HV Battery Blower Maintenance

Excellent post.

With you living in Florida I can just about assure you that your battery blower motor runs. The motor is very quiet and hard to hear at low speeds. If you have a SGII or other OBDII device you can monitor this along with the battery fan speed.

I have thought about connecting an external power supply to my battery fan also. The existing fan controls work well as long as the car is in Ready mode. Once you stop the car, especially after city start/stop driving, the battery temps are elevated and they will continue to climb when the car is turned off and the fan stops. I have seen the battery temps increase 5-10F after the car sits for an hour or so.

One guy on here came up with a printed circuit board with an adjustable timer so he could run his fan for 15 to 30 minutes after the car is stopped. Another guy hooked his up to an external power supply and runs his fan at high speed all of the time while the car is on.

My guess is that Toyota had a trade-off between running the battery fan after the car was off and the additional drain on the 12V battery and chose to not run the battery fan.

 

I wonder if it would be possible to connect a small low power solar panel (through a diode) so that it operated in parallel with the existing controller. I was thinking of something with just enough juice to keep it ticking over when it's parked in the sun.

 

If you have a scangauge 2 you can set it up to run the fan at any speed you want.

 

Yes, I have tested the scangauge control of the battery fan speeds. It works fine. Running the fan constantly at a low speed should help with the battery temps. I just think the battery ECU control of the battery fan works OK.

The only problem that I see is that the fan needs to run for some period of time after the car stops to keep the temps from continuing to rise.

 

Of course you're free to modify and adapt your vehicle in any manner you wish.

But it seems to me, you have 65,000 miles on a 6 model year old vehicle. Your own inspection revealed little dirt build up in the fan. You say you've rarely heard it turn on. You haven't had a problem so far.

I wouldn't make the assumption that any changes to the operating system in regards to the HV battery blower need to be made. Kind of seems like the typically American attitude that "more" is always better.

Of course I don't live in Florida...The Pacific Northwest is much more forgiving in terms of surrounding cooler temperatures.

 

If you have to run the blower fan after the Prius is powered off, you can get a Hella time delay relay that can delay from 1 to 900 seconds.

Without drawing it out I think if you hooked up a NC relay to 12V switched feeding the time delay relay it should work fine.

When you power off the car the NC relay would close and would supply 12 volts to the time delay relay running the blower for whatever length of time you set.

When you power the car on, the NC relay would open and the system would return to normal.

 

Do you have any info on the Hella time delay relay?

One thing that I would add to your description above would be to add a NO relay contact to the blower feed from the ECU so as not to backfeed the ECU while supplying external 12V to the blower.

 

Hella 996152131. They cost about $30.

I used one in my jeep to turn my headlights off after I parked it. Worked better than jump starting it all the time

 

One note for anyone thinking about running the HV battery fan blower motor with an external power supply, I took the following readings while testing the SGII XGauges:

BFM = 1, CF0 = 34% and VMF = 1.3V​

BFM = 2, CF0 = 41% and VMF = 2.0V​

BFM = 3, CF0 = 48% and VMF = 2.5V​

BFM = 4, CF0 = 55% and VMF = 3.0V​

BFM = 5, CF0 = 63% and VMF = 3.5V​

BFM = 6, CF0 = 72% and VMF = 4.0V​

​

As you can see at the highest battery fan speed at BFM (battery fan mode) = 6, the voltage to the blower fan is only 4.0V. I am not sure what connecting 12V directly to the blower fan motor would do. I am sure it would be extremely loud since at BFM=6 the fan was pretty loud.​

Of course this assumes that the SGII XGauge feedback is correct.

 

I wonder if those voltages could be right. Prii-dash shows my fan voltage to hang around 6-9 volts, and the sound is not audible unless I put my head close to the vent.

 

Interesting. Assuming that is correct, you can get a DC step down module on DX for about $10. Just add it to the output of the time delay relay.

Then you could dial in whatever speed you would like after shut down.

 

I see you have a 2009. I have the 2010. I wonder if this has to do with the difference in the two fan controls. I know there were some basic differences between the Gen II and Gen III battery systems.

I cannot hear my fan normally since the highest I have seen it is BFM=4. When I tested it with the SGII and got up to BFM=6 I could hear the fan close to the vent, as you said.

Without testing with a voltmeter I have no idea whether these voltages are right or not. All of the other SGII data for the battery fan seems to be correct. I know I have seen others report similar data for the battery fan speeds based on HV battery temps.

 

I just checked the Repair Manual for my car and it lists the battery fan voltage range as 0-5V. It also lists a test for Battery Fan Mode 1 = 1.0-1.4V. The SGII value for Mode 1 = 1.3V. So it appears these are correct voltages.

 

OK JD, interesting. That does look like a difference in the two models. A curiously low voltage for a fan motor. I usually associate low voltage motors with reduced efficiency, so they must have had some compelling reason to change.

 

Yes, I was surprised with the lower voltage. I was expecting a range from 0-12V.