Re: Nigel Calder's video on parallel battery banks. He doesn't talk about the number of connections required for the various configurations (
neither does this print article). Some examples show what looks like a single cable running between the batteries. I haven't seen lug fittings that would do that. My experience is that there would be 20 crimped-on lugs and 20 connection points used in the buss bar system, which gets you "closest" to perfect
in theory. What are the chances of 20 fittings/connections all having the same resistance? I would think that a crimp/attachment point would likely be a larger factor than the resistance in a few extra inches of cable here and there. In the print article I cited, about the last paragraph states that for a two battery bank wired "fore and aft," there is no issue.
Here in lies the problem. Nobody, with all of their measurements and lab equipment have shown that I am going to significantly lower the life expectancy of my batteries by connecting them with whatever length cables work best for my boat. Yes, they make great measurements, and nifty looking graphs, but not one of them has shown any significant real world difference in my batteries that have what, a 5,000 cycle lifespan?
That's the same reasoning I'm using to eliminate a lead starter battery. Where are all the measurements and lab tests that show that I am going to significantly lower the life expectancy of my batteries by using a 4 battery bank of lithium to start my engine? How do we know if the only thing "new" about the new LFP combo/start batteries is the sticker on the side of the battery? I say this because I watched this happen to the Eco-Worthy 280Ah lithium. A year ago, the sticker on the battery said "Up to 15,000 cycles." Six months ago, the sticker said "
Up to 6,000 cycles." Now the
sticker doesn't say anything about cycles, but the specs that ship with the battery says "6,000 to 15,000 cycles" with no explanation. The spec sheet also state that peak discharge is 850 amps for 10 seconds. Time to put on a sticker that says combo/start battery?
I have found no real world testing, or even a plausible explanation, why 4 lithium batteries, each with a 250A continuous rating, can't be used to start a little diesel. Is that what drops the cycles from 15,000 to 6,000? That would still be about 6 times what a lead start battery can do. I'm beginning to see the wisdom of Will Prowse's recent statement to "
smoke 'em if you got 'em" (that's my interpretation). It made sense to worry and baby-sit lithium batteries when they cost 5 times lead-acid. Now, I'm just as likely to see Davy Jones before I wear out 4 lithium batteries.
Ksanders' bluetooth app seems more sophisticated than mine, allowing to look at more than one battery at once. My app references WiFi, but the owner's manual says that feature isn't available yet from Eco-Worthy. I probably bought a few months too soon.
I believe Barking Sands started his motor a couple of times with a 120Ah lithium. He also said he tried to read peak amp draw when starting, but I don't know it that was using the lithium or his lead. I know my draw is
somewhere around 500 amps, but I haven't sprung for a recording 1000A ammeter to get an accurate reading and probably won't. What I'm wondering about is the voltage sag and current draw differences between using a lead start battery and a lithium battery. Lead marine starting batteries are rated in Marine Cold Cranking amps. The allowable voltage sag is wild. A 750 MCC rating means that the battery can put out 750 amps for 30 seconds and stay above 7.2 volts. Most lithium have a BMS that would shut down at 10 volts, so they can't sag like lead even if they tried.
All of this got me wondering about just what is the amperage draw for my 4kw starter? I always assume that everybody knows more about Ohm's law than I do, so feel free to comment. Keep in mind that my last class on electronics was in 9th grade.
If, when I was looking at the 500 amp draw on my shunt when starting my 4 cyl diesel, the voltage sag on my old lead batteries could have been down to 8 volts (as deemed okay for MCC rating). That 500 amps would calculate out like this: (4,000W/8V=500A). If I changed to a four lithium bank for a starter, voltage sag might dip from 13V down to 12V (don't really know). 4,000W/12V=333A. From 500A to 333A, that's a 40% reduction just because a bank of lithium can't sag like lead. If the draw was 600A with lead, it could be 360A with lithium. That discharge is well within the "normal" parameters for discharge of 4 x 280Ah LFP. The four batteries combined have a 1,000 amp continuous discharge rating, so a kinda-sorta like having a 1000A MCC rated battery used to put out 360A. I just won't tell the batteries that the current is going to a starter.