan's 12v power source, activated only during charging?
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

Aerowhatt
Gold Member
Posts: 426
Joined: Wed Jan 28, 2015 1:52 pm

Re: Supplemental cooling for the charger.

Thu Jul 19, 2018 10:02 am

JoeS wrote:Aerowhatt, what did you pick up as your fan's 12v power source, activated only during charging?


Right now it is temporary, separate 12 ah AGM. The DC to DC output is right there and easy to connect to. The negative will go to ground (likely to the bracket for the blower). Fuse (3 amp) right at the positive connection to the DC to DC post then to a surface temp switch on the opposite end of the charger case. It should turn on when the case on the leeward side gets to ~120F then off when it cools to ~110F. From what I'm seeing that should have it on only when charging.

I need to do two setups. One for each car, so I might make a jig for the bracket. If so, then it's a short step further to put together a kit that others could use (if there is enough interest). Even if it was slow to shut off in a very hot climate it wouldn't be much of an issue. These blowers are very efficient and only use 7 to 9 watts running.

Aerowhatt
2014 cool silver ES, acquired new 4/2015 (42.7ah at ~26K miles)
2014 Labrador Black Pearl ES, acquired new 3/2016 (41.5ah at ~15k miles)

JoeS
Site Moderator
Posts: 3556
Joined: Thu Dec 15, 2011 5:47 am
Location: Los Altos Hills, California

Re: Supplemental cooling for the charger.

Thu Jul 19, 2018 2:33 pm

Aerowhatt, glad to see your entrepreneurial spirit alive and well, and count me in for a couple of 'kits', if you decide to do it.

I haven't taken my front bumper off lately, but IIRC there was lots of room in there to place a fan. Too many other projects for me to play with this right now, and my external 120vac box fan is certainly least-effort for now.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

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