Heater 'growling' when engine is stopped

What gear are you in when you stopped at the drive through. In drive if you do not have your foot on the brake the car will be trying to move forwards using some battery. In neutral the car cannot charge the battery. In park it will charge the battery, but this does not always show on the display and is slow because of the lack of engine speed.

John (Britprius)

 

Hi John, thanks for the reply.
I never use neutral (except when I'm entering drive-thru car wash)
I do notice that the arrow from engine to battery often appears when I have my foot on the brake (in 'drive'), and when it does I usually double tap or tap harder till it goes away. I suppose the battery is still charging?

But, to answer your question, I am always in 'park' at the drive-thru. If the battery is being charged, then it must be charging at an extremely slow rate, because I sure can't tell!
I've definitely seen it go up 1 bar far faster (when starting cold, probably because it's revving higher).
But, I mean each bar on the graph represents about 81 watt-hours, and I've calculated that the Prius uses .01 gallons/ minute when idling.....that's 337 watt-hours of gasoline per minute.
So, unless I'm missing something, it should at least go up 1 bar for every minute (or two) of idling, no?

 

Hi Scorpion. If you have arrows from the engine to the battery in D when stationary that shows the battery is charging (normal), but if the arrows are from the battery to the wheels. Either your foot is not pressing on the pedal hard enough or the brake switch is out of adjustment or faulty.
The bar graph on the MFD is not linear. The two top blue bars represent a much larger proportion of the battery capacity than the rest.
The Prius engine is only 40% efficient at it's best, you then have to remove any mechanical losses in the transmission, mechanical to electrical conversion losses in the generator, inverter losses, and battery charging losses before showing how much petrol energy ends up in the battery.

John (Britprius)

 

These are the sorts of realities that we engineers live with, that cause us to be such a cheery lot. And they call economics "the dismal science"!

 

Haha....well, I am an economist!
Which is perhaps why I can't understand how burning 337 watt-hours of gasoline (per minute) is unable to produce at least 60 watt-hours (per minute) of battery charge (less than 20% efficiency).
If the ICE would act as a generator (while idling for heat) and put just 60 watt-hours into my battery (per minute), I'd have a fully charged pack in way less than 10 minutes (since usable capacity is only 650 watt-hours).

 

The low charge rate could have something to do with the battery temperature. If they are quite cold, I think the battery ECU might limit the amount of charging current, but that is a guess. The same thing does happen when the batteries are hot, and the ECU will limit the current until they cool off a bit.

Also, if the car is just coming on from a very cold start, and cabin heat is called for, that will initially be supplied by electric heater resistors, rather than from engine heat. That keeps the ICE running without doing much charging.

 

I think you are on to something, but I really wish I knew what the charging rate actually was. The MFD doesn't give #'s; in fact even "if" the battery is charging, there is no arrow going from engine to battery. And then there's the issue of regen.....

Yes, that's probably true....although the thermal management system should keep it at optimal temps (unless it didn't have time if you started the car @ 115 degrees)
As far as the whole idea of limiting charging current when battery is too hot or too cold, that makes sense to preserve the battery, but it seems you would also want to limit regen since that is uncontrolled high current, whereas engine generator should be able to regulate charge rate to an appropriate current for a given temperature

I am glad you mentioned this. I was just about to ask this question which really throws 'cold water' on the whole "acting as generator while idling for heat"
Today in Nebraska, it was minus 5 degrees when I left my apartment, minus 30 with windchill (it says you're located in Hawaii, so you may have hard time relating )
Anyhow, I wanted to 'warm up' the car, so I turned it on and the engine sprang to life immediately rather than waiting the normal 5-10 seconds (I've found it does this in extreme cold temps).
I noticed the battery gauge was green with 7/8 bars. I then turned the heater to 'Hi' and 85 degrees and went back inside my apartment to collect some items. I came back down 5 minutes later and noticed the battery gauge was now blue with 6/8 bars!!
That's right.....after 5 minutes of idling, with the car never having been shifted to R or D or even moved 1 inch, I lost battery power!
So, the only reason I can think of as to why this happened was the power used by the resistance heater?

 

I would get yourself hooked up with one of the Prius monitors available. Torque, Scangauge, or Prii-Dash. You get to see all the currents you want.

The heater resistors are called "PTC HTR" and are fused @ 30A each. So hundreds of watts used there. Until the ICE is all the way hot, they get cycled and make for some battery drain. Also, at warm up time the car will use the ICE as little as possible, in keeping with the ultralow emissions category. So charging will be limited again.

I do notice that, on a long downhill, with the battery taking in much regen current, the car will suddenly switch to friction braking only, or sometimes it will allow only small amounts of regen. One can hear the change in inverter noise when this happens, and see it in Prii-dash. This occurs when the batteries are at the upper end of their optimum temperature range. So there is control of regen that keeps the batts from overheating via braking.

I was from MN long ago, so I can indeed relate.

 

If you really want to know, it is fairly easy to find out. If you have an Android phone, the Torque app is a great tool. You need a OBDII bluetooth adapter (cheap on eBay and Amazon) and the Torque app itself ($5 on the Google Play store).

Once you get it all set up, you can read the current in or out of the battery in real time (and lots of other stuff).

Attached are some screen shots showing how I've got mine set up.

 

I've noticed that in cold weather, when I turn up the heating to anything between 20c to 22c, when I stop in traffic with the heater running, my engine continues to run for a while, spinning away but using no fuel and of course not charging the HV battery.

It sometimes even does this when I'm gliding and / or going downhill. This usually happens when the HV battery has several blue bars or even green bars.

My understanding is that the HV / MG2 (or MG1? Someone please verify) are keeping the engine spinning over without using fuel, purely to create heat for the heater matrix.

At that particular moment, the computers aboard the Prius are trying to conserve energy, and have decided (unanimously?) that it is better to keep the engine spinning on with electrical power than to switch to using fuel.

Perhaps I'm wrong, but it seems logical.
What an amazing piece of advanced technology the Prius Gen II is - almost like a road going Space Shuttle festooned with so many sophisticated decision making computers.


iPad ? HD

 

The engine is kept spinning by MG1 to lower the charge on the HV battery, although sometimes it will be running to provide heat.
In cold weather the battery gets charged to a higher level than in warm weather because the engine runs for longer periods just to supply heat for the cabin. In doing this it also charges the HV battery, and the Prius system tries to keep the charge level at around 5 blue bars. Doing this helps ensure battery longevity.
There is a separate electric coolant pump that runs when the engine is not running to circulate hot coolant from the engine into the heater core.

John (Britprius)

 

I'm not so sure that the engine can run with absolutely no fuel used? If someone could weigh in.......
I thought so too at one point, since I didn't see any bars going from engine to pack to indicated charge...... or, when I was driving, it clearly indicated drive power was coming exclusively from pack, but I was getting less than 99.9 mpg.

I decided to run a little experiment using the consumption screen as opposed to the efficiency readout.

On a very cold day, I made sure the heater was off, and waited till the engine cycled off normally. Then, I turned the heater on to 'Hi' -which of course turned the engine back on- and let it run 5 minutes (It was minus 10 outside!)

Starting mpg: 13 miles @ 33 mpg, or .39394 gal.
Ending mpg: 13 miles @ 29.6 mpg, or .43919 gal

So, a total of .04525 gallons used over 5 minutes (exactly; used stopwatch)

I realize the gallons part is ballpark, but I've done the experiment several times and concluded that the engine used between .01-.02 gallons per minute (depends on temp) when idling, even if it appears to just be spinning and not charging the pack

 

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Scorpion, the engine is sometimes spun by MG1 without fuel. This acts as a load on the MG to lower the state of charge of the battery. This confuses people into thinking the engine is running when it is not.

John (Britprius)

 

I was referring to the engine spinning on sometimes (and for a while) without any fuel being used - when at a standstill or when gliding @
- this definitely happens, and I seemed to notice it more often when I've turned the heating up. It happens a lot less at 18c. The reason has just been explained by Britprius.

Nexus 7 ?

 

It is also true that the MFD will show only electric propulsion, or no propulsion, but register less than 99.9 mpg. This is the engine running simply to heat itself to optimum temp, while not providing power to the wheels. In my case, I go down a long hill when I first leave, and there is only braking going on, but the engine is running to heat up. It also happens on longer downhill coasting, when the previously warm engine has cooled down too far and again is run to get back up to temp.

 

This will only happen if the HV battery is completely full (maxed out green bars). It will surge on and off.

There is no way the ICE is generating heat unless it is consuming gas. There are electric supplemental heaters, but they only consume electricity and do not require the ICE to spin.

 

I believe North America is the only place where the electrical (PTC) heaters are fitted possibly part of the emissions control requirements for the CARB states. They are not fitted in the UK/EU Prius and can see no logical reason for them to be fitted in the Australian version. Along with those omissions are the thermos tank, pump, control valve, and tank bladder.

John (Britprius)

 

This is very interesting, I did not know that the electric heaters are not fitted in your geographic area.

I'm not sure that the motivation for including the electric heaters is emissions-related. The docs that I've seen point towards providing supplemental heating since the engine doesn't produce much excess heat.

Is it possible that Toyota thinks that the winter climate in UK/Europe is not as cold as in North America?

 

The same applies to Norway, Sweden, and the rest of Scandinavia where the climate is just as cold as North America.
My thinking was the PTC heaters are there to allow the engine to warm up quicker without having to supply warm coolant to the heater, perhaps not having the electric coolant pump turned on while warm up was in progress. This is only supposition on my part, but it is a fact that this side of the pond we do not get the PTC heaters, or heated mirrors. A big mistake by Toyota.

John (Britprius)