[Frequent Flyer Frank]

After reading the recent thread on the battery running down in traffic, I remembered a previous event that I wanted to ask about.

On a recent trip from Anaheim CA (Sea Level) to Las Vegas NV and back (over the San Gaberial Mountains), I noticed coming down Cajon Pass that the battery charge indicator in the MFD got all the way up to eight solid green bars. The vertical drop is from 4300 ft to about 1200 ft in about 9 'ish miles so this condition existed for about 4 miles (about 7 minutes).

Since I have a 6.6 Kw solar electric power system with battery back-up, I know how important it is to have a charge controller that can take extra energy and divert it (if necessary) to a "dump" load.

I hope that the brillant engineers at Toyota have thought of this. Anyone know for sure?

Great forum. :lol:

 

[jeromep]

First off, 8 green bars is about 80% of total capacity. The system computer will do its bets to not allow the battery to get beyond this top level of charge. As an aside, if there are no bars the battery is down to about 40% total capacity, of which the vehicle will start to run the ICE to turn one of the MGs to recharge the battery.

The way it "burns off" charge beyond that upper point is to spin the ICE without lighting up ignigion, and of course to use the MGs to power the vehicle instead of or in conjunction with the ICE. People describe the spinning of the ICE without ignition like the vehicle is engine braking or dieseling. You can feel the ICE spin alternately, however it never "catches".

I supose the dump load would be spinning the ICE to release surplus energy that the system doesn't want onboard.

 

[DanMan32]

Another approach Toyota could have used was to not use MG2 at all once the battery was topped off. In other words, go into neutral. Of course in that case, you have to use friction brakes, like in any other car.

 

[Astrowoman]

I had the ICE come on to "burn off" extra charge on my first road trip, going over the grape vine. It does seem as if there ought to be a better way to dump the energy... I guess technically in a conventional car that's what the brakes are doing. Why DOESN'T the Prius have a switch to go into friction-brake-only mode when the battery is at that level? Or some sort of ballast "device" to run off the battery... flashing neon sign or automatic carpet vacuum or ..... ????????

 

[richard schumacher]

Pumping and heating air with an un-fuelled ICE is a perfectly fine way to burn off excess power. This is what "Jake brakes" are on large trucks. Locomotives use large banks of air-cooled resistors as a load; I don't know why they don't use the "Jake brakes" method.

 

[hyperion]

The ECM should protect the Batteries from ever being "over charged" If it doesn't Toyota will replace the whole smuck. It sounds a a lot like the guys that turned their headlights on when they thought they were looking at over charging on their ammeters. No problem here cause "no ammeters." My thoughts would be to turn off the MFD and let Toyota engineering take care of it. It could not be anything they didn't think of. The Prius has been around for a few years and I'm sure has been driven over these types of roads many times and so far I have read of no problems other than the catastrophic failure of the power transfer units. (not protected by warranty?)

 

[Paulie]

Pumping and heating air with an un-fuelled ICE is a perfectly fine way to burn off excess power. This is what "Jake brakes" are on large trucks. Locomotives use large banks of air-cooled resistors as a load; I don't know why they don't use the "Jake brakes" method.

Probably noise! Loud as all get out those things! I see signs on the highway saying no engine braking, so I stay out of B mode. LOL

The new commuter locomotives that Metra (chicagoland) uses actually go to a slower speed idle at stop to have less noise and save fuel. Pretty cool. Shows GM's Electromotive division should be building CARS AS WELL!!! HELLO GM!!!

 

[DanMan32]

Pumping and heating air with an un-fuelled ICE is a perfectly fine way to burn off excess power. This is what "Jake brakes" are on large trucks. Locomotives use large banks of air-cooled resistors as a load; I don't know why they don't use the "Jake brakes" method.

Probably because the diesel engine isn't connected to the wheels.

 

[richard schumacher]

Pumping and heating air with an un-fuelled ICE is a perfectly fine way to burn off excess power. This is what "Jake brakes" are on large trucks. Locomotives use large banks of air-cooled resistors as a load; I don't know why they don't use the "Jake brakes" method.

Probably because the diesel engine isn't connected to the wheels.

D'ohh!! of course. The alternator on an existing loco can't turn the ICE. If it did, then "jake brakes" would be feasible. It must have been simpler just to provide resistor banks, given that there was no other reason for the alternator to act as a motor.

 

[jeromep]

Probably noise! Loud as all get out those things! I see signs on the highway saying no engine braking, so I stay out of B mode. LOL

The new commuter locomotives that Metra (chicagoland) uses actually go to a slower speed idle at stop to have less noise and save fuel. Pretty cool. Shows GM's Electromotive division should be building CARS AS WELL!!! HELLO GM!!!

I've had instance to use B mode on a long downhill stretch on the highway once. It isn't loud like a Jacobs brake, however it is not quite either. At highway, downhill, "freefall" speeds you can definitely tell that you are compressing air. This brings up a rather academic question, doesn't running compressed air through the CAT for an extended period of time actually cool it down?

 

[stevewa]

Pumping and heating air with an un-fuelled ICE is a perfectly fine way to burn off excess power. This is what "Jake brakes" are on large trucks. Locomotives use large banks of air-cooled resistors as a load; I don't know why they don't use the "Jake brakes" method.

Probably because the diesel engine isn't connected to the wheels.

D'ohh!! of course. The alternator on an existing loco can't turn the ICE. If it did, then "jake brakes" would be feasible. It must have been simpler just to provide resistor banks, given that there was no other reason for the alternator to act as a motor.

It was a re-work of existing technology. Electric locomotives (with an overhead wire or third rail power supply) had regenerative braking, just like our hybrids, except they fed the power back into the line for the loco climbing the hill to use. Since diesel-electric eliminated that possibility (but they still wanted to have the ability to brake using the motors) they had to find somewhere to put the energy. Bingo, toaster wires on the roof and big fans to cool them.

 

[jsp]

First off, 8 green bars is about 80% of total capacity. The system computer will do its bets to not allow the battery to get beyond this top level of charge. As an aside, if there are no bars the battery is down to about 40% total capacity, of which the vehicle will start to run the ICE to turn one of the MGs to recharge the battery.

The way it "burns off" charge beyond that upper point is to spin the ICE without lighting up ignigion, and of course to use the MGs to power the vehicle instead of or in conjunction with the ICE. People describe the spinning of the ICE without ignition like the vehicle is engine braking or dieseling. You can feel the ICE spin alternately, however it never "catches".

I supose the dump load would be spinning the ICE to release surplus energy that the system doesn't want onboard.

... THANK YOU! I was very glad to find this info today -- because that explains what happened with us over the weekend... ! Driving back roads in the mountains of southern CA (oddly enough, to avoid a bad traffic back up, LOL!) - and had the display on "map"... suddenly there was this wierd sound like an engine surging, only it didn't *feel* like it was -- switch display over to engine status and the thing was totally maxed out on green... spinning ICE would explain it! My theory - since it literally felt OK - was that it might have something to do with handling an overcharge -- Went on to drive just fine - and it only happened once, but it was certainly disconcerting. ALSO - it's only been since that "reprogram" due to the engine die at redlight a month or so ago that it seems like it spends SO much more time in the green than it used to... anybody else notice that?

Again - many thanks for this forum!!