L-16 "cycling" requirements? [RE-wrenches]

Fri May 20 11:44:36 PDT 2005

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I would also like to know where this idea came from that "batteries need
exercise to stay healthy"? Trojan discounts that notion. They have also
suggested that EQing a floating battery is unnecessary... the stir the
electrolyte myth doesn't wash.

As I understand it, batteries have two "clocks working toward their end of life.
Once clock is a chemical clock... that even floated with no cycling, they will
only last so long. The other is a cycle clock... that counts the number of
charge / discharge cycles. Also of consideration is the length of time they are
left discharged due to the resulting sulfation that happens to the plates.

We can talk all day about optimal bulk, float and EQ voltage settings, but
evidence suggests it is best to err on the side of slightly overcharging wet
cells rather than chronically undercharging.

I have found lead antimony wet cells are really not all that horrible in grid
intertied applications, especially as with modern inverters like the Outback,
float current losses are minimized. With hydrocaps watering is also minimized
and a "cheapo" like a Trojan L-16 will typically last a good 10 to 12 years...
similar to their life expectancy in an off grid system. Plus, they are very cost
effective. Yes, a better wet cell would be a lead calcium configuration but for
some reason (probably manufacturing quantities?) they are horribly expensive.

As I understand it, lead calcium's are best for shallow cycling and float
service. (Perfect for battery back up grid ties.) I suppose the reason for the
price differential is that they are not mass produced as lead antimony cells
are. Last year I did some research about the price to replace those lead calcium
wet cells at the hydro plant I work at since their "rated life" is nearly up.
(Guess who gets to take them home!)
I believe the cost is going to be around $9K for 12 kW.
10 kWh of AGM's are about $1.2K
By comparison 20 kW of L-16's were about $1.3K.

Price per kWh:
Wet cell lead antimony: $65.00; life span ~10 years = $6.50/kWh/year (deep
cycle)
Wet cell lead calcium: $750.00; life span ~20 years = $37.50/kWh/year (shallow
cycle)
AGM lead calcium: $120.00; life spam ~10 years = $12.00/kWh/year (shallow cycle)

If labor is included in the above numbers wet cell lead calciums are more price
competitive.

I agree that each application needs the proper battery configuration and
chemistry. Grid ties with battery backup optimally need a different battery
chemistry than off grid. The problem seems to find a cost effective approach to
this application.

So Doug what do you use? AGM's?

This is a pertinent topic for the list, as with Outback GFX inverters, grid
intertied systems with backup power with no longer have to pay the inefficiency
penalty we had with brand X's old SW design.

Todd

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