Slowing Down In B

[iles]

Enjoyed the imformative review from Seamaster 73, many thank`s for the information. In the review it is shown that braking helps to recharge the high voltage Battery pack. When decending a hill I often selct B which appears to give me more regenerative braking when the brake is used, than it does if B is not selected. Has anyone else noticed this on their Prius, (gen3) or am I imagening things that are not really happening. Thank`s in advance for any replies to my question. Chris.

[Jan&tone]

Enjoyed the imformative review from Seamaster 73, many thank`s for the information. In the review it is shown that braking helps to recharge the high voltage battery pack. When decending a hill I often selct B which appears to give me more regenerative braking when the brake is used, than it does if B is not selected. Has anyone else noticed this on their Prius, (gen3) or am I imagening things that are not really happening. Thank`s in advance for any replies to my question. Chris.

in my Gen2 I would have agreed with you, but the Gen3 seems to charge more when the brake is applied than with B engaged... mind you, when I use B it's a steep hill with a couple of sharp turns so I tend to look at the road rather than the dash!!

unless of course you mean both with B engaged and braking - in which case I've never really noticed...

[iles]

Enjoyed the imformative review from Seamaster 73, many thank`s for the information. In the review it is shown that braking helps to recharge the high voltage battery pack. When decending a hill I often selct B which appears to give me more regenerative braking when the brake is used, than it does if B is not selected. Has anyone else noticed this on their Prius, (gen3) or am I imagening things that are not really happening. Thank`s in advance for any replies to my question. Chris.

in my Gen2 I would have agreed with you, but the Gen3 seems to charge more when the brake is applied than with B engaged... mind you, when I use B it's a steep hill with a couple of sharp turns so I tend to look at the road rather than the dash!!

unless of course you mean both with B engaged and braking - in which case I've never really noticed...

[Grumpy Cabbie]

B is for engine braking such as going down a steep hill. The charge indicator goes a little more to the left purely because the engine is revving more, but because you don't sit with your foot on the brakes as you would have in D, you will actually charge the Battery LESS. There is a hill near me where if I go down in D it will fully charge the HV Battery to the point that the car will actually rev the engine to waste the excess charge. If I keep it in B the Battery will still be one or two bars from full when I reach the bottom.

This is a good thing as you don't want to over cook the HV battery on a long hill too often if you can help it.

[iles]

B is for engine braking such as going down a steep hill. The charge indicator goes a little more to the left purely because the engine is revving more, but because you don't sit with your foot on the brakes as you would have in D, you will actually charge the battery LESS. There is a hill near me where if I go down in D it will fully charge the HV battery to the point that the car will actually rev the engine to waste the excess charge. If I keep it in B the battery will still be one or two bars from full when I reach the bottom.

This is a good thing as you don't want to over cook the HV battery on a long hill too often if you can help it.

[iles]

Thank`s for the explanation Grumpy Cabbie,I will make sure I do not overcook the Battery by using B less than I have done in the past. Chris.

[britprius]

The HV Battery cannot be over cooked by using B or any other mode. With 8 green bars in GEN2 and full charge in GEN3 the Battery is only 80% charged and the HV ECU will stop it charging further. In very hilly terrain it is better to use B to stop over heating the Battery through continous charge (down hill) and discharge (up hill) cycles, but even this is limited by temperature censers in the battery making the ECU limit battery current.

[Grumpy Cabbie]

Well it doesn't over cook it as such but let's just say it isn't happy. When leaving in Drive I've had all bars lit on my Battery and the engine will rev to disperse the extra charge going into the Battery. Then when I reach the bottom of the hill the car will run on electric only right upto about 50 mph allowing acceleration right upto the red power band (like in EV mode but it goes upto 48 mph) as it tries to use up the excess charge and get back into the happy zone at about 80%. Once the charge is down to one bar from full the car starts to behave as normal.

Also coming down this hill the car has been known to switch off regen braking completely when the Battery is completely full (full to its set limit, though not full full) and this can be rather alarming as the loss of regen can affect the braking force. On the subject of cooking batteries, I have also had the battery fan blow hard if I go down this hill in D (it sounds like a loud hair dryer), so technically I am not cooking the battery as such, but the car isn't happy with the high rate of charge pumped into it.

Using B mode down the hill avoids all the above nastyness and the battery guage is 2 bars from full. Lots of heat and or high charging will reduce the life of the HV battery. There are reports on the US forum of owners in mountain areas having battery issues at around 150k miles - granted probably more than most UK users will ever get to, but it is lower than the normally reported life of 200k-250k.

Hope this gives a little more insight into how using B going downhill helps things.

[iles]

Well it doesn't over cook it as such but let's just say it isn't happy. When leaving in Drive I've had all bars lit on my battery and the engine will rev to disperse the extra charge going into the battery. Then when I reach the bottom of the hill the car will run on electric only right upto about 50 mph allowing acceleration right upto the red power band (like in EV mode but it goes upto 48 mph) as it tries to use up the excess charge and get back into the happy zone at about 80%. Once the charge is down to one bar from full the car starts to behave as normal.

Also coming down this hill the car has been known to switch off regen braking completely when the battery is completely full (full to its set limit, though not full full) and this can be rather alarming as the loss of regen can affect the braking force. On the subject of cooking batteries, I have also had the battery fan blow hard if I go down this hill in D (it sounds like a loud hair dryer), so technically I am not cooking the battery as such, but the car isn't happy with the high rate of charge pumped into it.

Using B mode down the hill avoids all the above nastyness and the battery guage is 2 bars from full. Lots of heat and or high charging will reduce the life of the HV battery. There are reports on the US forum of owners in mountain areas having battery issues at around 150k miles - granted probably more than most UK users will ever get to, but it is lower than the normally reported life of 200k-250k.

Hope this gives a little more insight into how using B going downhill helps things.

[iles]

Thank`s Grumpy Cabbie for the exelent reply regarding Battery cooking, I now understand what is happening when braking in B or braking in D. Only on one occasion has the hybrid Battery reached a fully charged condition after a long decent, and as you experienced the car drove on electrical power for some time afterwards. Thanks once again for the clear easy to understand explanation. Chris.

[Grumpy Cabbie]

What I forgot to add is that the car will look after itself. Even if the HV fan is blowing or you go down a steep hill and the car revs its head off afterwards, it is still normal - the car is programmed not to overload so as to damage itself.

In other words only worry if you get warning lights come on.

[johalareewi]

Also coming down this hill the car has been known to switch off regen braking completely when the battery is completely full (full to its set limit, though not full full) and this can be rather alarming as the loss of regen can affect the braking force.

Once you lose regen braking because the Battery is full, you only have friction brakes which on a long descent can also overheat (not good). Always worth slipping into B when passing low gear now signs! Remember to switch back to D at the bottom of the hill.

[capnbirdseye]

.

Once you lose regen braking because the Battery is full, you only have friction brakes which on a long descent can also overheat (not good). Always worth slipping into B when passing low gear now signs! Remember to switch back to D at the bottom of the hill.

I've only tried it once so far and that was coming down the big hill at Broadway Glouc's where it worked very well ,'B' definitely adds charge as it was green when I got to the bottom, the only thing that confused me was did I need to touch the brake pedal to go back to D and confuse the bloke behind me or would it have worked without?

[Jan&tone]

.

Once you lose regen braking because the battery is full, you only have friction brakes which on a long descent can also overheat (not good). Always worth slipping into B when passing low gear now signs! Remember to switch back to D at the bottom of the hill.

I've only tried it once so far and that was coming down the big hill at Broadway Glouc's where it worked very well ,'B' definitely adds charge as it was green when I got to the bottom, the only thing that confused me was did I need to touch the brake pedal to go back to D and confuse the bloke behind me or would it have worked without?

it doesn't need you to touch the brakes to go from b to d.... only when you go from n or p to d or r....

[iles]

What I forgot to add is that the car will look after itself. Even if the HV fan is blowing or you go down a steep hill and the car revs its head off afterwards, it is still normal - the car is programmed not to overload so as to damage itself.

In other words only worry if you get warning lights come on.

[iles]

Thank`s Grumpy Cabbie for the update, I am on my sixth Toyota car and all have been very reliable. No warrany work was required on any of the other five, and I hope the Prius will be the same. Thank`s again, Chris.