Getting More Life from your Battery Bank
In larger battery banks, where you have multiple series - parallel strings of batteries, you run the risk of some batteries getting more “used” than others, and this degrades your pack performance. A simple way to reduce this effect is to cross-tie your batteries. This is a rarely used but important method of getting extreme life out of your expensive batteries. Here is an example:
cross-tied-battery-bank
The dotted lines are the cross tie cables. It’s also important to make sure your cables are heavy enough, that you are not losing power as heat through resistance. If you have caps on your batteries, not maintenance free, check the water levels once a month and top them off during charging. Do not overflow. Next we will discuss pulse desulfators as another method of extending the life of your batteries. Stay tuned.
Professionally, I'm an IT Engineer (Executive Level) and Electronics Tech. Philosophically, I'm a Green Conservative, and probably would have been a hippie in the 60's if I had been old enough. I live off grid, with Solar (PV), Wind, and veggie oil fueled diesel generator power, and have been teaching and living sustainable technology for over 10 years.
September 19th, 2008 at 8:59 am
Mick Abraham says:
Cross-tie cables per your recent article are one correct (also low cost/low
tech) step to leveling out battery voltages in a series/parallel pack.
Your original diagram shows more of the dotted line cross-ties than are
necessary. A 24 volt pack made up of eight 6 volt units would need only three
cross-ties, not six as you drew originally.
There are five “voltage nodes” in a 24 volt battery string built of 6 volt
monoblocs. Assuming two strings side by side as in your diagram, the “most
negative” nodes are already connected in parallel…ditto for the most
positive nodes.
Those “extreme end” parallel connections pose no hazards, because there is
essentially no voltage difference between the “zero volt node” on string one
and the “zero volt node” on string two. Ditto for the two “24 volt nodes”.
The practice of cross-tying the pack is sometimes called “massively parallel”
and that’s a good way to think about this. Just as the original parallel
straps present no dangers, additional parallel straps are intrinsically safe
when properly installed.
If a cable is connected from the 6 volt node on string one to the 6 volt node
on string two, there may be a small bit of energy movement through the cross
tie cable when first connected, but this will diminish as the tiny voltage
difference levels out.
It’s important to cross-tie only matching voltage nodes. Two strings (as in
your diagram) would resemble a railroad track…or a ladder. (If you rotate
the diagram 90 degrees from the original drawing, that’s easier to see.)
It’s also important that the original high amp cables be of proper gauge for
the power system design. Those cables will continue to carry the high current
for inverters, recharge energy, etc. The cross-ties are just there to maintain
a level voltage across each of the nodes.
I normally use #6 welding type cable when I build cross-ties. That’s probably
overkill but I’m all tooled up for quality fab in six gauge. I like to install
the cross-ties independent of the original high amp connections. Sometimes
that calls for a fastener trick or two…
Mick Abraham, Proprietor
http://www.abrahamsolar.com
Voice: 970-731-4675
October 27th, 2008 at 1:26 pm
I would like to request a battery diagram for more life from my batteries,useing 8-12 voltbatteries to a 24 volt inverter.
useing the cross tie method.?????????????