Battery Questions / Input (speed, distance)

Here are some calculations i made. Would someone more knowledgeable than i review? Did i do this correct? The size motor does not effect distance? is this because you will get same distance but at different speeds? seems like a different motor couldbe less or more efficient, but i guess that is what the weighted section is for.

i used this formula for distance and the superblog esk8 calc for speed.

r spec @6s

r spec @8s

Sk3 @ 6s

Sk3 @8s

If these Calculations are correct i will be leaning to the 8s. Im just trying to narrow down some more parts so i can get things ordered.

I also Found these batteries. Im looking to run 4 of them. 2 in parallel and then in series to give me [email protected] they have a continuous 25C rating with a peak at 35C (10 secs)

If someone could give this the old once over. If i go to 8s i will need to get a new charger since the imaxb6 will not work. I checked the commonly used parts thread and there are not chargers listed. Any standby 8s chargers? in the meantime i will be on hobbyking. Thanks for any input and info.

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You Could still discharge in series and charge in parrallel.

The grey quote above looks familiar… hehehe.

Yep your calculations look correct. A good example of the better efficiency you get with higher voltage. 8Ah vs 10Ah and realistically the 1km difference will be negligible.

I too would discharge in series, but charge in parallel - so your charger should work fine. But you’ll need to at least disconnect to charge. Or go with BMS if you wan in-board charging. I don’t mind the extra step as it also lets me inspect my lipos and keep an eye on them when charging (vs in board). In pyrex container etc.

alright good info! Keep it coming. i don’t mind taking them out to charge as well. it is only one more step and i plan on putting them in an easily accessible container. also if something should happen while charging the whole board doesn’t wind up in flames. ;] will this take forever to charge them this way? it isn’t a huge deal as it will be for after work cruises, just trying to get my ducks in a row. not crap i have no battery let me charge at the office.

charging - that’s another whole can of worms. Or down the rabbit hole or something…

Your charging is going to depend on a couple key things.

1 - pack life vs quick charge. Your battery will have a charging “c” rating. Just like the discharge rating of the battery - it lets you know max charging amps.

2 - more complex setup with AC-DC PSU and you’ll need a Parallel balance board to utilize the need for more amps.

Let’s look at the specs for the Turnigy battery:

So 2 C max charge rate. 2x5Ah (5000mAh) = 10 Amps max charge rate! That’s quite a bit and will give you a fast charge. Like if you get home from work, want to charge and get out the door to ride before sunset!

BUT - nothing’s free. Higher amp charging and discharging decreases pack life. Usually decreasing the # or re-charges it will do before IR (internal resistance) or a cell will go (discharge before the rest) - which leads to puffing and all sorts of bad things (why i look at my packs before charging).

So to extend battery life, you usually want to do a lower C charge - like .25 C or .5 C - so on this turnigy 1.25A or 2.5A respectively. You can also charge just below “full” 4.2v per cell which extends life further - but decreases range.

Back onto chargers - if you have a b6acv2 charger (a budget charger i usually recommend) - it maxes at 5A charge rate - across all batteries you are charging. So 2 batteries would be getting 2.5A ea. That’s good for pack life, but going to be slow sometimes when you want to ride NOW!

A better charger like an iCharger (206/306 etc) can charge at 20-30A respectively (the first two numbers of the model is amps, the last number is # in series it supports). So the 206 could charge two of the Turnigy’s at 10A each for 20A total - FAST! or a slow .25 C charge for better battery life. A great option.

The downside of most chargers like this (iCharger or similar) is that they require DC voltage. So a separate AC-DC power supply is needed. You can get several really nice variable ones online, or do what i did and get a Dell Server (or other brand HP/Lenovo/etc.) power supply and modify (or buy already modified) to switch on and supply a huge 12v power source. I have two 750w in series for 1500w 24v to supply my iCharger 306b and Hobbypartz Thunder 1220.

A setup like this as an example of AC-DC PSU -> 8s Lipo charger:

And in order to need 20A+ you’ll need to connect enough batteries in parallel to utilize (also convenient and decreases swap and charge time) the full potential of a setup like this. The best ones i’ve found (will depend on which connector you utilize on your packs) is BuddyRC’s paraboard:

Nicer chargers typically also have a temp probe you can utilize. with an elastic band they sit against the pack while charging and will auto-shut down the charge if the temp of the pack spikes while charging. Heat almost always happens before a catastrophic failure on Lipo. So an inexpensive failsafe (usually a few bucks for the temp probe if not included).

Told you it’s a rabbit hole discussion and a ton of info to digest. Hope it’s not too long winded and makes sense. let me know any questions i can explain or help further.

GL!

that is quite alright, never too much info. Besides i am already in the rabbit hole just have to find my way out. i might research the modded psu solution as i build computers from time to time and have a few spares laying around. I appreciate all the info and will attempt to digest it all. :joy:

Alrighty then - more info for you to research:

Great forum thread w/ TONS of info: http://www.rcgroups.com/forums/showthread.php?t=1292514

Also can check out this guy’s tutorial/steps:

I was going to do this with some server power supplies from work… then found these on ebay for cheap already modified for 24v series. Did a quick search and don’t see that seller right now, but here’s a cheap dell PSU - i’d check on rcgroups if the modification steps are listed! If so, <$20 you have a 750w 62A 12v PSU!!!

be very cautious of series for 24v: http://www.rcgroups.com/forums/showthread.php?t=1799197 Some steps to help understand if you go this route.