As promised just before the New Year I’m going to begin an educational series here so that more people will have an understanding of some of the concerns and potential issues associated with what I will refer to as “new tech” batteries and the application of higher DC voltages in marine systems applications. As I off handedly mentioned in my pre-New Year post, this is good stuff, but it all must be handled very, very carefully to ensure on board safety.
So, let’s start out with some simple concerns related to higher capacity battery banks. I’m talking here about battery banks that look like the one shown here and larger:
Today’s two new terms are “short circuit current” and AIC, which is the acronym for “ampere interrupting capacity”.
When I see a battery bank like the one above I immediately think of how much electrical current could potentially be unleashed in the event of an electrical short circuit anywhere near this battery bank, for whatever reason.
Here’s what you the reader need to grasp here related to short-circuit current potential: A “shorted” lead acid battery has the capability of delivering anywhere from 100-1000 times the typical discharge current used in most electrical circuits on your boat.
Also, understand this, the effect is cumulative depending upon how many batteries are connected in a parallel configuration as shown above. There is some electrical resistance in the connections and wiring between each battery, but not much.
In the photo above you are looking at 5 Odyssey batteries paralleled. Now I can’t remember exactly which model Odyssey batteries they are as I took that photo about a year ago, but they look like they could be Odyssey model 31 M’s. If that is the case, and we’ll assume they are you are looking at what Odyssey will tell you is a potential 25000 amps of short circuit current available at the end of the string. You see Odyssey is one of the few battery companies that actually publishes this ever more important information in their specification tables. Hats off to them! We want more vendors doing the same! Check it out at www.odysseyfactory.com
So, term # 1 for today’s lesson: Short Circuit Current
Now let’s look at term # 2, AIC rating. This is a very obscure rating that implies how much electrical current a fuse or circuit breaker can be exposed to without literally welding the contacts in the case of a circuit breaker, or in the case of a fuse, turniong into a solid mass of metal. What does this mean to you the boater? The device won’t function as intended and stop the electrical current flow….. Are you starting to get the picture here? Do you want 25000 amps of electrical current running through your boat’s electrical system? Just say no to that thought, but understand that the AIC rating of fuses and circuit breakers, although an obscure value is really, really important, especially as we move to larger battery banks on our boats to meet all of our electrical load demands.
Tomorrow, I’ll talk about the effect of high DC voltage on AIC ratings so come back again.