Short battery duration

Batteries, Chargers, and Battery Management Systems.
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nunchaku101
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Short battery duration

Post by nunchaku101 » Nov 30, 2017 9:41 pm

Hello

I have finally got my board going, I have a moutainboard with 2 X 6364 motors , Turnigy 200A Trackstar ESCs and 4X2s lipos 6000mah.

I can run my board around for a bit until the batteries are flat but I could not go from town to town. IS there a way to get longer battery duration? I have seen some people claiming to get 20kms on a charge and I like that.

Thanks.

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dogman dan
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Re: Short battery duration

Post by dogman dan » Dec 01, 2017 6:40 am

20 amp controllers or less.

6 ah x 65v is 390 watt hours.

if you pull max 200 amps, x2, that's 26000 watts. So to run an hour you'd need a 26000 wh battery.

Obviously you don't pull that much watts continuously, or even for one second.

Lets just say you might be actually cruising pulling 400w, that should get you one hour run time in theory, but more likely you have only about 300 watt hours you can really rely on from that battery. Do you get about 45 min run time now? ( flat, cruising, not hills or lots of starts and stops) That should be possible from what you have.

nunchaku101
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Re: Short battery duration

Post by nunchaku101 » Dec 01, 2017 3:31 pm

20 amp controllers or less? I do not follow.
Do you mean i should use ESCs only up to 20 amps?

The motors pull up to 65 amps I believe.
I get a bit confused my the maths part of it

I have ran it a couple of goes now, I don't think I get that much battery, when I have ridden it I have been riding it fast and not going at a constant speed. It just seems that after reading other peoples posts about their boards and bikes that most of them have something that they can travel with.

I am looking at these batteries but the cost is enormous. https://www.maxamps.com/lipo-16000-8s-2 ... ttery-pack

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Re: Short battery duration

Post by amberwolf » Dec 02, 2017 2:51 am

First question: how new are your batteries? If they're the ones from last year when you built the board and you've been using them a lot and hard, they are probably worn out.

Did they used to work as long as you need them to? But now don't? THen you just need to replace with new ones the same as what you had that worked.


Otherwise:

Before you start looking at batteries, you have to do the math.


How long, exactly, is your run time now?

To get a longer run time, you either have to increase the battery, or cut back the power usage.

Since you don't say anything about how long it actually lasts, we'll make up a scenario:

Let's say right now you ride for 6 minutes and the battery dies.

You said you need 60 minutes (1 hour).

So you need at least 10 times the amount of battery you have now.

If you have 6Ah of battery now, you need at least 60Ah of battery.

60Ah of battery is very large and heavy.

You don't specify what voltage you're running at, so I'll have to assume the 4x2s means you are running 8s, which is 33.6v fully charged, and would be about 30v average.

I'm running a 40Ah 14s battery, and it's heavy enough to just be able to lift it in and out of the trike.

Yours would be a bit more than half the voltage, so even if it was only 40Ah it'd still be very heavy (20lbs or more, at a guess). Needing to be 60Ah means it'd be 30lbs or more.


Now, since you have that much more weight and volume on there, not only is it more mass to accelerate, every time you stop and start it tkaes more power, every time you go up a hill it takes more power, it makes you less aero so the faster you go the more power it takes then, too.

So you'll probably actually need more than 60Ah, maybe 70 or 80Ah, to do 6x the range.


To figure out how mcuh more you *really* need, you'd have to specify your actual power usage in Wh/mile, *and* the actual range you really get out of it now, *and* the actual range you really need out of it, *and* the terrain you are (and will be) riding thru, *and* the speed you are riding at, *and* the weather conditions you ride in now and those you will ride in if they're different.


If you can't increase the battery, then you have to cut the power usage.

Current limit your controller. If you get 6 minutes and you need an hour, then you have to cut current usage by at least a factor of 10. So if you have 200A usage now, you have to limit it to 20A.

Faster you go, the more power it uses. So go a lot slower.

The more often you stop/start, the more power it uses. So don't stop and start as much (not usually possible).

The more hills (even slight slopes) you go up, the more power it uses. So plan differnet routes that don't have any slopes (not usually possible).

The more wind you have to ride against, the more power it uses. So make yourself more aero (wear tight-fitting spandex with no floppy or loose clothing), and ride in aero positions. (not usually possible). Even a little wind takes a lot more power to push against.

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dogman dan
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Re: Short battery duration

Post by dogman dan » Dec 02, 2017 8:23 am

No, if you have two 200 amps controllers, your motors DO, at least briefly, pull 400 amps from your battery. Motors don't limit shit, they pull all they can when loaded, till the rpm comes up and load drops, and then they pull less.

So the battery really hates that, I guarantee it. 65 amps each 3 feet later into your start up is plausible. But still a huge draw for such a small pack. Bear in mind, if hobby king says your battery can pull 100 amps, then pulling 40 on it is pushing it very very hard. Pull excessive amps, and the capacity of any battery will drop exponentially.

Yer beating your battery into dogshit dude. It needs to be much bigger to go the distance. Right now, I would expect 5 miles from it, not much more, based on how you ride. So about 8 km. You just cant pull much more than 40 amps from a hobby king pack that size, and expect anywhere near full capacity. If your pack is 20c type, then 40 amps is killing it.

20km from that size battery is quite plausible, at perhaps 20 kph, and few stops and starts or hills. That speed continuous would be no problem from your battery. Each motor would most likely be pulling less than 8 amps. ( assuming you don't weigh 150 kilos)

Its also possible you have your phases mixed up, which would make your motors hot as hell, and that heat would of course be lost capacity.

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Re: Short battery duration

Post by nunchaku101 » Dec 09, 2017 7:06 pm

Amber wolf, these batteries have hardly been used, they have not lost capacity at least judging by my charger.
The batteries I am using are Turnigy hardcase batteries which I think are around 25-35C.

Hmmm well if that is the case adding on that extra weight does not seem such a good idea. Perhaps I should use 2 sets of batteries or similar, I do like the idea of being able to go from town to town on it.
My voltage is 8s 30v.

So far my battery capacity has not dropped, if I ride it hard and get to 3.80V the capacity will drop temporarily for the next charge but go back to normal again when used and recharged.

The motor phases are fine, they do get a little warm but they have never gotten hot yet, same as the ESCs (though being winter that might help).

You said that 2XESCs mean 400 amp draw butt eh ESCs are run in parallel. Does that still apply?

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Re: Short battery duration

Post by amberwolf » Dec 10, 2017 1:02 am

nunchaku101 wrote:
Dec 09, 2017 7:06 pm
Hmmm well if that is the case adding on that extra weight does not seem such a good idea. Perhaps I should use 2 sets of batteries or similar, I do like the idea of being able to go from town to town on it.
Using 2 sets doubles the weight you have now, if the second set is identical to the first.

If you don't want to carry teh extra weight you'd have to leave a set of charged batteries wherever you expect to come near running out of power.

Or just carry your chargers (if they're lighter than the batteries) and stop somewhere to recharge before you'd run out of power.


You said that 2XESCs mean 400 amp draw butt eh ESCs are run in parallel. Does that still apply?
Amps add in parallel.

Volts add in series.

Watts add either way.

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dogman dan
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Re: Short battery duration

Post by dogman dan » Dec 10, 2017 7:24 am

To go town to town, triple, or quadruple your capacity. Obviously you might have to backpack a battery that big.

Never trust my math, somehow I got the idea you were running 16s.

8s means your battery is even smaller. 30 volts x 6 ah. that's a puny 180 watt hours. Nobody is going 20 km on 180 watt hours. Triple it to 540 wh and you might get where you want to go.

If you can fit it on the board, put 360 watt hours on it, then swap when you need to, for a second 360wh battery. Or go 360, that is, double what you have now, and get a fast charger.

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