Power Consumption for Dummies

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Post by scooterage » Mon, 02 Feb 2009, 23:04

its the original charger from the hefei gouxaun company..it has two lights..both red while charging then one turns green when charged full...the fan turns off when its full as well

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Post by Johny » Mon, 02 Feb 2009, 23:06

I followed the link and noticed that the battery is composed of 10 sets of 2 cells. At 3.2 volts nominal per cell I make that 32 volts. I would think that a true 36 volt pack would be 12 cells. The other notable specification is the maximum discharge current of 12 Amps. For a 10Ah pack that makes it 1.2C - very low.

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Post by scooterage » Mon, 02 Feb 2009, 23:11

oh...i'll have to check the cells inside im sure there were 12 tho...so the low (c) ? definately contributes to the low power (if the pack is 12 cells that is)
sorry still new at all this...

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Post by scooterage » Mon, 02 Feb 2009, 23:41

it does say that 10 cells...but what if its not 3.2 volts nominal per cell? i may be mistaken but it doesnt seem to say...it may be varied..the individual cells on sale there in the 10ah dont look the same as the ones in the case......but its a good spot to start
can i test the individual cells for the individual volts..what do i need to do that, and how do i do it?... i really want to learn more, but its hard with so much info but little q n a i have had acces to, to learn

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Post by fuzzy-hair-man » Tue, 03 Feb 2009, 00:03

scooterage wrote:...but what if its not 3.2 volts nominal per cell? i may be mistaken but it doesnt seem to say...it may be varied..the individual cells on sale there in the 10ah dont look the same as the ones in the case......but its a good spot to start
Cell voltage should be the same for each chemistry of batteries AFAIK so if they are LiFePO4 then they will have a nominal voltage of 3.2V per cell.

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Post by acmotor » Tue, 03 Feb 2009, 00:52

Just a thought...
Cells may be lithium polymer not lithium iron phosphate ?
LiPo are 3.6 to 3.7V nominal and 4.2V max charge
LiFePO4 are 3.2V nominal and same 4.2V max charge

If pack is max discharge of 12A then it is simply not suitable for an 800W scooter.
36V x 12 A = 432W maximum power you can draw. You need >800W ?
You would need 2 of these packs in parallel (but this may not be possible)

Note also the internal resistance is 100m ohm whereas the SLA batteries would have been less than half that resistance.
What is more, the 100m ohm may be per cell internally so the whole pack may have an ESR (equivalent series resisitance) of 10 x 100m ohm = 1 ohm so output would drop by 12V at 12A load. I would not rule this possibility out as the 1.2C rating is very low.

What this means is that the output voltage of the pack would drop by 1.2V with the 12A load compared with the SLAs voltage drop of less than half that.

Don't be put off by the lithium performance of this pack it seems not to be a good example given the load current you require.
800W / 36V = 22A (at least)
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Post by scooterage » Tue, 03 Feb 2009, 00:58

just checked the battery and it does actually have 12 cells...so it may not be the exact one they mention on that site, but it is same company... so being that it is 36v 10ah what would cause the reduced power compared to the 36v 12ah sla's...and being that it is for a e-skateboard, i would'nt have thought it would need the 10C current as its not a car or a high powered machinery that would need that sort of grunt, and i'm not that heavy so its not me..lol...with what ive read in forums and other sites on lithium batts it should easily push me up those hills much better than the sla's. what am i not seeing here?
can anyone help me out..


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Post by acmotor » Tue, 03 Feb 2009, 01:15

Ok 12 cells. >>>> LiFePO4

Even then the 36 volts is rather nominal.
12 x 3.2 = 38.4 and to charge fully would require 50.4V from the charger. (90% charge would occur by 45V though)

The SLAs would have been 36V nominal and (14.5 to 15V x 3) = 43.5 to 45V max voltage during charge.
Sorry, I didn't pick up what charger you were using.

Another way to look at things is the weight 3.5kg for the pack. Assuming 0.5kg for the box that leaves 3kg for (36V x 10Ah)= 360Wh. That is 120Wh/kg - sounds OK for lithium.

The bottom line is the discharge rate of 12A is rather low (1.2C).
Once again... just not designed for 800W load.
Many Lithium cells are rated at 3 to 5C at least (your SLAs would have been at least 3C rated). This would be more than enough for your application, but this pack seems to be targetted at the 200W ebike market ?

If you can find more info on the cells inside you could confirm this.
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Post by scooterage » Tue, 03 Feb 2009, 02:56

the charger manual is all in chinese, but i'll write down what is in english.
the charger is called a LCCL36V20E-T
other things wrtten that are legible are ..
220V+_10%AC, 50Hz (the plus minus is actually on top of each other)
<_120W
43.5VDC
1.8A
200+_10mA
5AH-20AH (i assume this means the charger can be used for batts between these numbers)
0-40c
4~6 (8ah) 5~7 (10AH) (i assume this is the charge times for this #AH batts

yeah it was from a 200w e-bike.. i just though it may have just meant that the discharge length of time would be less.
so am i probably best to just get the lithiums from the ev-power site? i cant find many sites that sell in oz and even if the batts are made overseas i dont like the idea of paying someone overseas and possibly not recieving them due to customs or just lost in mail...i feel safer buying from an oz seller, the lifebatt.com.au site does not seem to work, so the only real seller i have found is evpower. do you know of any others?....thats if there is definately nothing else i can do with this batt to better the boards performance



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Post by scooterage » Tue, 03 Feb 2009, 04:20

another question....putting cells in series and in parallel..in regards to making the volts and getting the right amps how does this work? can you explain this to me. particularly with the PHET cells.. rod at evpower said his runout 36v 10ah batt uses PHET..i think he said his normal 12v 12ah lifepo4 (sla size) batts use the same.
the size of the pack is 140wx140hx160l...i was hoping to resize the pack so it was 140wx70hx320l..it would then fit in the boards casing..

the e-bike lithium batt i already have has two fuses near the charge input and the ignition key...what are the fuses for?
sorry for all the questions i really appreciate your help!!

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Post by acmotor » Tue, 03 Feb 2009, 05:32

If charger is actually only 43.5V output then it will not fully charge 12 x LiFePO4 as noted in previous post.

Fuses limit fault currents. But not knowing your e-bike I can't say more.

I would talk to Rod at ev-power and Matt (antiscab on this forum).
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Post by antiscab » Tue, 03 Feb 2009, 08:01

oooo, i hear my name.

scooterage - quite a conudrum you have there.
that battery certainly isnt up to the task of powering an ev uphill. (even a ev scooter).
if the lost uphill performance is unacceptable, then your best bet would be to sell your current pack on ebay and buy another one.

on your original setup, at speed you draw 800w at 36v = 22A.
on 12AH SLA, you would be seeing 36v under load (maybe a bit less depending on how good the SLA batts were).
so you need a battery that will sustain 36v at 22A load to get the same performance as with the original battery.

a 36v 20AH ping battery off ebay might do it, though his packs are becoming quite pricey for what is offered.
36v 20AH ping battery

unfortunately, there is no cheap solution to getting the performance back reliably for your setup. there just isnt that much in the way of competition.
if you go for cheap cells, you will need a big pack (but will get lots of range).
if you go for small cells, you will need a smaller pack (but will have a shorter range).
SLA will last you as long as your first pack did.

the question i spose then is, how often do you use the scooter?
how much are you willing to pay?

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Post by Electrocycle » Tue, 03 Feb 2009, 14:51

I'd also expect the motor do draw well over 800w under high load conditions.
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Post by scooterage » Tue, 03 Feb 2009, 17:51

the ping batt is still at a 1c discharge rate, so wouldnt it still have the same prob of no uphill power, but just that it runs for a longer time then the 10ah that i already have (am i right about that?).... and it is sent from china...i really want somewhere in aus to buy (even if they import from china)..im looking at the evpower.com.au site these batts seem to be what i am after..the lifepo4 12v 12ah seem the best and at the right size as they fit the same casing as the sla's, but the runout one was cheaper at similar power (still at 3-5c) just a little less ah at 10ah ......the original specs of the e-skateboard are below if this helps at all.... i bought from lazyskate.com

Art.NO.: LW-014
Specification:
1) Battery capacity: 3 x 12Ah 36V
2) Motor power: 800W
3) Charging time: 3 - 6hrs
4) Speed: ≤32km/h
5) Range: ≤26km
6) Starter: wireless remote control-E
7) Battery input voltage: 90 - 250V
8) Max. load capacity: 150kg
Function:
1) Stepless speed change and ABS electronic brake
2) Automatically correct code and decode, controller is suitable to all
skateboard with same model and does not interfere each other
3) Automatically emergency brake offer safe anticollision protects
4) Automatically self-testing system troubles
5) Making alarm when wrong operation and insufficient battery happen,
automatically shut-off


its pretty damn fast on the sla's just that they dont last longer enough per charge...about 1hr depending on hills....i am after same power but longer run time...that also fit in the case if possible (3 12v slas side by side...approx 160x95x330 i think)(and the e-bike batt was a bit long for the casing so i had to fit the charge input/ignition part on the out side drilling holes thro the boards battery holding case {not the actually lifepo4 batts casing} and the batt fit on the inside, it looks really good tho.)
but thanks again for all your helping attitude guys...its really appreciated alot!!!!

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Post by coulomb » Tue, 03 Feb 2009, 18:06

scooterage wrote:another question....putting cells in series and in parallel..in regards to making the volts and getting the right amps how does this work? can you explain this to me.
I'll have a go at this one. First, let's consider series:

Image

The two parallel bars represent a cell; the long bar is conventionally the positive side.

Let's say each of these cells is a nominal 3.2 lithium cell. Think of voltage as a sort of "distance"; arranging the cells in a daisy chain like this gives us 3x3.2 = 9.6 volts "distance" between the positive end and the negative end of the series string. Unlike ordinary distance, though, the voltage has a polarity (think direction). If you connect two cells up positive to positive, the distances act in opposite directions, and the voltages subtract; you will get almost zero from that. If you reversed just one of the cells in the string above, two of the cells would cancel out (think going right 3.2v, then left 3.2v, then right 3.2 volts; overall, you get 3.2v right). Reversing cells like that for EV purposes is bad; we avoid this at all costs. It is possible (e.g. if you omit battery management) for a cell in a series string to reverse itself (so the terminal that is marked + actually has a negative potential with respect to the other terminal). This is very bad for the battery; charging it immediately (in the right direction) might save it from the worst effects, but it will never be the same again.

Now consider current. Think water in a pipe, but this water doesn't flow through air. Let's say there is one amp flowing through the first battery; there is nowhere else for the current to go, so each battery has 1A flowing through it, and the string as a whole provides one amp.

Now let's consider parallel:

Image

Notice how the "distances" are besides (parallel to) each other. The overall "distance" from the left to the right is the same as one cell: 3.2v. However, the 1A currents from each battery (let's just say it was arranged that way) end up combining at the junction point, so we see 3A through the paralleled cells. At the left, 3A is also coming in, and "splits" evenly into the three 1A paths to each cell.

Here, it's even more important to get the polarity right. If you connect one cell the wrong way around, a very large current will flow, causing a blinding flash, much heat (possibly a fire), and damage to the cells.

Now let's consider series and parallel:

Image

This is called a 3S2P arrangement: there are 3x2=6 cells connected with 3 in series, and two such series strings in parallel. For EV applications, they would probably be configured as 3 pairs of paralleled cells in series; the final voltages and currents are the same, but it's better to parallel single cells than series strings.

So now, we have three times the voltage, and twice the current capability of a single cell.

Supposing each cell was 40AH. The series string (first example) also has 40AH, but more energy than a single cell, in fact 40AH x 9.6v = 384WH.

The parallel string has 3x40AH = 120AH, but 120AH x 3.2v = 384WH.

The 3S2P arrangement has 80AH, but 80AH x 9.6v = 768WH. In fact, each cell, which has 40AH x 3.2v = 128WH, contributes 128WH to the total, as long as it is connected in some sensible way. So all sensible 6-cell configurations will have 6 x 128 = 768WH of energy. Energy can't be created or destroyed without a nuclear reaction (and even then it gets converted to/from mass).

So we can configure the right number of cells in series to get the voltage we want, and the right number of cells in parallel to get the current capability that we want.

I hope this helps some.

Edit: fixed some missing text.
Last edited by coulomb on Tue, 03 Feb 2009, 07:14, edited 1 time in total.

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Post by antiscab » Tue, 03 Feb 2009, 18:13

a batteries C rating is just a ratio of rated AH to max A.
so that 1C ping battery being twice the size of the one you have now is capable of twice the amps.
so you will get your hill climbing ability back.

the yesa batteries in my experience are very high quality (i use a couple on my scooter, and they show less sag than the TS cells of the same size).

the packaging of the pre-made 12v batteries rod cells i know less about.
i suspect you will need to balance at the 12v battery level, just as you should when running SLA.

do you have any details on your controller?
alot of small controllers are rated in battery side amps, rather than motor side amps.
so the controller just limits the power to 800w at low speed (thats how it was setup on my emax).
its also why bumping up the power is so easy.

if you dont have a controller, then electrocycle is right, that 800w motor will draw heaps more at low speed.
if you go with the yesa pack, your acceleration will likely be *much* faster than with the SLAs.

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Post by acmotor » Tue, 03 Feb 2009, 18:25

Well done coulomb, DC to daylight in one post ! Image
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Post by scooterage » Tue, 03 Feb 2009, 18:59

coloub ...so how is the parallel not cancellin out power as they are connected negative to negative in the begining or positive to positive at the end? this was my concern when setting a batt up that i didnt understand ...(sorry still learning alot)

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Post by scooterage » Tue, 03 Feb 2009, 19:03

is it cause that is wher the flow of the current begins and ends so it doesnt flow against each other but just splits at the junctions?

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Post by fuzzy-hair-man » Tue, 03 Feb 2009, 19:04

The ebay listing for the ping battery says:
Rated Discharging Amperage: 20 Amps
Max Continuous Discharging Amperage: 40 Amps
Maximum Discharging Current (Peak): 60 Amps
So that seems like it's rated discharge is 1C, it can continuously discharge at 2C, and has a maximum discharge of 3C.

60A x 36V = 2160W
40A x 36V = 1440W so you could hold it continuously at maximum and the batteries would cope, according to the specs anyway.

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Post by scooterage » Tue, 03 Feb 2009, 20:13

antiscab...it does have a speed controller, the guy from lazyskate only knows it is a 36volt controller..im not sure if that helps...the yesa pack? was that with the ping seller on ebay?...if so it is tempting being more amps for around the same price as the evpower 3x 36v 12ah batts
ping does make a flat type batt that is to the size of the skateboards casing

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Post by scooterage » Tue, 03 Feb 2009, 20:19

sorry i ment 3x12v 12ah

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Post by antiscab » Wed, 04 Feb 2009, 04:49

the yesa packs are the 12V ones that rod sells at www.evpower.com.au

the ping batteries are made by ping, and are much lower power (and thus much cheaper).

the 12V 12AH yesa packs are easier to work with, since they are a straight fit,
but the 36v 20AH ping battery will give more range for approx the same price (and i think he can make the pack dimensions to fit the same space as 3 x 12V SLA batts).
its all about compromises.
i must say Rod is very helpful, having bought my first LiFePO4 pack from him.

I havent yet done business with Ping, however over on the endlessphere forum, they seem to say good things.

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Post by coulomb » Wed, 04 Feb 2009, 05:49

scooterage wrote: coulomb ...so how is the parallel not cancellin out power as they are connected negative to negative in the begining or positive to positive at the end?
The difference is in a series string with negative connected to negative, you are measuring/using two positive leads, so the total voltage is zero.

With two batteries in parallel, yes you connect negative to negative, and also positive to positive, but you measure/use positive and negative terminals, which have the voltage of both cells between them (but not in such a way that they add).

So you could take two batteries in parallel, and break say the connection of the positives. Then you would actually have a series circuit, and there would be no voltage across the broken ends. However, each broken end is 3.2v positive with respect to the junction of the two negatives. Joining the two negatives together gives you the same 3.2v, but with twice the current capability.

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Post by scooterage » Wed, 04 Feb 2009, 14:46

anticab so the yesa have a higher max continuous current and peak? is that why they are more powerful? but being that i need min 22A continuous either should be the same in regards to the uphill climb (as the both pass 22A in continous current ) but the ping will go further distance. have i got that right?

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