Prius Batteries - How to make them work

[Mr. Mik]

edit: someone made the comparison about the nimh and lifepo4 and said that the lifepo4 doesn't tolerate overcharging. i think that is inaccurate, they are not damaged any more than nimh by overcharging, imo. similarly for overdisharging, because when you reverse a nimh, or lifepo4, both are useless afterwards. jmho

The 30Ah NiMH cells in the Vectrix seem to be tolerant to some reverse charging.

I have a few lowered capacity cells in the 102 cell string and sometimes the weakest ones get reverse charged for a second or two. Before I installed a manual BMS the same cells would have regularly been reverse charged for for several minutes.

They still have about 2/3 of the capacity of the best cells in the string!

 

[IamIan]

How do you measure the IR?

The crude method is to measure the change in voltage dV from the resting voltage to the voltage under a specific load.

More advanced methods include the use of AC current system in order to try and compensate for some of the non-ohmic effects that cause dV... the AC method is more complex to implement ... but has benefits.

edit: someone made the comparison about the nimh and lifepo4 and said that the lifepo4 doesn't tolerate overcharging. i think that is inaccurate, they are not damaged any more than nimh by overcharging, imo. similarly for overdisharging, because when you reverse a nimh, or lifepo4, both are useless afterwards. jmho

I've made that comment about tolerating abuse.

LiFePo4 will not tolerate abuse any were near as much as NiMH will ... I've tested both myself ... and read others tests as well... LiFePO4 ... must have a BMS to protect them from the abuses that NiMH are often just expected to take regularly.

Let's take a look at each part just a tiny bit... great detail would be too big... this post is big enough already.

Over Discharge:

I have pulled NiMH cells down into voltage reversal several times ... it does damage ... but it is not an instant death sentence for NiMH ... I have even drained individual cells so far down that after resting for ~12 hours still show less than 0.2V per cell... and they still will recover ... sure they take damage from abuse ... but they are far more tollerant than LiFePO4.

Try to drain a single LiFePO4 cell down to 0.2V resting voltage for ~12 hours ... if it works at all ... it won't take that abuse nearly as well as a NiMH cell will... and my money is that there is a 80+% chance the LiFePO4 battery won't come back at all... Try pulling a LiFePO4 battery into voltage reversal ... if the cell will even let you... and see how well it does afterward .... it won't be nearly as well as a NiMH cell will take that abuse.

Over Charge

The Resting voltage of a fully charged NiMH cell is never more than 1.4V per cell... NiMH cells are often overcharged using CC and taking advantage of their tolerance for this abuse... Try Charging a LiFePO4 battery under a Constant Current until the Voltage levels off ... as in don't switch the LiFePO4 over to the Constant Voltage part they are always finished off at... If you tried to charge a LiFePO4 battery with this kind of regular abuse ... there is no way it would take the hundreds of charge cycles that NiMH cells take under this abuse.

If we wanted to be as gentle to NiMH as we are to LiFePO4 ... we would only do the CC up to 1.4V per cell ... then like the much more delicate LIFePO4 ... we would switch over to a Constant Voltage to top off the rest, until the current level dropped bellow a certain amount ... we would have NiMH BMS that limited current per cell ... and minimum voltage per cell to never go bellow 1.0V... but we usually only see these type of BMS and delicate treatment of batteries ... when they are not the far more tolerant NiMH cells.

I can put a NiMH cell on a Constant current charger of ~C/20... and after is has taken over 3 times the rated Ah of the cell , it will be warm ( maybe even hot ) ... but I can do that to NiMH cell hundreds of times before I lose ~20% of the original rated Ah of capacity ... Try to over charge a LiFePO4 battery like that ... I doubt you will be able to get even 20 such cycles before the LiFePO4 shows serious service life damage from such over charging abuse.

------------

This is not to say LiFEPO4 don't have benefits ... they definitely have many benefits ... but being tolerant of over-charging and over-discharging abuse ... are not among the things LiFePO4 do better than NiMH.... this is why LiFePO4 systems often include BMS monitoring down to the individual cells... while NiMH far more rarely include this level of BMS complexity.

For example ... my 2000 model year Honda Insight on the original ~9 year old NiMH batteries ... is only monitored by the OEM system for voltage once every 12 cells ... for temperature 4 probes for the whole 120 cell battery pack ... for current 1 probe for the whole 120 cell battery pack.... no OEM method for balancing SoC among the 120 cells ... etc... and yet when I pulled the battery pack and tested it ( a few months ago ) ... it still showed ~90% of the original Ah of capacity after ~9 years of abuse taking 15C discharge rates ... 7C charging rates ... in bakes in the summer , freezes in the winter ... etc... NiMH Rav 4 EVs have been on the road even longer under standard NiMH abusive conditions / treatment.

---------------

Of course you don't have to believe me ... you could go out and run a few tests yourself ... if you don't' mind destroying some new batteries.... as used batteries are not a control test , they bring the history along with them... and thus would make for a bad test.

Buy a new NiMH battery ... put a small load on it ( nothing higher than C/2 as we want to really drain the battery down as much as we can ) to pull it down to a 0V condition ... let it sit like that for 12 or more hours ... then force a C/20 Constant current ( CC ) charge rate into it until you have applied 3 times the rated Ah of capacity ... then do a discharge test and measure to see how many Ah the battery will still give you.

Then put a LiFePO4 cell ( like from A123 power tools or others ) under the same abuse ... and repeat the same experiment ... ( you might have to bypass a power tools built in pack safety circuits to even be able to pull it down to 0V ) ... then after it has sat for 12 hours after being discharged to 0V ... over charge it with a C/20 CC rate ignoring the batteries terminal voltage and just keep on forcing in that C/20 CC charging rate until you have applied 3 times the original rated Ah of capacity ... then measure the amount of Ah you get from the LiFePO4 battery pack... If you did bypass the safety IC in order to put the LIFEPO4 battery under this kind of abuse ... I give the LiFePO4 battery less than a 10% chance of taking even 3 such cycles as well as the NiMH battery will.

 

[GTA1]

Toyota debated the use of Lithium batteries inside the company... throwing quite a bit of the finest R&D minds at the issue, and ended up rejecting Lithium.

Now, for automobile considerations, there is the sheer problem that Lithium do not scale ---- there is not enough lithium in the world to support more than a minute portion of the auto fleet changing over.

That may or may not be an issue with e bikes.

However, the cost spread between lithium and Nimh remains an issue.

I am, quite frankly, impressed by how far Toyota has taken this technology.

 

[Mr. Mik]

How do you measure the IR?

The crude method is to measure the change in voltage dV from the resting voltage to the voltage under a specific load.

More advanced methods include the use of AC current system in order to try and compensate for some of the non-ohmic effects that cause dV... the AC method is more complex to implement ... but has benefits.

Thanks, but I meant you, personally! Which method did you use?
Sorry I was not very clear with my question!

 

[icecube57]

At what C rating are these prius packs rating at. I tried doing 40A discharging and im coming up around 4AH before it goes flat. It seems that the NIMH only deliver about 60--65% of their actual AH capacity under high loads. From my understanding that some battery manufacturers use a c/4 rating where they use 1/4 of AH avaliable which ia 1.6A and discharge it. Thats how they are able to get full capcity in some cases. I know my Tenergy NImh packs dont deliver full capacity at high load. I get about 60-65% of the capcity when pushing those packs. They compare to lead acid in performance and capcity but without the weight. My 12v 16AH Nimh pack weighs 8.8lbs. Its supposed to be 16.8AH but i get 11-12AH at 3-4C. But looking at sealed lead vs nimh... my nimh deliver 60% more capacity for the same weight....even though im not getting 100% capcity. Also how does a continuoous discharge affect capacity vs High C short bursts or Low C long discharges. How does resting a cell affect capacity. Allowing the cell to recover for several seconds or minutes before discharging more. The short burst put a high load but when you average the C discharge for the run its often less that 1-1.5C for most common setups.

 

[lesdit]

I guess that the primary design goals for these were for high current bursts for a few
seconds at a time. I don't think the prius does high current for sustained periods. Another
design consideration would be to never discharge all the way, and never charge all the way either.
They had the luxury of these design parameters since the cells were purpose built for the client,
Toyota. For the price, they are still pretty good, IMO. I'm running a globav Ev 36 volt bike with
5 of these. No CA metering as of yet, but they seem pretty good to me.

 

[gasfree]

Hi lesdit,
How long does your pack last for? Do you pedal along or do you just throttle all the way?
I am going to do a run tomorrow with the one I built (6cell pack), and hopefully it will get me to work.
I have a 14km one way trip so we will see what happens. I have a 36v nicad just in case.

 

[icecube57]

I was doing bench discharge tests. The packs are able to deliver the 40A i was asking for no problem up to about 4AH. The thing is this is a continuous load with no rest. With ebikes under normal setups we pulse and glide or do low steady current. Since im asking such a high discharge rate of 6C i think its reducing the capacity. I havent charged back up yet but I am going to do a C/6-7 perhaps maybe lower discharge test to see if all the capacity is there.

Im tied up doing a discharge on my Nimh Tenergy pack. Im doing C/14 discharge which is near 0.3A. If I cant get 80-90% capacity i will be disappointed.

I will try the same thing with the prius packs to verify true capacity.

If i can get 4AH out of this packs it will equal 12-15 miles for me because i normall get 3 miles per AH at 5A continuous at a steady 20-22mph on level ground.
Im going to use this on a cheap 36v sla bike and run it at 5s 2p. It should get 8-10AH at 36v.

 

[lesdit]

I have yet to do a full drain test. For easy local trips, 4 miles at full throttle seems ok for it.
I guess I'll try an all uphill test away from my house, so I can roll back down after it dies.

Hi lesdit,
How long does your pack last for? Do you pedal along or do you just throttle all the way?
I am going to do a run tomorrow with the one I built (6cell pack), and hopefully it will get me to work.
I have a 14km one way trip so we will see what happens. I have a 36v nicad just in case.

 

[gasfree]

Well I charged my pack for about 3 hours. Unfortunately I only have one charger so I can only charge one string at a time. I rode from my house to work which is about 11 miles away, with couple of hills in between. My top speed was 48km and I averaged about 38km with some light pedalling. The battery read 49 volts when it was fresh.
Unfortunately for me I forgot to bring the power cord to work so i had to rig something up to do a partial charge. Overall though I am happy with the performance it delivered and my next step is to parallel it with another pack to get more Ah. That should help out alot more. Anyone have pics of their packs and how you charge them. I will post my really ghetto setup up when I get home later in the day.

 

[gasfree]

Well I did my ride back from work yesterday. the starting voltage was 50 since it had been just charged. for half the ride it was pretty much flat with very small downhill slopes. I do notice that it jumps to 1400watts when I do full throttle even though I am pedaling along with it. The hardest part of the stretch was crossing the bridge its about a mile long and its about a 10 degree slope. The battery died about mile from home. Seems to be pretty good I just need to add another pack. Oh yeah when it died the voltage dropped straight to 30. top speed was 54km & avg was 38km. I will ride it again tomorrow. I am having back spasms today so I will have to drive. =(

 

[gasfree]

Well here is my ghetto setup for charging. Playing with electrical items is a new thing to me still. So after being shocked and burned I am still here trying to figure out how to get it all to work together. I am still waiting for my laptop chargers to arrive so currently I only have one. It's a pain in the ass to charge them string by string so I figured parallel charging them together would be the next step. So far so good. Here are some pics of what it looks like. I had an incident a few minutes ago and all I saw was a huge light. Good thing nothing happened.

My sad charging rig. Any pointers on how to make this better would be greatly appreciated. Pictures work too =).

my oops....

here I was curious what the setting was and this is what made the bright light, not trying that again.

Lost a bit of the tip but still works.

Oh yeah for got to add that I am gonna try to hook them up in parallel so I will have a 43v 13Ah pack of the charger they tend to read 49 but it drops off pretty quick. I need something with more torque for hill climbing abilities. Oh yeah I am running it on a 406 motor good for flat roads.

 

[gasfree]

here is the results of my quick test ride. I need new brakes I think I have warped my disc brakes.

 

[gasfree]

Out of curiosity has anyone used a lifepo4 charger with the prius? I briefly tried it out today and it seem to work. I don't know if there is any side effects. I only used it for about 5 mins and watched it output about 4ah into a 6 pack. I am curious to know if this is similar to using ibm laptop chargers in string since they are used to charge lithium ion batteries. Any thoughts? Hope I don't hurt myself or anyone else while I experiment.

 

[Lapwing]

Why you buy a used Fluke 87 or similar off E-bay! :?

Blew up a cheepy chinese once - once is enough.

(time to do laundry?)

 

[nedfunnell]

Hi Everybody,
I got here via a google search. I'm a hobbyist/college student looking to make an electric bike. I'd like to use some Prius batteries- I accumulated a bunch of stats a few months ago online, but it is great to hear that some people are doing some real world work with them and they appear to be pretty resilient.

One key interest of mine, however, is high-current performance. I have a very large motor and I would like to get full performance out of it. For this, my current idea is to use 4 parallel sets of 6 battery modules, which would put me at 42.3v @ 19.5Ah. This would use 24 modules, so almost one whole late-model Prius pack. If I assume a 10C discharge rating, I'd get 195A- pretty close to my 225A goal, which is the current limit on my controller, which is a Curtis 1204-410. I'm using a PMDC motor.

You might have guessed that this bike is more for fun than commuting- I live on a small campus, so my rides will be less than a few miles each. My campus is hardly a mile in perimeter. Because I don't need much range, and because I happen to own a huge motor, not to mention that I am a youngin, it is more important to me to have peak power than maximum range.

Now, one point of confusion on my part- I don't understand the generation terminology that you are using. As I understand it, the first generation Prius was released only in the Japanese domestic market and we won't see any of those batteries. Second gen Prius is the Prius we all know here in the US, and the third gen Prius is new for this year- surely everyone here is not using modules from brand-new Prii, right? I seem to remember a switch in the battery in the model year, but I don't remember exactly and I didn't write it down. Could someone enlighten me as to which years of Prius have the desirable batteries?

Edit: The chart on this site: http://www.toyotapriusbattery.com/ cleared me up. 04 and newer. Got it.

OK, now on to another few questions- shelf life. How long can these batteries have been sitting at the scrapyard and and retain their viability?
I am considering homebrewing my own charger- I have a BIG multitap transformer from a welding machine I dismantled to get pretty close to whatever AC voltage I want, I'll rectify that to DC, and my thought is to use that as a voltage source, charging the modules with a series resistance. I am not yet sure how I will manage charge termination- ideas?

 

[fechter]

Hmm.... nice job with the ammeter. I think everybody had done that at least once. :wink:
I guess the batteries can put out more than 10 amps.

 

[lesdit]

I had some sitting for a couple of years, they still showed 7.1 volts !

OK, now on to another few questions- shelf life. How long can these batteries have been sitting at the scrapyard and and retain their viability?
quote]

 

[gasfree]

Yeah I believe they put out about 60 -75 amps. My controller only goes to 35 so I can't really verify it.

 

[icecube57]

I had packs from a Gen II Prius I pulled 40A continuous for about 4.5AH straigh with no problems. Charging is just a bitch. A simple circuit should be made to either terminate charge after X amount of hours depending on the pack AH and charger or have something that senses voltage of 8.3-8.4 and terminate charge.

 

[gasfree]

I had packs from a Gen II Prius I pulled 40A continuous for about 4.5AH straigh with no problems. Charging is just a bitch. A simple circuit should be made to either terminate charge after X amount of hours depending on the pack AH and charger or have something that senses voltage of 8.3-8.4 and terminate charge.

what do you use to charge your prius cells? I have yet to find a way to get more than 2.2 -2.5 ah out of them.

 

[icecube57]

You may just have a super old pack. I used regular tenergy nimh chargers and charged them to 8.4. I charged in parallel also. It takes a while but i was gang raping them with 2-4 chargers in parallel at almost 8A for the entire bank of 9 packs i had. Even at those amps i wasnt near 1C charging.

 

[gasfree]

Yeah I think my pack might be old. I charged it for just over 3 hours yesterday with my lifepo4 charger. I have that one set to 58.1 volts. I was barely able to get 3Ah of use after. But something is better than nothing. I might ask this bodyshop for another complete battery. They service taxis all the time I might get lucky and get better cells. Where did you get the tenergy charger from? I notice that they also cell battery packs but have no prices up.

 

[icecube57]

I got my Tenergy Chargers from All-Battery. They have a NIMH charger that has a temp probe. I have not charged the prius cells with that charger but im sure if you sandwich the prob in between the cells it might terminate charge properly. The chargers dont detect Delta V but they might detect the rise in temp. The charger may look at one or the other or perhaps both. Im not sure you would have to call All-Battery up and talk to them. I did a review on their Tenergy Sub C Nimh High discharge packs. The 12v 4200AH side by side packs I bought are only good for about 2.5-3AH. You could probably use a single pack and draw 40A but it would sag down to 10v or less. I put 4 in parallel to discharge 40A safely while maintaining 11+v during most of the discharge. So that should give you an idea on how well they operate. I bought 4 and use it as a booster pack. It works out fine. But i wouldnt use them to build a main pack. I would rather use Bosch Fat Packs.

 

[Mr. Mik]

Hi,

can anyone tell me what this label on a Prius battery means?

This is the battery:

What battery is this, how many cells are in it etc?


Does the label mean it has already been recycled, or that it should be recycled?

Thanks!