Honda Insight Forum banner

1 - 15 of 15 Posts

·
Premium Member
Joined
·
4,389 Posts
Discussion Starter #1
This hot subject can only be determined by lots of careful research and test. As I stated in the other thread, the additional batteries would be a great way to replace a dead insight pack, or to add extra capacity for heaver MIMA use. The fooling of the battery SOC ampmeter has a good chance of working, but if it does not, the fall back position is to fake out the BCM completely. A string of resistors with taps where the subpacks now connect would always look good to the BCM, and a fixed voltage generated by an external battery monitoring system that replaces the present current signal would allow a complete fake out of the BCM. The over charge and subpack monitoring would be done in the external micro based MIMABCM controller, and could stop charging when full by simulating a fully chargeg pack to the old BCM, and could make the SOC meter correctly indicate the SOC of the larger pack, by sending a voltage to the SOC measuring circuit of the old BCM to fool it into showing the correct charge on the SOC bargraph.
I have taken some high resolution photos of the prius BCM boards. If someone wants to help with this project, they could try to locate data sheets for all the key parts, and we could reverse engineer the thing so that the prius BCM in the recycled packs can be used in our booster packs to monitor the batteries.
 

·
Registered
Joined
·
38 Posts
Not experienced enough to be much help, but you should definitely post all your research and pictures, sounds impressive :)
 

·
Premium Member
Joined
·
278 Posts
Hi Mike,

I guess your first port of call should be here:

http://www.ctts.nrel.gov/analysis/pdfs/31306.pdf

This was a very useful and detailed investigation and comparison of the Insight and Prius battery packs by NREL. Included are much info on temperature performance, current, SOC, management etc. possibly quite useful for your project.

The next big resource could have been the Prius+ group files, who are attempting something similar and are keeping all of their findings open to anyone. A lot had been researched in terms of other batteries to use to add to the capacity of the OEM pack too. However, their work concerned the '04 Prius, while most of the junked Prius batteries you will likely find will be 2001-2004. There were at least 3 types of Prius battery used, the first (Japan only?) '97-'00, then the '01-'04 which I think was the only type the US got, though not sure of these dates so can't be sure. The '04 got quite a different pack to the previous shape Prius, a smaller pack (1.3 vs 1.8 kWh), but with higher power density (~1,300 W/kg) and more aggressive (ie wider range of) SOC use.

More practically speaking, a link I’d need to find for you is the website of a German guy who has analysed everything about the battery performance of his ’01 Prius and made it all available online – can’t find it yet but will keep looking. John’s Prius site has some useful background however:
http://john1701a.com/

Will keep digging…. :)
 

·
Premium Member
Joined
·
278 Posts
An overview of the findings of the PriusPlus group who are attempting something similar:


(BTW, most people on here may have picked up on the fact that I am a big fan of lithium, so here is my favourite quote from this review!

"Given today’s cell availability, NiMH technology is just as hard and expensive to implement as LiIon, but with 1/2 the value." :wink: )




1. The state of CalCars’ NiMH battery pack


1.1. Procurement status


1.1.1. With the exception of the Saft NHP10-340, which is not in
volume production, and possible Chinese cells of unknown quality,
we have found no appropriate cells


1.1.2. Even huge battery companies like Saft and Cobasys produce
only one or two sizes of high-rate-discharge cells (Cobasys’ are
too large and heavy for a PRIUS+).


1.1.3. A custom D cell pack has been our fallback possibility


1.1.3.1. We have found a promising technology (anodized aluminum
tubes) for building a thermally acceptable battery pack from D
cells, but . . .


1.1.3.2. 3-4 parallel strings of (176-182) cells are required, and:


1.1.3.2.1. Lots of electronics are necessary to assure no
problems occur due to paralleling NiMH strings, to assure that
no cells are reverse-voltaged due to capacity and charge
balance variations, to detect and minimize charge imbalances,
and to detect end-of-charge. This discipline is of the same
order of complexity and expense as that required for a LiIon pack.


1.1.3.2.2. All NiMH D cells that I’ve tested have double their
expected internal resistance. This means that to better the
Prius’ OEM battery in this respect – required to avoid an
increase in hybrid gasoline consumption with the PHEVs
additional weight – will require four parallel strings of one
of the three best types of D cells tested, plus at least one
string of Maxwell D cell supercapacitors in parallel.

This solution will cost over $10,000 plus the control/monitoring
electronics, as two of the three usable types of D cells cost $10.71
each, the third has 15% less capacity than the others, and each string
of supercapacitors costs $2400.


1.1.3.2.3. Charge imbalance solutions require careful
monitoring of substrings of 8-13 cells. If individual 1.2V
cells have low capacity or get out of balance with their
peers, little can be done beyond reducing the imbalance via
additional overcharging (very limited without shortening the
battery’s cycle life) and/or reducing the effective capacity
of the pack.


1.1.3.2.4. Thermal management of the pack is critical, as


1.1.3.2.4.1. Charge imbalance is greatly increased by
temperature differentials between cells.


1.1.3.2.4.2. Cycle life is halved by every 10 degrees C
above room temperature during operation.


1.1.3.2.4.3. Double the expected internal resistance means
double the pack’s creation of heat.


1.1.3.2.5. Supercapacitors may be a partial solution to the
internal resistance limitations, but . . .


1.1.3.2.5.1. They have not been tested yet for effectiveness
or how many strings are required in real-world driving
situations


1.1.3.2.5.2. They add cost, weight, and volume: per string,
$2400, 25 lb, and half the volume of a string of NiMH D cells.


1.1.3.2.6. After all the work and expense of designing and
custom building such a pack and its electronics, there is no
guarantee that it would work well and have a decent cycle life.


1.2. The auto companies may be moving toward LiIon packs for their
hybrid vehicles


1.2.1. Why I think so


1.2.1.1. LiIon cells have around twice the specific energy of
NiMH cells, and triple the cell voltage.


1.2.1.2. There are now LiIon cells capable of high rate
discharge and high rate intermittent (regen braking) charge


1.2.1.3. Thermal runaway problems and propensity to explode have
been solved for small, quality battery packs.


1.2.1.4. There are companies touting their LiIon systems as
hybrid batteries.


1.2.1.5. Existing hybrid vehicles are, due to the automotive
development cycle, from designs at least six years old


1.2.1.6. There are rumors of LiIon-based hybrids in the pipeline.


1.2.2. What it means


1.2.2.1. The NiMH chemistry is more of a lame duck technology
than we imagined


1.2.2.2. At best, only NiMH cells that are already in automated
volume production can be expected be available in the future.


1.2.2.3. Future price reductions or product improvements are
unlikely.


1.2.2.4. Product discontinuations must be anticipated.


1.2.3. What it means for CalCars


1.2.3.1. Given today’s cell availability, NiMH technology is
just as hard and expensive to implement as LiIon, but with 1/2 the
value.


1.2.3.2. LiIon safety issues for vehicular battery packs either
have been or are soon to be solved, probably in various
industry-acknowledged ways.


1.2.3.3. By the time CalCars has tested an NiMH PRIUS+, auto
companies will most likely be viewing LiIon technology as
mainstream, too.


1.2.3.4. At this point, it apprears to make most sense to skip
NiMH altogether.
 

·
Registered
Joined
·
1,819 Posts
"At this point, it apprears to make most sense to skip NiMH altogether."

Which means you've completely missed the point of what I, at least, hope to do. I'm not interested in spending X thousands of dollars for a bunch of new Lion cells (or new NiMH cells, for that matter). I want to pick up a pack from a wrecked Prius, at a cost someone mentioned as about $500, and play around with making a useful and CHEAP additional and/or improved replacement pack.
 

·
Premium Member
Joined
·
278 Posts
Hi James, yes you're right, the Lithium discussion is probably off-topic for this thread - will start another one on this some other time. Included the info because Mike had been looking into the Valence LiIon as an alternative (is about $1,650 per kWh - about twice the cost of the junked Prius option, but new and half the weight and size).

However, as cost is the main issue for you (and presumably most people) will stick to topic and try to come up with some more Prius stuff! :oops:

Still can't find that German guy's site.... :?
 

·
Premium Member
Joined
·
4,389 Posts
Discussion Starter #8
Thanks Clett
The overview is very useful as it saves a lot of time, and gets all the information in one document for future reference. The valence batteries were and would still be my first choice as a battery replacement, but it will be a few years before the price will become competitive enough to be practical.
The best thing about the prius pack is the potential of doubling, or tripling (retention of Insight pack) the capacity of the original pack while reducing the cost of replacement.
A great way for someone to help in this endeavor would be for someone to start searching for used prius packs and see how available they really are, and how much they really cost. We have an example of one, The pack that Mr Dunn sold to me for his cost. He indicated that the used packs ran from $600-$1200, but without finding several more and confirming their availability, we cannot be sure.
The parallel battery safety issues and cell imbalance issues must be carefully considered in any pack replacement, but are not unsolvable. In the extreme solution, Microcontrollers with built in A/D converters, could be placed on each subpack of 7.2V. Opto coupled serial communications to a central BCM like controller could monitor the subpacks more carefully than either the prius or the Insight batteries are presently being monitored. These little processors and a few components would cost less than $3 per subpack, and could do individual subpack balancing if needed. The NRE (Non Recurring Engineering) cost would be quite high to develop the system, but it would be a flexible battery control and monitoring system that could easily be transported to any future chemistry or pack size. A lot of the current R&D in series battery pack design for hybrid and EV use is moving to this active battery management concept.
The prius pack as used in the car, like the Insight pack is a single series string so the battery monitoring task and related safety issued are less stringent than any parallel pack design. I have no doubt that the task of simply dumping the Insight D cell pack, and putting in an equivalent Prius single series string could be accomplished quite easily, and would involve mostly the repackaging of the prius subpacks into an Insight equivalent sized box and the design of an effective cooling system. All of the limits and cell reversal functions of the Insight BCM could port directly to the nearly identical capacity prius pack.
Nemystic has indicated that on his daily commute, he has improved his fuel efficiency by a factor of 15%, while never drawing the pack much below the 70% charged condition (not a lead finger like me), so the single pack replacement with Prius subpacks for a hypermiler driver may because of weight and the retention of the storage well and all safety's be the smartest way to go. We need to get more MIMAs installed before we will know.
 

·
Registered
Joined
·
1,819 Posts
"...the single pack replacement with Prius subpacks for a hypermiler driver may because of weight and the retention of the storage well and all safety's be the smartest way to go."

It's a bit different for me. I'm not a hard-core hypermiler - I mean, mileage is good, but so's performance :) Basically I have two long climbs - about 2500 and 4000 vertical feet - that I do frequently. I'd like enough battery to have assist available all the way up, and recharge all the way down.

I figure that's roughly 1.5 to 2 times the Insight pack, since with trying to minimize assist I drain the pack in about 1500 ft, and get full charge about 2000 ft into the descent.

So options look like 1) add-on pack using about 20 of the 38 cells in the Prius pack, or 2) get 2 more cells, and replace the Insight pack entirely. Sounds like #2 might be the easier technically, since you'd just fake the Insight's control signals with a new BCM.

Once I get back home and get Mima installed, probably July sometime, I can maybe look around for a used pack, and do some directed experimenting.
 

·
Premium Member
Joined
·
278 Posts
Right, have had some more success unearthing Prius battery resources.

First is a beauty: http://ozgrl.com/priusparts.htm

Self explanatory really!

Second is a thread from Priusonline discussing the average cost of salvaged batteries: http://www.priusonline.com/viewtopic.php?t=1842

Consensus was about $300-$850 vs $6,000 for new!

Still trying to find that German guy's site with all the technical stuff... may actually be better to get the manual in .pdf form from Toyota ($10 per day from their website).
 

·
Registered
Joined
·
88 Posts
What about the addition of a 2nd Insight battery pack?

I imagine these are even less available used, but must be available somewhere?

Also, what of the Accord's battery pack? Is it the same size as the Insights? I'm fairly certain it uses the same 144v system, but perhaps it has more capacity for the heavier car? (I belive it's motor makes about 150% of the Insight's) ~10kW vs 15kW.

For that matter,(at the risk of getting off-thread) I wonder if the Accord's IMA motor could be used in an Insight?
Too new to find many yet I'm sure, but perhaps this could be a good mod once affordable?

Thanks,
--Ash
 

·
Registered
Joined
·
182 Posts
Mike Dabrowski 2000 said:
The parallel battery safety issues and cell imbalance issues must be carefully considered in any pack replacement, but are not unsolvable. In the extreme solution, Microcontrollers with built in A/D converters, could be placed on each subpack of 7.2V. Opto coupled serial communications to a central BCM like controller could monitor the subpacks more carefully than either the prius or the Insight batteries are presently being monitored. These little processors and a few components would cost less than $3 per subpack, and could do individual subpack balancing if needed. The NRE (Non Recurring Engineering) cost would be quite high to develop the system, but it would be a flexible battery control and monitoring system that could easily be transported to any future chemistry or pack size. A lot of the current R&D in series battery pack design for hybrid and EV use is moving to this active battery management concept.
I agree that it is ideal to monitor cells (or sub-packs) individually, and ideally to also have an active cell balancing circuit. That's true whether or not you have parallel packs. But I think it's possible to deal with the parallel pack issue by looking at the fundamental issue--the potential for one pack to charge the other without the control over that charging process that is normally in place.

The obvious thing is to make sure the packs are at the same voltage before you connect them together. Doing otherwise could result in unlimited current out of one bank into the other.

If you get them to the same voltage, and then connect them, and they are identical, they should track perfectly from there on. The question is what if they are the same chemistry, but different cell designs, or different temperatures, etc. Of course you can try to keep the temperatures similar, but it won't be perfect, and the influence of the cell design is more complicated.

But regardless of how likely it is to have trouble, or how well you do at avoiding it, it would be nice to include protection to avoid damage if there is an imbalance. We could do this by putting a separate current sensor on each pack. That's two sensors instead of dozens to monitor each cell voltage. The net current in or out of the combined pack is i1 + i2. Then an analog circuit or a uP could be set up to look for a fault condition defined by max(|i1|, |i2|) > |i1 + i2| + ia, where ia is an allowable rate of charging from one pack into the other. Then of course there needs to be some kind of contactor that would disconnect one of the packs in that case. Then you would need to carefully get the voltage back equal before connecting them again. Ideally the fault would happen rarely or never. If it turned out to happen frequently, then we'd need some kind of charge controller that would step in and do that equalization job when needed.

Back to the issue of cell balancing within the pack, there's a very elegant way to force cell balancing without needing to monitor each cell, and without the dissipation that occurs if you try to passively balance them with resistors.
http://www.freepatentsonline.com/patent ... 710504.pdf

Ironically, if you were to implement that on the existing pack, you'd likely extend its life, and void the warranty on the pack!

Charlie, who alternates between thinking he should treat his pack gently so it lasts forever, or use it intensively so as to wear it out before the warranty is up.
 

·
Premium Member
Joined
·
4,389 Posts
Discussion Starter #15
I like that switched capacitor system, it solves a lot of problems.Tie that type of charge transfer with a micro based individual 7.2V subpack charge controller, temperature monitor(the subpack powers its own microcharge manager.) An opticaly linked LAN from each subpack charge controller to a master micro, that communicates with all three packs individual subpacks, and you have an expandable subpack active balancer. It is possible, but lots of NRE to get there. I also believe some people are working on this right now, as I was approached last year by someone wanting me to design just such a system, but at the time I was involved in another big project and had to decline.
This is real interesting for me, I have enough prius packs to make up a dual 144v parallel pack, but I need to stay focused on MIMA or I will further delay it.
This is the next Insight project.
Parallel projects have the same increased complexity as parallel battery packs. Always easier to keep them in a single string.
 
1 - 15 of 15 Posts
Top