I'm interested in increasing the battery capacity of my 2000 Honda Insight, and FEH battery packs are a cheap source of NiMH cells.

I understand the FEH battery is 50 sticks of 5 cells each * 5.5Ah, right? Honda's is 120 cells * 6.5Ah, so if I parallel each half of the FEH pack, I should have an 11Ah pack with a voltage that is close enough for my inverter to run off of.

It would probably be a "BYOBMS" project that would involve tossing out the Honda battery. How many voltage taps does the FEH pack have, and does it use a PTC for temperature monitoring? Is the battery case too wide to fit in an Insight, and would it respond well to being sawn in half?

I could go with 40Ah of lithium for $3000 in batteries, or 11Ah of FEH NiMH for $300. I prefer NiMH because most of your cells will last 20 years or more. That, and a NiMH BMS is so much simpler.

If you can answer a few of my questions - thanks!

 

I don't own a FEH but as far as I know it's a 5.5Ah 330V pack. So, 330V devided by the 1.2V nominal Ni-MH cell voltage means there are 275 cells.

Li-Ion cells are 3.7V/cell nominal voltage, not 1.2V/cell like a Ni-MH cell is. A big difference!

 

Wikipedia says it's 250 cells, which means they used 1.32Vpc for the nominal voltage. That's probably pretty close to the actual resting voltage.

You can do a Google search on Peter Perkins' 40Ah PHEV Insight to see how he's using 50 lithium cells in place of the Insight's 120 NiMH cells, while using the stock inverter and motor.

His is a pretty cool project with far more KWh, but there's a junkyard a few hours from here selling a FEH pack, and I'm tempted.

 

It's been mentioned here numerous times that the FEH pack is 330V. The nominal not fully charged voltage is always used, nominal is 1.2V/cell and fully charged is around 1.4V/cell. Just like a very common RC Ni-MH pack that you can buy at Radio Shack is a 9.6V which has eight cells and I have four of them. A 7.2V pack has six cells. A "AA", "AAA", "C"", SubC(SC) or a "D" all have the same nominal 1.2V/cell, it's determined by the Ni-MH chemistry of the cell. You can do the math. Wikipedia isn't always correct that's why anyone can edit it!

 

Bill,

Evidently not always. http://www.hybridcars.com/gallery/22070/photo?page=2

Besides, 275 cells is an odd number of sticks of 5, which would place your output terminals at opposite ends of the pack.



So what am I looking at here, besides an enormous, inexpensive battery? I see the inverter on the right and ductwork at the rear of the car. Do the sticks run fore/aft or left/right, and how many cells tall is the pack?

 

This has been debated for a long time.
The FEH pack has "for sure" 250 cells. ( I've personally seen 'em all )

The resting voltage is very nearly 330v even when the computer reports 33% SOC.

There was talk about 5 years when they first came out that "enhanced" NiMH chemistry was used. After all, these cells are RATED for 100 amps (each!) which means they can exceed that amperage for very short periods.

I've seen hitting the brakes hard ( heavy regen ) put 400v into the pack (1.6v/cell).
You won't get a DTC until it exceeds 425 volts (1.7v/cell).

On the low end, 275 volts is the lowest I've ever seen under heavy load (65A) assist. (1.1v/cell).

The 330v rating is correct. 250 cells is correct.

 

I'm not an engineer but I think there is confusion here about the differences between amp-hours, amperes, and volts. On a more conceptual level, there are big differences between power demands and storage capacities of a 4000 pound FEH and an Insight that weighs about half as much and is much more aerodynamic.

 

A very strange way of stating the pack's voltage as compared to any Ni-MH pack used outside of the Hybrid world.

Because of this strangness, I doubt if you can use your method of stating V/cell based on max pack voltage since the pack is never charged all the way. How could you possibly get 1.6V/cell? It's just not possible with Ni-MH chemistry to get voltage that high because voltage actually drops just as a cell goes into a overcharge condition long before 1.6V/cell. The most perfered charging method is Negative Delta Voltage which looks for that voltage drop for the charge termination point.

 

I'm just saying it puts 1.6v across the cell when charging.
It does not maintain that.
The highest "resting" voltage I see is ~350v. (1.4v)

I virtually never see a "resting" voltage less than 330v.
And the car is not more than half charged by design.
More importantly, I rarely see less than 300v with the pack under load.
These are not your average off the shelf cells.

 

Using conventional methods of labeling, this pack should be refered to as a 300V not 330V.

From a '09 Ford WorkShop Manual:

High-Voltage Traction Battery (HVTB)
The High Voltage Traction Battery (HVTB) is a 216-397 volt DC source connected in a floating ground system. The battery receives, stores and delivers high-voltage electrical power when required. It contains the Battery Control Module - High Voltage Traction Battery (BCM-HVTB), which controls the higher functions of the battery. The BCM-HVTB also estimates the state of charge, estimates the power available and controls the battery temperature. The BCM-HVTB controls the battery temperature by activating or deactivating the fans contained within the HVTB, and by activating or deactivating the A/C system for the HVTB. For information about the hybrid climate control system, refer to Section 412-00B.



A Ni-MH "D" at 5.5Ah what was available at the time of pack's design. I think that they are Sanyo cells, maybe Twicells. As "D" cell's capacity has increased since the pack's design, it "may" be harder to find the lower capacity cells and they might have to be specially made. A pack rebuilder can do this with a large order.

Despite what is written, you can't leave brand new uncharged Ni-MH cells for long periods of time, they just don't come back to life when charged. I've had this happen, some leaked and some didn't revive even when cycled several times.