GOT HYBRID BATTERY QUESTIONS? ASK AWAY

i suppose it was just a google search to plug his new battery rebuilding business

 

He's busy asking all his friends for help with the questions in Posts 4 and 8...........

Post 4 I've already solved. Just curious now if an ASE Certified tech has seen it before. Seems like it would be a (semi?) fairly common issue. Post 8 I was (and still am) looking forward to an answer, as I run into that now and then. It would be good to be able to provide a solution.

 

My buddy at 2nd life Battery ran into that problem with a Tahoe Hybrid... He got it cleared by the age old practice of connecting the positive and negative 12v terminals together. Not sure that works with other vehicles or not.

 

So to help him promote his business , I just went to his FB page and asked why he ignored all our questions and if he treats his customers the same way?

 

By looking at this, can you tell if my battery is still okay?

 

Based solely on the screenshot shown, I would say your battery looks to be in good condition. The IRs look very consistent, which is a good sign. There's no individual module voltage that's lagging, but voltage doesn't always tell the full story.

With that being said, the individual module voltages are around 8.14, which means it was probably recently under charge. Sometimes that can hide a "weak" module.

 

Thanks for the detailed explanation. It's so confusing just by looking at the numbers

Any area or figures that I should be worried of if the next time I check my batt condition?

 

IR values are a quick way to see if something big is going on. You're currently showing 22s and 23s (milli-ohms) for block resistance values. That's the internal resistance of two modules connected in series, so each individual module would be about 1/2 that value. Those values are pretty typical for a early to mid-aged HV battery. Brand new ones typically read around 19-20. If you disconnect your 12v battery, the ecu will default to 19 until it recalculates. Module temperature will also cause them to change slightly. If you start seeing an outlier like a 24/25 it may indicate there's a module in that block that's developing a problem. A module with a higher IR will start exhibiting larger voltage dips under load. I've seen batteries working just fine when all 14 IR values were 28/29. Consistency is the key.

You can also get an app called Hybrid Assistant and Hybrid Reporter. That app will let you perform a load test on the HV battery using the AC system. The Reporter app will then take that data and graph all 14 block voltages on one chart. It makes it very easy to see if one block is lagging the others. This is a great way to track the health of the battery and gives plenty of warning if a block or two are starting to get significantly weaker than the others.

 

if I take a set of 4 modules for gen 2, parallel them and then Discharge/Charge cycle them, will they all eventually level out ?

Does the chemistry get 'used up' inside the cells or does it replenish itself with the moisture from the air ?

if a lithium ion battery is good for about 1000 charge cycles,
the NiMh inside a smaller usage range should be good for more ?

The ah capacity is 3.5 for one module so would that mean 14 ah for 4 ?

 

every module is slightly different, even relatively healthy ones. Also you need to study how each individual module discharges and recharges via three rounds of reconditioning to find the weakest modules. Doing the whole pack or multiple modules with the same charger is less thorough, less reliable of a pack in the long run.

 

Yet that is exactly what Prius bat mgmt does ...
Just charge them without regard to the needs of individual blocks ... right?

 

Yes, that's the only way to do it when you wire up 168 battery cells in a row... When they're brand new they're pretty much all identical, but as time goes by things start to vary a bit, especially the modules in the middle where heat is highest and also at the ends where high voltage first enters and exits the pack during peak amperage events....

 

at least they have a fan blowing at one end
(which the blades clog quite badly when people transport a cat /dog in the back seat)
(i wonder why the nissan leaf doesnt even have a fan for cooling its lithium pack) --
and so a 2ndary fan would have been nice and even a kind of liquid cooled (like the volt uses) management system would have made the prius legendary in longevity ... or so it would seem ...

 

There's an inherent problem with trying to charge multiple batteries in parallel. If 4 batteries are wired in parallel, there are 4 separate paths that current can take. In a perfect world, if all 4 batteries had the exact same characteristics, they would each have the same current flow through them. Unfortunately, it's not a perfect world. All four modules will be slightly (or more than slightly) different. Some will have higher resistance then others. There's no need to get into calculations, but you'll have 4 batteries, each with a different charge current passing through them. For all you know, 90% of the current may go into one module. Typical charging systems for parallel setups are a bit more complicated and have compensation circuitry.

Being connected in series causes the voltage to be additive, but ensures the same current flows through each module.

 

the story EricBecky gave of putting a charged pack in parallel with a depleted one where the higher gives to the lower and they balance out was the theory on that ...

i read that the R should be aroun 19milli ohms and as they age 20 or 21 ?
i dont think u can just take an ohm meter to measure that but have to get that info from an app like torque or maybe the techstream software ..

can you judge the life of a module with the R value it has ?

 

Correct.

Ohm's Law is very simple. I-V/R (current is volts divided by resistance). Over simplified, solving for R makes the formula V=IR and then R=V/I. But there's a little more to it since it needs some sort of a load to make a safe path for the current. I like this explanation:
Measuring Internal Resistance of Batteries - learn.sparkfun.com

 

In solar rechargeable systems, a calibrated resistance is needed to get accurate readings, so a shunt is placed inline to get that number.

I would think you could place a shunt in series between a load and a battery to get that value. If your shunt is a fixed, known value, and your load (a tungsten lamp) is a fixed value, then the only variable becomes what's measured off of the battery.

 

?

 

With lab grade instruments the resistance measures are incredibly helpful at determining module health, but with hobby chargers that measure resistance, as well as calculating resistance by hand via discharge data it's way more problematic, if not mostly useless. I'm still hoping I can figure out a way to get good resistance measurements without spending $20K on equipment. So far not much luck... If anyone knows a way that might work, please share!

 

Maybe an expensive hobby charger is not necessary. Most Ammeters have a precision inbuilt shunt, which can work with the low Voltage of a Prius cell. We just want to make sure it's also low Current, to limit inrush current to the Ammeter. Refer to the illustration (Basic Ammeter Use Worksheet - Basic Electricity), You could read the power flowing from a charger, then subsequently measure it under 'load' when the battery is connected to a light.

Because the Ammeter has a precision shunt, the value being displayed is the actual power provided from Charger. Irregardless of what its display might indicate, the value given by the Ammeter is what is flowing thru the circuit. There you have a known value, and can determine for how long you need to apply the charge. If you have 2 meters, the 2nd one could be attached to the posts of the prizmatic, to show you the Voltage at the same time the Ammeter is showing Current. That right there will tell you everything you need to know.

Once you've decided how long to charge, disconnect the prizmatic, let it recover.

Replace the charger with the Lamp, so now you can see the flow of Current under steady load.

Let the prizmatic rest.

Rinse. Repeat 2 more times.



While this may be time consuming, you will have determined the battery's capability (using fixed resistance and a fixed load). For testing the individual Prius battery, I would think a 6V 'lantern' type bulb would get you pretty consistent Loading. It may not be as fast, but it would be accurate.

 

For some reason this reply posted twice, but I can't find the option to delete the additional post. sorry.