Traction Battery Preventative Maintenance - Hybrid Automotive Chargers

Being retired and disabled I find it difficult or impossible to swim or walk. I do however find it both rewarding to in some way hopefully help others in the world without thoughts of making a profit, except for keeping my brain active, and making friends that it is unlikely I will ever meet.
I have had a lifetime of travel both for pleasure, and work. That is not to say as funds permit I will not travel more, but I am content to live in a beautiful part of the UK. I do travel about this country small as it is with my caravan, and still find new things to see, and photograph. Photography being a long term hobby.

John (Britprius)

 

A small sample of your photography please sir.

 

There's a very small sample in my avatar of my home. I will however post a couple more if you wish in a few days.

John (Britprius)

 

love your avatar, as you know, but would prefer to be looking at it from the carribean, instead of from under six feet of snow.

 

Why would I need this? If it does indeed work to elongate the life of battery, by how long would it elongate?

 

There’s a lot of discussion about that here. But charger will balance battery so it will increase lifetime of the battery. And it will make battery capacity a bit better. Those are facts. But how much will it help, will pay for itself, or how often to use it, are complicated questions.

 

Too much drinking vodka in St Petersburg, I am afraid, my Finnish friend. No any other explanation of why would you think those are facts. None of them are.... and no logic there is...

Facts are:

1) NiMH battery pack in Prius does not have anything in its design to facilitate "balancing" while charging.

2) Charger connected with 2 wires to the most negative and most positive terminals of the series of NiMH batteries can NOT balance it. It can only charge it. If overcharged in attempt to "balance" then you are running into the risk of degrading your battery by overheating it. Overcharge is not recommended by manufacturer.

One may have read about balancing of LiPOs and think it is applicable to NiMH but it is not. Microchips (e.g. by Texas Instruments) which control charge/discharge of LiPO batteries in laptops battery packs for example can provide bypass to "deemed to be charged" modules while still allowing charging the rest. That is what battery industry call "balancing" [of LiPO].
That design is not required in NiMH packs and hence has not been incorporated in Prius.
EVs running on LiPo/LiFe batteries must have that type of design to prevent overcharging of individual modules in series.
Prius running on NiMH - does not need to....

With the same promis manufacturers of shampoo conditioners claim that if their product used regularly - your hair will be still there and still as good as when you were sixteen. Leftovers of the silver patches on my partially bold head make me thinking differently... Wisdom comes with age and experience...

As for preventive maintenance then Luscious Garage in CA for example found one usefull thing you can do to facilitate longevity of the pack - that is to maintain cooling system of the battery and clean the cooling fan regularly which could be clogged by all sort of things. (Saw clogged fans myself). They serve taxi Priuses 24x7 and if installation of grid chargers into taxis were of any good - be sure they would be doing that already. But they are smart enough to separate bullshit from pearls...

 

I haven’t been to Russia but maybe someday…

1) Yes perfect condition Prius battery pack doesn’t need balancing. That’s why Toyota didn’t build anything to balance it. But old battery pack can get out of balance for many reasons.

2) Yes overcharging is the only method that can balance battery like the one on Prius. But overcharging at low enough current doesn’t overheat it. Overcharging may deteriorate cells a slightest bit but if used rarely enough balancing effect will more than make up for that.

I know LiPo balancing is totally different subject and we should not mix it into here.

Shampoo conditioners are totally different subject also.

Decision to use or not to use grid charger should be based on does it give battery enough useful time to pay for itself (and installation +time) and I never said anything about that…

I’m pretty sure that you are the only one here that thinks that grid charger is totally useless.

 

Check out a Gen1 Insight or Civic Hybrid forum, grid chargers work. You can say they don't, but that doesn't change the fact that they do.

 

Be careful "Kiwi" your "like" average is falling quickly.

John (Britprius)

 

Picked up my grid charger from the post office yesterday, and will probably install it later this afternoon. My Prius has been in the body shop for a couple of weeks and my biggest fear was that the battery would have gotten so low as to throw a few cells way out of balance with the rest. So far everything is ok with it and I haven't seen any bigger difference in Vmax - Vmin, typically running between .08v to .12 volts just like it normally has been. I figured it was high time to go ahead and at least let it balance on the grid charger this weekend and then later on get a discharger from you guys Jeff.

 

Charged for about 24 hours solid after I had stopped a charge about 6 hours in (didn't want to leave the extension cords out Friday night because of pets and possible theft). I unplugged when I woke up this morning at what looked like a peak of 250 volts. Gave it about 20-30 minutes while I got ready for work. Started up and the SOC meter did a positive SOC drift to full green bars and spun the engine to bleed it down. I then coasted in neutral downhill to the main road to avoid regen on the way down, which by itself from 6 blue bars typically resulted in 8 full green bars, got on the main road and headed for I-81. Normally, after getting close to the interstate and bleeding off the battery during this part of the trip normally resulted in a bit of a negative SOC drift down to 50-54% SOC measured by Torque.

Not this time! Not even the rest of the way to work or the whole way home, which sometimes also results in it being pushed up to 70-74% SOC from coasting down some long hills back from work and bleeding that off by gliding with warp EV mode after reaching a comparatively level, albeit slightly downhill section of my normal route home through primary roads (not interstate). Looks like my battery definitely benefited from Jeff's grid charger! Haven't checked the voltages again yet, but I'll check them after about a week has passed.

 

BritPrius,
My very informal count of our alpha Engineers has you as quite supportive;
JeffD as tentatively supportive for specific cases,
and the remainder unconvinced (not against, but not buying.)

 

[deleted typo] Above is by no means representing any improvement in battery state of health at all. You just pumped a bit of a charge into partially depleted battery - hence battery started operating at the upper level of what I called "plato" charge/discharge curve. Start depleting it by using [before driving] aircon, radio, GPS, stereo etc and it will be back to where it was before quite quickly...

Statement: So called "SOC" measured by whatever scanner you use is telling you nothing about battery health.

I have run test again this Sunday on the NHW-20 battery - charging it with the newly designed version of 1.8A charger (isolated, high frequency, UL certified Japanese and Korean power blocks and components) and then discharging on the 5A load and charging again.

Purpose of the test was temperature management of the charger itself and stress load from full battery discharge all way up (8 temperature sensors connected to critical test points) plus 4 temperature sensors measuring battery temperature and one temperature sensor for the ambient temperature. Ambient temperature in the LAB was every electronic engineer's dream = +25 Celcius.
As part of the set up SOC measurements were also observed (not important for me though) as being captured by the scanner. SOC was changing from 60 down to ZERO although not important at all for my tests.
Point being: SOC itself was absolutely NOT representative of the battery health or battery dis-balance (dis-balance on pairs at the lower level of discharge was 2.33 Volts! [corrected typo]

P.S. test on the charger was absolute success. 1.8A @ 240V DC can now be replicated mainstream. Input 100-240AC 50/60Hz

I am releasing "Rescue Charger" based on the same schematic design with the 200-240VDC output @ 1A (1.2 Max). Two design versions: slick "Bond" style in the silver brief case with digital ammeter (don't like them personally but sacrifice for space) and "Geek" style in the HP low profile PC cases with awesome analogue meters.

Don't ask - not offering them for maintenance purposes -> "greed charger for battery improvement" - is nonsense IMHO. Rescue charger for depleted battery make sense....

 

that was typo - was running several non related reports at the time of posting.
... however, the point I was trying to make - do not rely too much on what the SOC is.
That test on Sunday on another battery -> delta V on pairs was 2.33Volts (Vmax - V min) when first pair reached 12V during discharge and SOC was ZERO. Capacity of that battery has not improved with multiple charging - it was around 3.9AH.

Right now there is another seems to be good battery I was asked to charge and test. It is good as car was driving well - but it was sitting for too long. It is now being charged @1.8Amps.
At the start SOC was only 10.After 1AH was "pumped in" SOC was 63, after 3AH in => SOC is 68,5 still taking charge @ 1.8 and modules have not reached 8.4v yet and temperature on modules have raised 1 degree above ambient (we have +26 Celsius now).

Later this week I am getting unbalanced pack as a gift for testing my new 2Amp chargers. Focus will be again on the proper cooling of the components but if anyone wish to have any metrics captured - do not hesitate to ask...

 

Here's something I've been wondering about with the grid charger rebalance. Assuming that you just do a simple slow charge to improve the top end balance, is it possible that you could worsen the bottom end balance.
The reason that I ask is that, though I believe that a top end balance may be useful to me (I get my SOC maxing out at the top end much more often than the SOC bottoming out), I suspect that the effect of a bad imbalance at the bottom end may be more detrimental to the pack (if the SOC bottoms out) than that of an imbalance at the top end. Does anyone have any ideas on this thought.

 

Uart,

When you slowly (and slightly) overcharge the HV battery (or individual modules), you are letting the weaker (lower SOC) cells catch up to the higher SOC cells (those dissipate the excess energy as heat so we must do it slowly). This lowers the possibility of reversing the lowest SOC cell in the string when deep discharging the HV battery. It also tends to increase the overall amp-hour capacity of the string as it is the weakest cell(s) in the string that determines this capacity.

JeffD
(the other Jeff, not Jeff652)

 

I totaly agree with JeffD above to the extent it could have been myself writing those words.

John (Britprius)