Regen Braking Not Working Sometimes

[rhwinger]

This morning (and on one other occasion) I noticed that the regenerative braking wasn't working for a short period of time. I could feel the brakes behaving differently - I had to push harder on the brake pedal - in order to slow down/stop. The green regen bars would not come on during brake pedal movement, but when I took my foot off the gas, the green bars came on. My battery SoCharge was less than full.

Anybody else experience this?

Could I expect the diagnostics to be able to detect this and register an error code that can be read later?

Thanks in advance.

Bob

[Chuck]

The only reason apart from a malfunction I can think of is you were going less than 15mph. To discourage extreme downshifting, the regenerative braking cuts out at about 13mph for the Insight.

[brick]

Could be a cold weather thing. The Prius protects the pack like mad in this weather, even when it's closer to 0C than 0F. Current draw from the pack is limited to practically nothing until it warms up and I suspect that the same is true of charging, though the effects are less apparent. We're both working with the same battery chemistry so I suspect Honda would implement similar protections. Just a guess.

[rhwinger]

Thanks Bob and Tim.

I called the Honda service dept and they said they would have to actually see the failure in order to diagnose.

Temps were in the mid 30's when this happened. As for speed, at one point I was in a 15 mph zone, but the condition persisted even when I was driving (braking) in a 35 mph zone. And heading home this afternoon, no braking regen even when I got out on the larger secondaries. But then I noticed a 3-4 bar forced charge about 2 miles after starting the drive home. After the forced charge terminated, I noticed the regen braking started working again. Go figure?

I'll note the behavior on the service ticket for documentation purposes when I go in Friday for a tire rotation.

Thanks all.

Bob

[tarabell]

I'm curious, did you have either the heater or the front windshield defrost on at the time?

[HCHCIN]

Bob--

I notice this often in my new HCHII here in much-colder Ohio. For probably the first five minutes of my commute (sometimes longer if it's colder) I won't see regen on braking, but I will commonly see one or two bars of forced charge under power for part of that same five minutes. My unproven theory is that the battery management system does this to warm and protect the pack, but I don't know the technical reason this might be.

The behavior you note is consistent and predictable with me. In warmer weather I see behavior more like you've come to expect. Perhaps it's only just now gotten cold enough in Virginia for you to experience this phenomenon? --RN

[rhwinger]

Originally Posted by tarabell

I'm curious, did you have either the heater or the front windshield defrost on at the time?

Hi Tarabell, I have been leaving the heat temperature control set to 70 degrees or something like that. I almost never turn on the fan, and leave the air vent control to allow outside air to come in. This "ram air" provides a whisp of heat and the fresh air almost always prevents windshield fogging. I'll turn on the fan if passengers request it, but this method keeps me comfortable even down to 10 degrees.

Can't remember when I last turned on the defogger. Keeping the car in the garage helps a whole lot.

Thanks,

Bob

[rhwinger]

Originally Posted by HCHCIN

Bob--

I notice this often in my new HCHII here in much-colder Ohio. For probably the first five minutes of my commute (sometimes longer if it's colder) I won't see regen on braking, but I will commonly see one or two bars of forced charge under power for part of that same five minutes. My unproven theory is that the battery management system does this to warm and protect the pack, but I don't know the technical reason this might be.

The behavior you note is consistent and predictable with me. In warmer weather I see behavior more like you've come to expect. Perhaps it's only just now gotten cold enough in Virginia for you to experience this phenomenon? --RN

Thanks, your observations make me feel a little better. And your unproven theory about protecting the battery makes a lot of sense. The drive in yesterday morning was in the low 20 degree range, and the braking thing happened when I drove the car before lunch with ambient temps in the low to mid 30's. Maybe the pack was still cold from the cold soaking out in the parking lot? Is there a way to monitor the pack temp? ScanGage?

Appreciate all your comments and suggestions very much.

Bob

[tarabell]

For probably the first five minutes of my commute (sometimes longer if it's colder) I won't see regen on braking, but I will commonly see one or two bars of forced charge under power for part of that same five minutes.

I've also noticed for the first 5 min there's no regen when I take my foot off the gas--only sometimes see the bar or 2 of forced charge at that time.

[Mike Dabrowski 2000]

The Insight system is different, but both follow many of the same control rules.
A look at the regen current into the battery when the battery pack is less than 30F will show a saw tooth wave rather than the normal steady DC. The system will only allow about 20A of regen, and will only allow about 35A of assist. Once the battery gets over 42F, everything settles into normal operation.
This is because the NIMH batteries can not accept charge or produce current as well when cold. Keeping current in and out gentle while the pack warms up helps maintain the SOC balance on the individual cells. I am sure that many other factors are being considered.

The Ford Escape has 250 NIMH D cells in it's pack. Has a separate AC system to keep them cool, and a heater to warm them up if too cold. Thats the type of battery control system that we need on all systems.
I have an indoor outdoor temp display in the car, with the outdoor probe right in the battery pack. The normal operation returns almost exactly at 42F.
This does not mean that your car is ok, just something to watch if the symptoms return.