I'm trying to figure out a good battery solution. I'd like to try to understand the power spec and real-world power usage of the electric starter.
It looks like the starter only pulls 50A max? I'm not sure though!:
The 2012 570 manual specifices a "E-START. ENGINE CPL. 0,45KW 08". Googling the starter model, I find statements of "OEM SM14 MITSUBA", and specifications for those to be 460W.
I assume that is at 12V nominal. 460W at 12A draws ~38.3A, and indicates a load impedance of of about 310 milliOhm. (Very roughly and naively calculated.) If we imagine that the absolute maximum voltage we'd get from the battery would be 15V, that could push up to ~48A through that load, which would be about 750W of power into the starter. (Surely the starter is specified in terms of electrical input power rather than mechanical output power?)
So I'm wondering if this could be correct?
Battery recommendations are usually given as upwards of 100A burst capacity (CCA). If the real-world current draw is only half that, I imagine that the tendency towards more burst current capacity is a quest towards less internal resistance -> less voltage drop under load (less "sag") -> the battery is better able to really deliver the rated starter power. But I may be mistaken.
I can't find more detailed specifications on the starter motor. It seems to be the same starter motor that the DR-Z400 has.
Any guesses or information?
It's very hard to find the exact battery ready-made which I think is best for these bikes: A123 M1B-spec 26650 cells, 4S1P configuration, with a protection circuit which protects against over/undervoltage, balances the cells, and still has enough maximum current capacity. EarthX is close, but their current smallest model is 4S2P and are therefore too big to fit in the DRZ airbox (and also too big for my wallet atm). I did contact EarthX and got a very good reply stating that they will indeed be releasing a 90mm * 50mm * 50mm battery in the coming months / quarters, which sounds like the perfect fit. And IMO 4S2P is actually a good idea and I might get one for the 570. But in the meantime ... it looks like batterspace.com has the right cells for sale for a good price, can spot weld the cells together (this is the part I hate doing myself), and they may have a suitable protection board as well ... with a 100A burst capacity. And that's why I'm looking to understand this
Incidentally I'm also quite interested the idea that Bushie mentioned in a thread here, to tap power to the starter itself from a protection board bypass, but to power the rest of the bike through the PCB, including the starter relay. I don't fully grasp the electrical topology to have a good feel for how exactly it would be done
It does make sense to me though.