2003 HV battery question

I have an electrical engineering background and have been following the Prius stuff. I was driving a friends 2003 NHW11 with only 55k miles, but it seems to me the NiMH battery might be showing signs of aging. Unfortunately I don't have access to a scan tool check all the good MG1/2 temps and the pack conditions.

My concern is the SOC bars appear to always be at 60% which isn't necessarily a bad thing, but I cannot get the HV battery to run down to a lower bars and even when trying my best to drive around in EV only trying best to avoid ICE kicking in under 30mph. And even just driving at 20mph and only keeping up with rolling resistance not accelerating or hills, at some point the ICE kicks in. I'm unable to see the SOC go down at all (or up). Even on trip and hour at 65mph, with hills and regenerating all the way down, it appears to not even rise much. At most you might get one of those 50Wh blips, but even those are rare and require an exit ramp of a freeway, when driving around town in stop and go even trying to do your best to coast/regen etc. those 50Wh blips are very rare.

Basically the ICE seems too often to be charging the HV battery. The SOC doesn't vary at all (which may not be a bad thing, but even driving hard the SOC doesn't seem to decline).

I guess I am leaving out the important part that over the lifetime this 2003 averages about 37 mpg. Which may not necessarily be odd but seems like an outlier from all the mpg charts I have seen.

Short of a scan tool, would this be a concern? I know I need to throw some ammeters around MG2 and the HV pack. Is there a way other than idling with fuel pump relay removed to exercise the HV battery? I guess it is isn't a problem, it just is nearly always running ICE even with the lightest pedal, even in conditions I'm not sure it should. Is it possible the computer tries to run on EV only and the battery pack voltage starts to drop too quickly, like an aging NiMH cell would, so it kicks in ICE more often to compensate?

I have checked the generic ODB2 stuff and at least the engine side coolant is still at 192 F after a long drive then sitting for 10 mins.

Thanks for any other experience.

 

Ok, an update, after posting I decided to investigate more.

It appears to have the heavy hand pedal issue because I cannot reasonably accelerate without the ICE kicking in at all at any speed. However, if the ICE cuts out (coasting or tap brake) I can accelerate very very slowly, if I depress the pedal about 1mm and only accelerate at 1 mph per second. So 10mph... wait.. 11mph... wait.. I can get it to stay on MG2 only. Any quicker than that and the ICE kicks in. If this isn't a description of the pedal problem, then it must be something to do with the HV battery current and the ECU decides it needs more from the ICE to protect batteries.

So, I was able to drive around for about 15 mins going 15 to 25 mph with headlights on and forcing EV only by judicious use of coasting, and tapping the brake to cancel the ICE everytime it came on. I drove around like this with mostly MG2 (ICE less than 10% of the time). The battery display did finally jump from 6 bars to 3 bars. After another 15 mins of driving normally and letting it sit a few minutes, the next time I turned it on it was back at 6 bars. (top one for blue). I attribute the jump up to SOC update rate seems laggy and maybe the batteries cooled down some.

I have never seen this SOC go above 6 bars, including 65 mph down some pretty good freeway inclines where I was coasting from 65 down to 50 mph. Never went above 6 bars with a two hour drive with cruise control on flat terrain and display indicating ICE was charging the HV most of the time on the display at least. I imagine if I was in stop and go for 30 mins I could get it down to 2 bars.

Anyways, just wondering if this is normal or indicates battery aging. It only has 55k miles, but I know I have dealt with many power tool NiMH packs that behave with this flattened out voltage discharge curve that were not at a 5000 cycle end of life, but just older chemistry.

[EDIT -- If I am going 70 mph and put it in "B" and regenerate braking down an incline (say 30 seconds of regeneration), the SOC should go up a bar? ]

 

Is there a similar chart for Gen 1 HV voltages as this one? forums/gen-ii-prius-care-maintenance-troubleshooting/51939-hv-battery-soc-wrong-after-flat-12v-battery.html#post744223

I have right equipment to measure high voltage DC (except the gloves.. womp womp) I guess I just need a scan tool to figure out what is going on.

 

Thanks. No, I'm well familiar with the disconnect and battery pack and the contactors. I just was meaning measuring the 238V or whatever instead of the cells. I know I should off the shroud and measure cells.

I'm thinking I need to back probe the MMT(MG2) / MMT(MG1) on the H10 connector as I don't have a good scan tool only OBD2 generic. So I think I might see what those temp sense voltages are.

I'm worried the ICE coolant is 200 to 207degF on a hot day. And there is air in the Inverter coolant.

 

I believe it is in S4. I am saying that it is impossible to accelerate at a reasonable rate without the ICE kicking in. So the car is warmed up complete stop at stoplight, the ICE will kick on if you accelerate at a rate faster than like 1 mph increase per second (which is insanely slow increase in speed and takes like 20 seconds to get up to 25 mph). It will stay in golfcart mode if you never depressed the pedal more than say 1cm. Any acceleration at any speed or any condition except what i mentioned will kick in ICE. It has no problem shutting of ICE when you coast or brake.

So it could be a pedal issue with Gen 1, or my thinking is that as it runs in golf cart mode, the EV only is draining the battery at a rate that either the battery internal resistance voltage drops or heating causes it to say, I need more current, I'll turn on the ICE.

I can drive at least 500 ft in reverse at a fast speed and good power.

 

It could be a Gen 1 behavior isn't as refined as Gen 2.

My hunch is that there is more going on like it must monitor battery temp and the battery current. If you have bad cells then when you draw 10A the battery voltage will drop too quickly, or maybe the cells heat up too much because the battery fan is clogged a little, so in those cases it might make sense to kick in the ICE.

Of course I'm concerned about this pedal wiper problem, and/or it is normal behavior.

Basically the battery is just being used as a capacitor in my case. It stores a small amount of regen braking and uses the HV battery a small amount to assist the ICE and also it runs the batterys, but the current is mostly going straight from ICE to battery to MG2 and the battery voltage is being held nearly constant by the ICE kicking in and out.

In city traffic it appears not to use any significant battery voltage range and runs the ICE all the time. So I still wonder about degraded battery might be causing the lack of range.

 

Read this..

Through more aggressive use of brake tapping to force regeneration, and a few 15 min sessions of finding a location to drive around in some 25 mph golf cart mode (or reverse) I believe I have run the battery through a wider voltage range and what I suspect is a slight memory type effect, using more range on the battery has enabled better S4 functioning and less constant ICE usage.

Note, my belief is regarding acceleration that (assuming temps are ok and the A/C is off) the ECU monitors IB the HV battery current and when you accelerate with too much battery current the ICE kicks in. This is the limiting behavior which is what people mention above that it is ok in golf cart mode for maintaining speed, but hard to accelerate in golf cart mode.

I have NOT been able to get into any of the green bars (9,10) which concerns me and the range seems quite stunted but still health battery (jumps from 8 to 6, nothing else). I should find a very very large hill and see if I can get into the green to promote better battery range. This is a low mileage, ten year old battery with constant driving conditions so the HV I don't think has seen much S4 driving.

 

Seriously, try to get more of a voltage range on your HV battery. I suspect years and years of a narrow range may lead to a semi memory effect. At the very least a deep discharge may act to semi-balance the cells. You can force discharge the batteries by driving in reverse, or driving under 35mph tapping the brake and then trying to maintain a speed without the ICE coming back on. Keep tapping the brake when ICE is on.

It may be unhealthy to do this for a long period of time or in hot weather. You do not want to overheat the motors or the HV battery. Maybe keeps this activity to under 15 mins. Make sure the inverter pump is working and no air bubles. So be smart about it, but you should be able to get other bars to show up. So try to get down to 4 bars, then drive around and use lots of coasting/regen braking, especially in "B" under 35 mph and you will charge the batteries back up, or I believe in "P" or something you can rev the engine and force charge the battery because MG1 has to spin.

When you exercise the HV battery a little more, you will see more usage of the golf cart mode.