Author Topic: Batteries- Lead Calcium vs true deep cycle  (Read 67 times)

BruceM

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Batteries- Lead Calcium vs true deep cycle
« on: July 13, 2019, 04:56:21 PM »
My custom 120VDC battery charge management system was designed for 10- 12V AGM batteries in series, and has individual battery shunt regulators so that variations in batteries don't matter, and less equalization is needed.  I used cheap lead-calcium batteries (marine "deep cycle") initially for testing, and found that due to my very low average DOD, I was getting 4.5 years of service life. AGM batteries never came down in price so I've left well enough alone.  These Everstart (Johnson Controls) Marine batteries are stocked at the local Walmart.  They use so little water that I top them off annually, needing about a gallon of distilled water.  Low water use is one of the characteristics of lead-calcium.  They also have very low bulk taper charge characteristics similar to AGMs; as they become full, the charge current goes to well below 0.1 amps, typically below 0.050 amps.  This helps explain the lack of water use. 

I just added a T105 type (floor polisher battery - again "Everstart" by Johnson Controls though Walmart) 6V battery to my welder and am shocked at the difference in charge current.  The bulk charge current NEVER goes below about 2.2 amps, even if left on the charger, full, overnight.  I thought something must be wrong until I checked the Trojan data; they expect 2-3% of the C/20 to be the lower limit of charge current! 

I never fully technically appreciated the lead-calcium "Marine" batteries as I should have, since I was comparing them to AGMs and not wet lead true deep cycle batteries.  ( I use a 110AH AGM for my small 12V supply; I found 12 and 120V to be a very useful combination of home power). As long as you can keep your DOD below 20%, the lead-calcium seem to have good lifespan, good charge efficiency, very low water use.  They can also put out relatively high current, as I've found for the welder.   For my 120VDC system, currents are below 15A, usually well below that, which greatly improves effective capacity and efficiency.

It has been very educational to see how the T105 type 6V battery compares in a series application with the Marine (lead calcium) batteries.  While I have no doubt the T105 types will outlast them for the DC welder application, it gives me new appreciation for the Marine type batteries where DOD can be kept to modest levels for an expected service of 4-5 years.