Re: (ET) L/A charging

["David Roden" <etpost drmm net>]

On 5 Feb 2013 at 7:26, Robert wrote:

> Lead acid batteries can not be charged at thousands of amps!

Basic golf car batteries, of course not.  Nor is it something that most 
people do routinely.

However, batteries designed for high discharge currents, such as some AGM 
types, can generally accept charging currents about as high as their 
discharge currents, and at more or less comparable duty cycles.

I will say again that you cannot exceed 80% SOC at high currents, and it's 
also absolutely essential to monitor battery temperature.  Aggressive 
cooling is a really good idea.

A Solectria technician told me in 1999 that that Solectria Forces with 
Hawkers had been fast charged at over 800 amps at Arizona Public Service.  
They used Aerovironment chargers, IIRC. I didn't think to ask about the 
duty 
cycle or any special cooling provisions.

The cars in question had two parallel series strings of 26ah Hawkers, so 
each string was accepting about 15C (assuming the current balanced).  
Extrapolating to the largest Hawker battery of the time, 70ah, 15C would 
be 
nearly 1100 amps.  In theory, a golf-car-battery-sized AGM of similar 
design 
would be able to accept over 3000 amps!

Note that Hawker did NOT recommend this charging rate.  The highest fast 
charging rate I see in their datasheets from that time is 3.1C.  They 
reported elsewhere that "field testing has shown good operational battery 
life" at 5C, and that they had had positive results in lab tests at 9C.  

More Hawker information here 

http://www.evdl.org/docs/hawker-fastcharge.pdf

http://www.evdl.org/docs/hawker4e.pdf

To give you an idea of what can be done routinely and practically, Steve 
Clunn used to have a mowing business with a converted mower using 8 
Odyssey 
PC1500 batteries (62ah, 96v).  He had a dump charging setup in his truck 
that would charge the mower's batteries to 80% SOC in less than 10 
minutes.  
That's about 290 amps - roughly 4.5C.  

I guess my point is that big companies will often try to convince you that 
fast charging is something radical and new, and that their batteries 
(usually lithium) are the only ones capable of it.  It just isn't so.


David Roden - Akron, Ohio, USA

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