Originally Posted by sailinglegend
I've corrected you on this point in previous posts but you don't seem to accept that a small starter battery when parallel with a large service bank can be overcharged by over gassing. The starter battery may be fully charged in 20 minutes but a large service bank may be at absorption and gassing voltage for maybe 6 hours. On long motoring trips if the engine is stopped during a lunchbreak then the service bank will go back into the absorption and gassing stage for another 6 hours until the regulator cuts back to a float voltage. When banks are combined the starter battery may be accepting no charging current, but if it sits at its gassing voltage when fully charged it will gas more violently - not good for sealed batteries.
You can get the same problem when on shorepower when the microwave or air con switches on and the shorepower charger may just reset itself and the 6 hour absorption mode will be repeated
I repeat below one of my previous postings on the problems of too high a voltage for too long:
The current to the full second bank maybe zero, but it's the voltage that is doing the harm. This is basic, sorry advanced, battery chemistry which can be found via Google. In absorption mode all the batteries are going to be at the gassing voltage. (They like to gas a little bit). The second bank could be very expensive Bowthruster batteries not a cheap starter battery. Some clever battery combiner/followers, like Balmar DuoCharge, can have a boost voltage input of say 14.6 volts - well above battery gassing, but the output voltage to the second bank can be set to 14.1 volts which is below the gassing voltage. This setting can automatically be reduced further by a battery temperature sensor. Balmar's regulators are even more clever. For AGMs they set the Boost voltage to 14.38, hold that for a while and then reduce it below the gassing voltage to 14.18, for the duration of the absorption stage. They then drop to an even lower Float Voltage. Why do they do this? To stop the batteries gassing too much.
I've just quizzed Balmar on these gassing issues and had some very helpful feedback which confirms exactly what I have said above. They also gave me the following feedback:
"The ability to reduce the charging voltage to the standard flooded battery by half a volt has resulted in far fewer failures on the starting battery side as a result. I've heard that from the folks at Hinckley and Island Packet in regard to substantial reductions in warranty claims for starting batteries after they began to install Duo Charges instead of battery isolators in the early to mid 2000's." - BALMAR
I understand your Combiners do have, as you call it, a "Clever" voltage limit feature which you can turn on and limit the voltage transferred to 14.2. Not so clever because it doesn't LIMIT as you suggest, but appears to disconnect, so the second battery stops charging when 14.2 volts is reached. This means it will never charge properly. You say you do this to limit over-voltage on GEL batteries - which you also wrongly call AGM
I'm afraid your writings are fully of errors and bad engineering ideas.
Here is a real world example of an actual Yandina Combiner. Our boat, previously owned by my friends parents, spent 5 years on a 24/7 world cruise
(98% of the time on the hook). Because of engine driven refrigeration
and lack of wind
, cruisers do often have to motor
, the engine run time over that 5 years was 2800 hours!!
The owner, an EE, never converted to external regulation, did not believe in it. The alt was set for 14.4V. The only real modifications to the charging system were that the alt was fed direct to the house bank and the Yandina combiner was added. It also had a solar panel with a controller set for 14.4V. This means the start battery was combined for charging with a dumb regulator set at 14.4V for at least 2800 hours but when you add solar combining I can't even begin to guess but thousands and thousands more hours spent combined over that 5 years..
When we bought the boat the batteries were 6 years old. The start battery tested far better than the house bank (conductance testers). All that had been done is to keep the water topped up.
This represents approx 28 years of charging at "coastal cruiser" engine hours of approx 100 hours per year. We retired the house bank but the FLA start battery went on to start my brothers power boat
for another 4 years, 450 HP worth of outboards... I had no reason, at that point, after six straight years and thousands of hours of combined charging to get rid of it because it was still perfectly fine...
I have yet to see a single situation where an ACR/VSR caused an early demise of a start battery, especially one in warranty. I will have to talk with Rick or Dale about that comment.. I do find it rather interesting and contrary to what I see out here daily..
I even have boats where the Bulk 1 is set well above 14.6V. Of course I actually use expensive testers to confirm what I see or don't see. I simply do not see overcharging of start batteries by using either BOTH or a combiner and I have a large n=XXX to pull data from.. I also do not see it with Echo Chargers or Duo Chargers..
We can't forget that automobiles use the same battery technology we use and run around year after year after year for thousands and thousands of hours at 14.2V - 14.6V. Our two cars are set for 14.4V & 14.5V. My wifes car has 160k on the factory installed 2005 FLA battery. It is still going despite being "over charged" for 160K miles.
Theories are good but I work, test and measure batteries on actual boats and have yet to see a single case of overcharging that I can even begin to hint at being caused by a combiner.. In most instances the start batteries almost always outlive the house banks despite often being of cheaper construction.
Our recently retired start battery (7 years) was retired when we converted to LiFePO4
. It is still testing at better than new spec on Midtronics and Argus analyzers. Compared to new (actual baseline) it comes in at 96%. It was combined via solar for 7 years and a dumb regulated alt for 6 of the 7 years and then a smart reg pushed to 14.7V in absorption for the last year... The house bank is testing in the 92% - 93% range..
For 7 years I did little other than use my battery switch as an on/off switch and let a combiner do the rest batteries are about as perfect as one could expect including the start battery.....
By far the biggest concern we have on sail boats is chronic under charging. Over charging, in my experience, is very, very rare.
When I see it it is usually with an unregulated solar panel, failed battery charger, failed regulator or old single stage ferro
charger left on at absorption for months and months at a time and the electrolyte never checked..
I just recently worked on a 41 footer with installed Gel batteries and a combiner (optional equipment
package). It also had a properly set up voltage regulator for the gel batteries. Both the start gel and gel house bank are now 11 years old.... Pretty hard to blame the combiner for much of anything at 11 years old....
I have piles of cases I can point to with similar results. One customer who just did the great loop (power cat) with twin Volvo
diesels with dumb regulated alts and a Blue Sea ACR.. Don't know how many thousands of hours on those engines but it is a power boat
. Batts are still going strong....
BTW the Balmar Duo charger does NOT do float independent of the charge source, as you implied it does. It is a simple voltage follower with some programmable voltage parameters such as the "ON" voltage and the second banks voltage limit...