Quote:
Originally Posted by Pizzazz
Another take on your data, I think it is totally acceptable to lose 1% capacity on every cycle if not charging to 100% during offshore passages. Once the passage is complete, the batteries can be equalized and restored to most of their original capacity. How many 30-day offshore passages away from marinas does the average sailor make in 2 years time? Not that many.
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That capacity loss was permanent and not recoverable. Equalizing is a too infrequently used Band-Aid for PSOC use and will only usually recover a 1-3% of capacity at best when done infrequently. Equalizing can be more beneficial if done more frequently but most boaters simply don't do this. By the time most boat owners get around to an EQ cycle, after extended PSOC use, the sulfation is hard, clustered and not recoverable thus the vast majority capacity degradation has become permanent.
We should also keep in mind that by industry standards a
battery is considered
failed when it can no longer deliver 80% of its original capacity. While batteries will still perform at capacities below
80% of new the risk of failure, such as an internal short, increases fairly steeply the lower we go. This is especially true in flooded batteries where weakened plates & grid structures can cause an unexpected failure. The highest rates of internal shorts/failures I see occur in flooded batteries but they can also occur
AGM or GEL.
Another often over looked aspect is Peukert effect. The Peukert corrected load on a larger bank of batteries, where average discharge loads remain the same as a smaller bank, serves to make the larger bank bigger in effective usable capacity rather than smaller.
300Ah Bank - Peukert 1.27 - 8A Load = Peukert Corrected Bank Capacity - Approx 355Ah - Peukert Corrected Load 6.75A
100Ah Bank - Peukert 1.27 - 8A Load = Peukert Corrected Bank Capacity - Approx 88Ah - Peukert Corrected Load 9A
The 50% recommendation is not one created by boaters it is one recommended by the
battery manufacturers themselves. In fact 50% is not really a suggested DOD. Most manufacturer's suggest the shallowest cycling possible results in the longest cycle life..
As one of the very few in the
marine industry who owns the
equipment to test actual battery Ah capacity, (at any given time I have two batteries under test, I have some Northstar's finishing up any time now) I can say that for
certain infrequent situations, with a quality battery bank, I do recommend 80% DOD. There is only one lead acid battery that is suggest 80% DOD as the regular discharge level and that is the Firefly Carbon Foam battery.
This recommendation is usually for short duration off-shore passages,
race boat passages etc., but I do not recommend that as a standard DOD for a PSOC use battery. Actually I can't say that entirely because I do have a few ultralight
race boats where the deign is for regular 80% DOD but they replace the expensive
AGM batteries yearly abd GEL batteries bi-yearly.. Even in just a yearly race circuit the AGM batteries are often delivering just 45-55% of original capacity by years end and are bordering on dangerous. GEL's do better but they tend to charge a bit slower. Prior to the Firefly the Odyssey or Northstar TPPL batteries were the usual choice due to speed..
If you were a day sailor who charged at a
dock after each sail, sure 80% DOD could give you a decent outcome
with quality batteries. The data I get to gather is based on actual real world testing of Ah capacity and being able to see and watch what different
use behaviors result in out in the real world. I suspect I have collected more of this
real world marine use capacity data than anyone else in the marine market.
A fair number of us in the marine industry have been talking about the misleading guidance presented in manufacturer cycle life data, with respect to
real world use, and finally the manufacturers are starting to openly discuss PSOC use.
The key word here is "discuss". On a sadder & more frustrating note we are now being
marketed PSOC use batteries with zero PSOC industry data, with the exception of Firefly, to back up the
marketing claims. Requests for PSOC testing data has been asked for repeatedly and as of yet only Firefly has been forthcoming.
On one "
PSOC marketed" battery it was found that it did no better in PSOC testing than one not marketed/sold for this use? Without manufacturer data how is one to know the truth behind PSOC
marketing claims?
Will we ever see PSOC testing data from the industry? I hope so, but if I had to guess I would say this is highly unlikely because 80% DOD in a PSOC
environment essentially murders
most lead acid batteries in very short order and no manufacturer wants to publish that type of a $hit show.
We do have batteries that handle PSOC and deep cycles better than others do and if you want to maximize DOD then the Firefly Carbon Foam or a quality GEL battery can perform quite well for this type of discharge level. I would not suggest anyone expect much from a run of the mill flooded "deep cycle" Group 24, 27 31 etc. at 80% DOD.
Data I have from East Penn shows a flooded "deep cycle" group 27 (DC27) delivering just 200
lab cycles to 80% DOD and this was under an
easy 25A reserve capacity test. The same case size battery from the same manufacturer, only in GEL, delivers 600
lab cycles to 80% DOD. While this cycle life number will be considerably lower in the real world, almost always less than half, it can still give a fairly respectable cycle number when compared to the flooded Group 27.