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Discussion Starter · #1 · (Edited)
A local inventor persuaded me to put a 12 volt NiMH battery into my 2001 Gen 1 insight - a bolt-in replacement when my 12v lead-acid battery wore out.

It's made of 30 heavy-duty NiMH D cells he purchased online, wired as 3 strings (in parallel) of 10 cells each (in series), so its voltage is almost exactly the same as a 12 lead-acid battery.

The cells are connected with about 10-gauge wire, and the joints are all soldered (I know the battery manufacturers don't recommend that). It's all in a plexiglass case with stainless steel bolts as terminals to connect to the car. It's quite light compared to a lead-acid one, but I haven't weighed it.

It cost about $300 but it was fun to try to save a bit of weight, and it is still working fine after 16 months and about 8,000 km.

I don't have a DC 'ring' ammeter to put on the cable going into it to measure how much current it draws when it is fully charged - because the voltage doesn't rise when full, the DC-DC converter can't detect that and slow down the flow.

He says that it should be good for 180 cranking amps, but I've never tested that with my new IMA battery always starting the ICE engine. It never gets below -10 Celsius here (about +15 F) so I'm not worried about low-temperature performance.

Here is his explanation of the voltage characteristics:
"Constant voltage charging is usually done with too high a voltage [for NiMH batteries of 10 cells in series].

I've done some tests and 13.75 to 13.90 volts is not only "okay" but IDEAL continuous voltage - they draw trivial current once they're charged to stay at those levels. The standard vehicle charging system is fortuitously 13.8 volts. So it happens that NiMHs are actually a better fit for vehicles than lead-acid - the voltage stays above 13 volts with the engine off, so headlights don't dim, etc, and you can turn off the engine at long lights, use lights and radio with the car off, etc, and save gas without worrying about the effect on the battery.

At 14.00 volts up, they keep drawing significant current once they're charged. The usual 14.2 volts is definitely overcharging if left on once they're charged."

There is no internal circuitry to balance the charges in the individual D cells - it's just all wired together, so presumably it will start to lose capacity as the cells age. I've no idea how long that will take.

More about this in the inventor's newsletter here: (see Car Battery Project)
Turquoise Energy Newsletter #36

I have a fuzzy photo of the battery attached.
 

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Cool project. :) 30Ah is roughly the same capacity as the stock lead acid battery.

With 10 cells in series, fully charged voltage is about 15V. That will never happen(or at least should never happen) with a charging system designed for lead acid.
 

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Cool idea and for your location that might be fine but I would worry about the heat at more southern latitudes which has proven to be a problem for both NiMH and Lithium batteries. The heat under the hood in the summer on a long trip is a lot higher than in the battery compartment. I was pleased that Chevy a battery climate control system in the volt that operates as the computer determines best (Car on or off). Have fun, RIck
 

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Cool idea and for your location that might be fine but I would worry about the heat at more southern latitudes which has proven to be a problem for both NiMH and Lithium batteries. The heat under the hood in the summer on a long trip is a lot higher than in the battery compartment. I was pleased that Chevy a battery climate control system in the volt that operates as the computer determines best (Car on or off). Have fun, RIck
Interesting. Another weight-saving alternative is the Braille battery. It can weigh as little as 6 lbs. for a 12V that fits the Insight. I have the 9 lbs. model installed in mine that gives more CCA than the 6 lb. model. Costs about $140US. Other Insight owners have used even cheaper off the shelf units smaller than the standard 24 lb. 12V Honda battery.
 

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I have to admit that I find all the discussion about weight savings pretty amusing.

Do you people also only fill your tank with $5 at a time, driving around with 2-3 bars of fuel? A full tank of gas weighs about 70lbs, after all.... :p

FWIW, just yesterday I got 52MPG over 700 miles @ 75-80mph.. in the rain... With an additional 680lbs in the car. About the same as I get with the car unloaded. ;) Admittedly, it would have impacted hypermiling numbers though. Lean burn just does not want to climb hills in what amounts to a 2500lb car.
 

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Eli I often drive my Insight full of heavy"junk"-but when you take it all out it seems so light!still put9gals. in every 570 mile on the local hills and corners.
ed
 

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One of the reasons I passed on the insight back in 06 when I wanted a fuel miser was the fact I weight half the cargo capacity. :cool:

I got the 2nd gen and its hauled lots of crap. Other than slowing acceleration and decelleration, I still get the same mpg once rolling. :)
 

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I have to admit that I find all the discussion about weight savings pretty amusing.

Do you people also only fill your tank with $5 at a time, driving around with 2-3 bars of fuel? A full tank of gas weighs about 70lbs, after all.... :p

FWIW, just yesterday I got 52MPG over 700 miles @ 75-80mph.. in the rain... With an additional 680lbs in the car. About the same as I get with the car unloaded. ;) Admittedly, it would have impacted hypermiling numbers though. Lean burn just does not want to climb hills in what amounts to a 2500lb car.
If you were out on the highway, the mpg drop would be barely noticeable; stop & go would be another story. I once had about 400# of water softener salt in my Prius and still got over 100 mpg on the 11 mile trip home from the store.
 

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If you were out on the highway, the mpg drop would be barely noticeable; stop & go would be another story. I once had about 400# of water softener salt in my Prius and still got over 100 mpg on the 11 mile trip home from the store.
Good point that. I do a fair amount of stop and go so my high school physics agrees with your point. To accelerate mass you need to overcome inertia. Once it's moving, less energy required to keep it moving. Hence, saving 100 lbs. or more does have minimal effect at steady speeds. City driving is where it matters most.
 

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To be fair, I didnt break 100 mpg til I cleared out all the crap, rear seat, passenger side mirror and anything else I didnt think was needed. :)
 

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Theoretically, the pack is operating much like the IMA battery in the Insight does. At 13.8V, the pack never comes close to fully charged.
 

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Its my assumption that having a battery that can take a charger faster would help mpg over a standard lead acid as when the battery reaches the right point the dc to dc converter shuts off faster.

Not sure about the i1, but the i2 also activates the dc to dc converter anytime you are regening too.
 

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Bottom line here is that the car hardly uses the 12V battery. My original battery after 10 years, had some dried out cells, would finally not hold a charge and was dropping out overnight when I finally changed it.
Just need something to keep the computers alive during the periods when the car is not used.
I have used 2 Prius subpacks in series at ~ 5 lbs, that is a pretty light weight solution.
I had one cell short in one of the prius subpacks, and that was where the problems started, as the dc/dc got the reduced voltage battery combo very hot trying to charge it.
This was not a parallel setup, which I would agree is a dangerous configuration.
 

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Funny you should mention that.

I have to admit that I find all the discussion about weight savings pretty amusing.

Do you people also only fill your tank with $5 at a time, driving around with 2-3 bars of fuel? A full tank of gas weighs about 70lbs, after all.... :p

FWIW, just yesterday I got 52MPG over 700 miles @ 75-80mph.. in the rain... With an additional 680lbs in the car. About the same as I get with the car unloaded. ;) Admittedly, it would have impacted hypermiling numbers though. Lean burn just does not want to climb hills in what amounts to a 2500lb car.
I just started putting $20 worth of gas into car at fill ups rather than filling to full ~$36. I found that topping it up I really did notice a performance difference that would last until I was down to three quarters or two thirds of the tank. Have been wondering if anyone else did this.
 

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Although I am glad I can filler up when ever I want I too find 5 galons to be the best balance between performance and fuel storage. If i am doing a lot of driving for that day, several days or weekend, then I filler up. :p
 

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I just started putting $20 worth of gas into car at fill ups rather than filling to full ~$36. I found that topping it up I really did notice a performance difference that would last until I was down to three quarters or two thirds of the tank. Have been wondering if anyone else did this.
Erik, if by "performance difference" you mean slightly more responsive acceleration, I have definitely noticed that when I get to the last 1/3 of the tank or thereabouts.
 

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Discussion Starter · #18 · (Edited)
To return to the original topic of this thread, this NiMH D Cell battery has been working fine for over 2 years now. I have left the dome light on for a couple of days and run it down to zero - twice. I don't really have any way to quantify its capacity or condition. it just works fine.

The inventor supplier is now making cases for these on his 3D printer, so his new design is smaller, with no soldering - the connections between cells are just metal contacts. He has asked me to switch over to one of those at minimal cost to avoid any problems with the soldering or friction between the D cells wearing out the cell casings. I haven't seen any sign of these problems but will probably do the change.

A local inventor persuaded me to put a 12 volt NiMH battery into my 2001 Gen 1 insight - a bolt-in replacement when my 12v lead-acid battery wore out.

It's made of 30 heavy-duty NiMH D cells he purchased online, wired as 3 strings (in parallel) of 10 cells each (in series), so its voltage is almost exactly the same as a 12 lead-acid battery.

......
 

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Bruce,
Happy to hear that your series parallel 12V replacement is working out, but beware.
If one of the cells shorts, the others will try to fill it, and magic smoke will be the likely result.
I had a 12V replacement made from 2 prius modules ,
http://99mpg.com/mikestips/themusefulpriussub/
and when one cell shorted, the dc/dc tried to charge it, and when the other cells got full, the whole thing swelled up and the sides of the cells blew out. Luckily I was just on a short test drive.
http://99mpg.com/blog/batterypacksexpose/whathappenstoapriu/
These were simply in series
Putting NIMH cells in parallel is usually not a good idea, as one string can drive over 100A into its parallel neighbor if a cell shorts.
Good luck
 
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