Inverter Temperature - Level 2 Charging

[Nekota]

I placed a data logging device to measure temperature on top of the inverter cover just under the brake fluid reservoir. Charging was started at 1AM with Level 2 and charge stopped at 80% . The LEAF is driven 30 to 40 miles for commuting. The primary heat source seems to be from charging or the radiator is very effective at cooling the moving vehicle. The background temperature is dominated by the solar heating of the car during the day and some small dips in temperature when the LEAF is driven due to the cool down or moving air around the inverter when the LEAF is in motion.

The input power from the EVSE (AV model) is about 3800 W so the charger has to dissipate the 500 W which apparently goes into the cooling system which is shared between the charger, inverter and motor. Since the vehicle is stationary during charging the radiator does not provide much cooling until fans turn on when the temperature gets high enough. These charges are for 2 to 3 hours to recover the charge to 80%.

LEAFInverterTemp

It took several edits to get the Flickr image working.

 

[Stanton]

Very interesting. Let me see if I understand: there's almost more heat generated by just "sitting in the sun" than the actual charging process? Of course, that's dependent on where you placed the temp sensor.

 

[TonyWilliams]

It seems odd that they would waste the money and weight on a cooling system that doesn't really seem necessary. A 20-30 degree F delta on temperature at the inverter might mean something completely different at the charger, however.

Is the liquid cooling because the charger is hiding behind the back seat with no ambient cooling air? Or just because they have liquid cooling for the AC propulsion motor, and just figured, sure, why not?

 

[ecoobsessive]

This is very interesting; thanks for posting. What's the ambient temp. when it's 1) charging and 2) outside in the sun?

 

[Herm]

The geek in me would love to know the charger efficiency (not counting the pumps and fans), probably around 92% which is standard with modern large transformerless AC-DC power supplies.. the need for active cooling may be due to places like Death Valley or the location of the charger in the back of the car. I really would love to get rid of liquid cooling.

AC Propulsion patented (IIRC) double tasking the 3 phase inverter used to drive the motor as the high power battery charger also .. I suspect this may become a trend in the future to lower cost when you have large batteries to charge.

Edit: I doubt you can avoid liquid cooling of the 80kw inverter.. perhaps in a decade as technology improves.

 

[gbarry42]

It seems odd that they would waste the money and weight on a cooling system that doesn't really seem necessary.

A few off-the-cuff remarks. If it looks like the cooling system isn't needed, it may be an indication that it's doing its job well. Also a sensor on the radiator would show how much heat is appearing there instead of at the point he measured.

Another thing we can see in the graph is how it cools in ambient (the daytime curve) vs. with the cooling system active (after the nighttime charge, if I'm deducing this right). As well as how fast it heats up under charge. Imagine where that curve could go (at 3 AM) without a cooling system and a longer charge time.

 

[planet4ever]

I seem to be the only worry-wart on the board on this subject, but my first reaction was, 'If there is that much of a spike with a 3.3 kW charger, what would it be like with a 6.6kW charger?'

Ray

 

[Nekota]

Very interesting. Let me see if I understand: there's almost more heat generated by just "sitting in the sun" than the actual charging process? Of course, that's dependent on where you placed the temp sensor.

The car lives outside in Sunnyvale and gets direct sunlight in the morning and when parked at work until about 3PM. I think most of the daytime temperature rise is from the "hot hood" that heats the trapped air under the hood. The sensor is placed under the brake fluid bracket and on top of the inverter. Cars get very hot by sitting in the sun and the metal parts in direct sunlight can reach 150F on a hot day.

 

[Nekota]

This is very interesting; thanks for posting. What's the ambient temp. when it's 1) charging and 2) outside in the sun?

The ambient temperature when the vehicle is charging is 65 to 70 degrees with the vehicle sitting outside. The temperature doesn't drop much more than 65 degrees in Sunnyvale in July. The temperature during the day last week (11-16) was in the mid 70's but inside the car at noon it's very warm.

 

[Nekota]

I seem to be the only worry-wart on the board on this subject, but my first reaction was, 'If there is that much of a spike with a 3.3 kW charger, what would it be like with a 6.6kW charger?'

Ray

Since the charger is part of the cooling loop and apparently only the circulation pump is running to dissipate the 500 to 600 watts of heat from the charger, doubling this to 1000 to 1500 watts may increase the temperature to the point where the fans turn on. The cooling system seems to be much larger than needed to cool the charging system so I would not worry about having a 6.6KW charger with this design. I may have to do some charging during the day to see if I can get the radiator fans to turn on.

 

[Nekota]

It seems odd that they would waste the money and weight on a cooling system that doesn't really seem necessary.

A few off-the-cuff remarks. If it looks like the cooling system isn't needed, it may be an indication that it's doing its job well. Also a sensor on the radiator would show how much heat is appearing there instead of at the point he measured.

Another thing we can see in the graph is how it cools in ambient (the daytime curve) vs. with the cooling system active (after the nighttime charge, if I'm deducing this right). As well as how fast it heats up under charge. Imagine where that curve could go (at 3 AM) without a cooling system and a longer charge time.

I agree with the observation of the cooling system is doing its job well and will look at some place to attach the recording sensor to a place closer to the fluid - e.g. radiator. But with the coolant pump running, I expect all the loop elements will have the same 'water' temperature unless the case of the inverter is not thermally "well connected" to the coolant.

 

[JasonT]

I swear, the longer I read this forum the dumber I realize I am. I am confused by this whole thread which is making me realize I do not truly understand how my Leaf works. If this is steering the thread off topic, let me know and I can start a new thread.

We're talking about three things here - the inverter, the charger, and the cooling system. Here WAS my understanding of these things:
-Cooling system - goes a couple of places, but biggest need is for the charger
-Inverter - the unit under the hood with the fake add-on to make it look like an engine. This unit takes the DC from the traction pack and turns it into the AC for the motor
-Charger - a "hidden" unit in the back where the "hump" is. This unit takes the AC from an EVSE and turns it into DC to charge the battery.

I must have this wrong, otherwise why would it matter what the temperature of the inverter was while charging? If someone could set me straight I would appreciate it.

 

[garygid]

You got it almost right, just slightly incomplete.

Add the Electric Motor component (hidden down under the Inverter), for Motor, Inverter, and Charger, all cooled by the same system. Two other related components are the Radiator, and the coolant pump(s) that run when the LEAF wants to circulate cooling fluid, which is low (no) pressure, unlike the fluid in ICE cars.

Then, the main cooling needs are for the Inverter AND Motor during Driving, especially up long hills and other high-power uses.

During Charging, when the Charger in the rear is generating (only a modest amount of) heat, the same liquid-cooling system circulates fluid to get the heat out of that confined space and up to the Radiator. In this mode, the temperature rise over ambient is rarely more than a few degrees, but the Chager gets critical cooling.

Does that help?

 

[TimLee]

You got it almost right, just slightly incomplete.

Add the Electric Motor component (hidden down under the Inverter), for Motor, Inverter, and Charger, all cooled by the same system. Two other related components are the Radiator, and the coolant pump(s) that run when the LEAF wants to circulate cooling fluid, which is low (no) pressure, unlike the fluid in ICE cars.

Then, the main cooling needs are for the Inverter AND Motor during Driving, especially up long hills and other high-power uses.

During Charging, when the Charger in the rear is generating (only a modest amount of) heat, the same liquid-cooling system circulates fluid to get the heat out of that confined space and up to the Radiator. In this mode, the temperature rise over ambient is rarely more than a few degrees, but the Chager gets critical cooling.

Does that help?

The temperature that has been monitored and recorded is inverter temperature. But it is indirectly a measurement of cooling fluid temperature because coolant is being circulated through the inverter by the coolant pump.
The only inaccuracy in your summary is that the data graphed clearly shows that the heat being picked up from the inefficiencies of the charger result in an ~20F rise in coolant temperature for the 2 to 3 hours of charging back to 80% charge level.

 

[garygid]

Was there any other heat source during the charging experiment?

My tests were indoors, overnight, in cool ambient conditions.

I could just barely detect any extra warmth by hand, comparing with the Heater "coolant" (in the front, driver's side).

So, the graph seems to show more temperature rise than I "experienced", but my "not-much" or "almost-undetectable-by-hand" experience was not well instrumented.

Had I seen a 20-degree rise in 2 hours, I would have probably dismissed the issue as "insignigicant". One wonders what an 8-hour charge would be like. If it is going up something like 10 degrees per hour, how high will it get after 7 hours?

 

[JasonT]

Does that help?

Yes, it does

The temperature that has been monitored and recorded is inverter temperature. But it is indirectly a measurement of cooling fluid temperature because coolant is being circulated through the inverter by the coolant pump.

Emphasis mine

Ah, that is what I wasn't getting - why measure the inverter when the charger is what is making the heat. That's what made me think I didn't understand either the Leaf system or the experiment. Thanks for the clarification on what Nekota was going for.

 

[DaveinOlyWA]

Cooling for the charging system is most definitely needed.
On my Zenn NEV ot charged at 120 volts and 12 amps and only has cooling fins on the charger and the unit got very hot.

Plus I would imagine that hot areas L3 etc all has to be considered as well

 

[planet4ever]

Plus I would imagine that hot areas L3 etc all has to be considered as well

L3?? Quick Charge doesn't go through the on-board charger at all, does it? I thought the only heat dissipation you had to worry about in the car for that case was the battery itself, and the LEAF battery has no active cooling. Surely the BMS will slow the charging as needed to prevent overheating, so there is no heat issue, only the possibility of a length of charge surprise.

Ray

 

[Volusiano]

Two other related components are the Radiator, and the coolant pump(s) that run when the LEAF wants to circulate cooling fluid, which is low (no) pressure, unlike the fluid in ICE cars.

What is the significance of the low pressure cooling system on the Leaf as opposed to the high cooling pressure in ICE cars?

Is the high pressure in ICE cars simply because of the very hot ICE causing coolant to be hot enough to create the pressure? And possibly the pump must move more fluid faster hence the higher pressure?

Is the low pressure in the Leaf coolant system simply because the cooling demand is not as much as in an ICE car?

 

[planet4ever]

Is the high pressure in ICE cars simply because of the very hot ICE causing coolant to be hot enough to create the pressure?

My only expertise is 55 years of driving cars with radiators, but that sounds right to me, in the sense that the coolant in an ICE can easily get so hot it will boil if not under pressure. Fluid pumps are not very effective at pumping steam.

Ray