Re: (ET) Time for a NiMH Elec-trak - Amp hours

["David Roden" <etpost drmm net>]

On 11 Apr 2005 at 12:26, Christopher Zach wrote:

> If one wants to charge faster, one needs to use either the saddle method 
> or a
> good temp sensor to detect fully charged. I think the Prius uses the 
> second
> method, and that's what I'm probably going to go with.

Never heard of a "saddle method."  can you explain?

While the Prius's battery processor does monitor battery temperature, I 
strongly doubt that it is the only or even the predominant method of 
determining SOC.  The controlling processor, like everything else in the 
car, is very sophisticated.  Besides, the battery in a Prius is not 
normally 
charged beyond 80% SOC, so I don't think that method would be usable.  
Most 
of the heat it does generate comes from its own internal resistance as 
it's 
cycled anyway.

The Prius pack comprises very high quality, closely matched modules and 
cells.  They are definitely not cheap Chinese sweatshop cells!  I think if 
you charge those packs you have until they get warm, you will ruin them in 
short order, and that would be a shame.

The temp rise method dates from the days of nicad batteries in laptops.  
It's unsophisticated and inaccurate and it depreciates the battery quickly 
- 
but it's cheap and easy to implement. There are better algorithms 
available 
now, for both nicad and NiMH.

A little advice on charging NiMH batteries has been posted right here.  
There's also quite a bit more of it to be found on the web and in 
textbooks. 
 Over the last few years, engineers have put a lot of time and effort into 
learning how to charge NiMH batteries for long life and good performance.  
IMO, you will be wasting the money you spent on the pack if you don't 
listen 
to them. 


David Roden - Akron, Ohio, USA

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