Just_Ed said:
I simply can't get it through my head why I need ,8,9 12, 16, 20 batteries.
if you want a certain number of ah, *and* a certain number of volts, you need a certain number of batteries to get that. you multiply the number you need to get the volts by the number you need to get the ah.
you can't count the ones already making volts to make ah, meaning you can't series ones already in paralle, and you can't parallel ones already in series.
if you need 48v, and your batteries are 12v, you need four of them in series.
if you need 80ah, and your batteries are 20ah, you need four in parallel.
so that's four times four equals sixteen batteries.
you can do that math for any voltage or ah batteries, for any voltage or ah pack made from them.
again, it's all about the wh.
do the math that way and it's easier.
you have 12v 20ah batteries; 12v x 20ah = 240wh. you need a 48v 80ah pack. 48v x 80ah = 3840wh. 3840wh total pack / 240wh per battery equals 16 batteries.
same thing with any other voltage or ah batteries, and any other size total pack.
I only have room for 4 SLA batteries period.
no...you have room for 4 *specific sized* sla batteries. what specific size batteries do you have room for four of?
meaning, what are the dimensions of the space you have available?
each different battery is a different physical size, as i showed in my previous post(s). i have a tiny sla battery here that is 6v and about 1ah. it's about half the size of a box of kitchen matches, maybe only a third, and it probably weighs a pound or two. i also have some group 35 slas out in the shed in a powerchair, and they're probably 25-30lbs each, and i'd guess around 8" x 6" x 7"? been a while so dont[' remmber for sure.
so you must define which specific battery you have room for four of....
I'm told that it's not the AH, that's important, but the WH.
Example if correct: 3 x 12v x 90ah = 3240 wh. I'm not seeing the relationship, between the 3240 wh and what the motors use. I'm sure I've read it, but it isn't seeking in the way its being presented.
So I'm still not connecting the wh, ah, between battery and motors.
everything matters for different reasons.
the wh is important for range, which determines how much pack capacity you need, and for calculating how many batteries of what size you need to get that total capacity.
the ah, or rather the c-rate, and thus the amps (a), are important for the controllers/motors, for how much torque you get out of them (and the voltage for what the speed is), not counting any gearing you put between them and the wheels.
(c-rate just means the capacity-rate, meaning how fast you can pull out, in amps (a), the capacity (ah) a battery has. a 1c 20ah battery means it can handle 20a all the time and still give you 20ah, and not overheat, get stressed, etc. a 0.05c 20a battery means it can only handle 1a and do that...draw 20a from it and it gets stressed and it wont' give the full capacity (like lead). a 5c 20ah battery (like mine) means you can pull 100a from it and it'll be just fine.
so if you see a c-rate, that's what it means. some, like lead-acid, have such a poor c-rate that they don't even talk about it the normal way, they instead call it a 20-hour rate, or the capacity you get if you discharge them over a 20 hour timespan. :lol: it's usualy pretty low. (if you had a 100ah sla, it's 20hr rate is 5a. kinda useless for our purposes). some are "high rate" so they use a 10 hour rate...so it's only half as crappy as the regular ones.
(you could get 10a out of them!). of course, they'll supply more than that current...but you don't get anywhere near the rated capacity if you use them that way.
I watch golf carts with just a single pack of 7 modules replace all those SLA batteries and off they go. Those golf carts are weighing in at +/- 800 pounds, without passengers.
My car weighs a measly 200 pounds at the moment. Maybe 500-600 gross (with passengers) when finished.
that's part of the point of some of my previous posts...the lithium, for it's size and weight, is much more powerful than the lead.
i have a "little" 2kwh+ lithium pack that's only about 35-40lbs, 52v40ah, 14s2p, dont' remmvber the dimenions but call it a stack of 7-8 good hardback books. maybe 10 if they're not all that thick, but arent' thin. it's 28 of the eig nmc "c020" cells, like jimbob01 is selling in the for sale section (but mine came to me old and used, unlike his). it gets my poor-aerodynamics trike that weighs 500lbs+ with me on it (600 with a good load in the back, more with one of the dogs instead) around 30 miles of range, in stop/start traffic, at 20mph, with full-throttle starts up to cruising speed, around 3500w or so for those few seconds, and around 800-1000w or so while at 20mph.
even my half-sized pack, just 14s1p, 52v20ah, will still run the trike normally...it just doesn't get as much range (about half).
if i had to do this with lead like i did way back on early crazybike2 versions, i'd have around a couple hundred pounds of it, filling the cargo area under the seat completely (instead of about a third of it), and overflowing into the dog/cargo area in back, and breaking stuff on the trike, and slowing my accleration down (or requiring bigger controllers to get the same accleration back).
so, yeah, not a fan of lead. it has it's uses, like the powerchair that needs the ballast anyway to keep it from tipping over....but i wouldn't want to have to use it on other bikes, trikes, or vehicles. not now that iv'e experienced better solutions.
since you don't plan on using the trike very often, like twice a year or whatever it was, the lead seems like a cheaper option...but you must keep ti charged all the time or it will be damaged or destroyed by the time you go to use it again. buying a whole new battery pack every time you want to use the vehicle is much more expensive.
i have a stack of spare eig cells like i use in my packs above, that have been sitting at the same storage charge for i guess it's been 2 or 3 years, on the battery bench, waiting for me to need them. they haven't changed voltage (or state of charge) in all that time. (i don't use a bms on any of the eig cell packs; haven't needed to...so theres' nothing to drain them except self-discharge, which they dont' appear to have much of).
but...the powerchair lead batteries died of self-discharge permanently within half a year of me parking it in the shed and disconnecting them (so the chair couldn't drain them), and then forgetting to go out and check and recharge it all the time. none of them take a charge anymore, and wont' even light up a car turn signal bulb.
so...out of pocket cost at time of purchase isn't the whole story.
I will just bungee cord them over the back .....Yea, that sounds like the thing to do.
).