Power Consumption for Dummies

How do you store and manage your electricity?
scooterage
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Post by scooterage » Mon, 23 Feb 2009, 22:43

so electrocycle or lithbattboss could check the battery for overheating without the skateboard?...or check the speed control too...(tho i am not sure how it is going to be opened..but u guys seem to know what ur talking about...so i am sure u could work it out!!!

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Post by Johny » Mon, 23 Feb 2009, 22:44

OK so it appear to be the Lithium pack that is cutting out.
Based on the following:

1/ "Resting" the pack for a while after it has cut out gives you another 15 minutes of riding.

2/ Replacing the pack with the SLA pack immediately AFTER the Lithium pack has cut out allows the board to be ridden immediately.

So it's NOT the controller, it's the pack.

BUT

Why does it measure 39 volts when it has cut out? I have a feeling that this is a red herring. Can you measure the voltage on the pack AFTER it has cut out but while attempting to use power from the pack?
I think we have to assume that when the Lithium pack has cut out it still allows a small residual amount of current to flow and that is why you still measured voltage. It would be helpful to verify this.
i.e. No voltage after cutting out WITH load (you might have to run some light gauge temporary wires so you can try to ride it while measuring).

Except for the anomoly of voltage after cut-out, it sounds like a thermal issue in the pack. Most likely the BMS is monitoring heat in the pack.

It this point I would definitely email ping and get his take on this.

In the meantime perhaps you could investigate some form of ventilation for the pack. Is it in a sealed box? Can you ventilate it without too much problem with water ingress when raining?

So my advice.
1/ Email ping.
2/ Check about ventilating/cooling the pack.

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Post by scooterage » Mon, 23 Feb 2009, 23:32

ok sorry...it reads 39v before it cuts out...when it cuts out the multimeter drops to nothing straight away as if there is no connection at all..it doesnt reduce or slow down when or before power cuts out...it juts drops to 0 ..ok sorry about that.
i emailed ping 3-4 days ago..this is the longest he hasnt replayed to me..haha i think he may be tired of all my questions..it was $845 i wanted to make sure i did everything right ...the batt also got lost in transit that ping had to chase up..now i am asking so many questions he is probably tired...im suprised u guys havent given up!!
the pack is in the skateboards sealed box..it is slightly to big so i got a rubber matt with dimples like a masuer sandle...and lined the inside with it so it wouldnt move around....but it has air room due to the dimples but only small amount
i have been told not to use these boards when it rains as it is electric and can cut the power and damage the motor/battery control etc if water gets in...so i try not to use it whaen it rains


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Post by Johny » Mon, 23 Feb 2009, 23:47

Don't worry, we won't give up! The board is an EV isn't it? (Rhetorical question).
Good, then the facts make it clear. It make it 99% that the pack is overheating.
Best way to preserve the investment is to figure a way to cool the pack.
But you don't want to drill lots of holes in the box if it really doesn't end up helping.

There are obviously lots of possibilities here.
Anyone dive in...

First, figure a way to secure the pack inside the box without taking up air space. Air space alone won't help much but you will have to do this first so you can allow air to flow around the pack.

If you can find a small fan like is used on uProcessors and mount it at one end of the battery box with holes at the other that would be pretty good. If the fan voltage is a problem we can solve that but the higher voltage fan you can get, the better (up to 36V). Secure the pack using spacers that run the length - same direction as airflow and leave 20mm gaps between them. Strips of your rubber mat maybe.

If you don't want to use a fan yet, open up each end of the box as much as reasonable and do as above for spacers. It it helps but still cuts out maybe after a longer time then the fan might look attractive to you.

I can visualise a forced air ram-scoop on the underside of a skateboard... Initially made of stiff cardboard to check the effectiveness...
Last edited by Johny on Mon, 23 Feb 2009, 12:49, edited 1 time in total.

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Post by Electrocycle » Tue, 24 Feb 2009, 00:24

definitely sounds like the BMS in the pack is cutting power due to load and / or heat.

I can fairly easily set something up to test the pack out a bit more thoroughly.
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Post by lithbattboss » Tue, 24 Feb 2009, 01:31

I agree with Electrocycle. Definitely the BMS/controller if the voltage is suddenly dropping to zero. I hope the actual battery cells aren't getting hot or else you will have a second problem to address.

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Post by Richo » Tue, 24 Feb 2009, 02:07

So pull the pack out and bench test them.
Get a car main light (12V) or surplus spotlight for car.

Recharge the battery.
Leave for 30min to cool after charging.
Connect globe measure the current and voltage while the light is connect.
See how long it takes to cut out and what the voltage/current was at the time it cut out.
Try to do this at it's continuous C rating.
Ie if it a 10Ah pack at 2C then use 12Vx10Ahx2C= 240W globe.

Or find someone local to you who can do this for you.
So the short answer is NO but the long answer is YES.
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Post by scooterage » Tue, 24 Feb 2009, 03:03

ok...i know how to measure the voltage..but am unsure how to measure the current or amps as it is a 10a multimeter and the battery is 36v 20ah..sorry i am very much a beginner with the multi meter...how do i measure amps or current? how do i do it at its continuous c rating? if it is 1c at 20ah it makes it the same right? 240w globe..and why a 12v?

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Post by Electrocycle » Tue, 24 Feb 2009, 04:55

the best bet for a simple high current load is a bunch of nichrome wire from a heater element cut to the right length (for the necessary resistance) sitting in a container of water.

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Post by Richo » Tue, 24 Feb 2009, 06:08

Sorry I thought you had 3 x 12V lithium packs.
So if you have 1 x 36V pack then you need three 240W globes.
Or as suggested some nichrome wire - just don't burn yourself.

You 10A multimeter won't do.
So you maybe out of luck.

So the short answer is NO but the long answer is YES.
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Post by scooterage » Tue, 24 Feb 2009, 17:03

ok..im taking the board to elecrocycle to have the batt tested..thanks man!!
i resieved an email from ping...he said there is no temp control on the battery...he said to let the batt charge til it gets to 46v (as i charged it his recommended amount the first time for 10 hrs..i did 11hrs but it only got to 44.9v) so i left it to charge all day today(it doesnt overcharge so he said its ok to leave it on charge like that) he said that may be one reason it is cutting out, that the cells arent correctly balanced yet...the other theory with ping was that the board is drawing beyond the battery's peak (60a)when going up hill which can cause the bms to cut out the power. but i found the first time it cut out it i was riding on a flat road and not at full speed (i cant stay on full speed for long on the flat and definately down hill cause it is too fast and dangerous) and on the flat was when it cut out and not at full speed.... i thought it might have been an uphill problem at on time, but i tested it uphills (even quite steep ones) and it ran fine...within the 15mins of riding....i found it didnt matter what type of incline it was..it would cut out down hill even.
Last edited by scooterage on Tue, 24 Feb 2009, 07:53, edited 1 time in total.

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Post by scooterage » Wed, 25 Feb 2009, 15:19

this is the first lithium i bought for the board, that wouldnt power up the hills so well, but never cut out like the ping battrery is doing, is this because it has the internal resistance? is this what prevented that one from cutting out? as the max voltage discharge cut off and the max current is much lower....just a thought

Model 36V/10AH Sketch map of product
Nominal Voltage 36V
Average Capacity 10Ah
Internal Resistance ≤ 100m Ω
Discharge Cut-off 23V
Maximum Charge Voltage 42V
Maximum Charge Current 2A
Maximum Discharge Current 12A
Charge Method CC/CV
Assembled mode 2 groups in parallel connection and each group have 10 cells in series(though its actually 12 cells in series)

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Post by lithbattboss » Thu, 26 Feb 2009, 02:36

"Maximum Discharge Current 12A"
I think this says alot. There are some seriously steep hills around where you live in the Blue Mountains. Even with cells paralleled in pairs your are going to draw more current than 24amps from standstill/while accelerating up hills around your place. A Ping pack is just not designed for this kind of high discharge. It is more than likely the BMS is cutting off the pack to prevent damage due to excessive dischargre rates. It may just be able to cope without the BMS connected but then you are likely to kill the pack in a very short time.
Do you use your board on flat areas only or do you ride up hills?

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Post by scooterage » Thu, 26 Feb 2009, 05:08

ok ,with the board i use on flat and up some short hills not very steep...i ride the board mostly in the sydney city or around penrith,where it is used in the blue mountains is not very hilly, quite flatish area. The the thing with the 12ah lithium battery i have is that it slowed down alot up hill, but never cut out. the ping 20ah only slowed down a bit up hill, but would cut out on the flat as well as up hill, it had a higher max continuous and peak than the 12ah. so i was thinking there must be something different in the 12ah lithium pack,(i have three different batteries right now, 12ah sla, 12ah lithium, and 20ah lithium) to the 20ah lithium that is not causing the 12ah to cut out even quicker than the 20ah, something that just slows the power drawn when up hill and not cutting it out. so i brought this point up to maybe see if there was something added to the 12ah lithium to cause this difference compared to the 20ah. cause if the maximum discharge current is 12A on the 12ah lithium, why doesnt it cut out even quicker than the 20ah lithium. that is why i was wondering about internal resistance of 100oms on the 12ah. which the 20ah does not seem to have in the specifications, could this be the thing that is causing the 12ah not to cut out, but just slow down when more power is required for uphill?

(the 12ah lithium is a hefei gouxuan brand which does not cut out but slows down on hill
the 20ah lithium is a ping that cuts out)
Last edited by scooterage on Wed, 25 Feb 2009, 18:21, edited 1 time in total.

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Post by lithbattboss » Thu, 26 Feb 2009, 05:33

The 12Ah battery must have a higher discharge rate capability than the 20Ah Ping battery. Since the power cuts of suddenly with the Ping 20Ah battery it must be the BMS or controller which is cutting the battery off. Does this make sense?

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Post by antiscab » Thu, 26 Feb 2009, 07:57

since the battery isnt suffering sever sag, its the BMS.
just as with the BMS on my Yesa cells.

bypass the BMS and the problems go away.
Pings cells are good, the BMS boards arent. dont use these on discharge.
its the same with Yesa packs.

Ping batteries will do 3C.

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Post by antiscab » Thu, 26 Feb 2009, 08:02

lithbattboss wrote: The 12Ah battery must have a higher discharge rate capability than the 20Ah Ping battery. Since the power cuts of suddenly with the Ping 20Ah battery it must be the BMS or controller which is cutting the battery off. Does this make sense?


In the previous posts, the 12AH pack sagged much more than all the other packs.
the 12AH pack has a *much* lower discharge capability than the ping one.

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Post by scooterage » Thu, 26 Feb 2009, 14:09

both have the same discharge rate of 1C(with the bms).... so why didnt it cut out? if the 12ah lithium has a much lower discharge capability, wouldnt that mean it shouldve cut out alot earlier and easier than the 20ah? not just sag?. is this just the difference between the two bms on each pack, because that would make sense to me.
would it be possible to use the 12ah batterry's bms on the 20ah pack? or would that reduce the amps max discharge on the 20ah pack as low as the 12ah?
Last edited by scooterage on Thu, 26 Feb 2009, 03:40, edited 1 time in total.

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Post by antiscab » Thu, 26 Feb 2009, 18:20

the battery pack cuts out when the BMS decides the battery is being operated outside of its limits.
The BMS isnt necessarily all that reliable.

the discharge capability of a pack has more to do with how much voltage sag it can endure and how much heat rise it can endure.

unless you have dud cells, you dont need to use the BMS on discharge.
just make sure the BMS is still between the charger and the battery pack.

you could hook a buzzer up to the discharge side of the BMS to warn of single cell undervoltage, but this shouldnt be a problem since you are balancing on every charge.

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Post by Electrocycle » Thu, 26 Feb 2009, 19:03

had a look at it this morning.

The BMS appears to have basic balancing, and disconnects the charger when any cell is over about 3.9v
I think the undervoltage cutout is based on total pack voltage, but didn't have a good look at the circuit because it's all heatshrinked and we didn't want to open it up in case it needs warranty replacement.


So, my first step was to check the individual cell voltages at the balance connector.
There were two cells not giving any voltage at the connector pins, so I took the tape off and found that their balance wires were not connected.
One of those cells was at the same voltage as the rest, but one was down to 1.2v
After soldering the wires back on, the charge wouldn't start, so I manually charged the low cell up to about 2.5v, at which point the main charger started working.

Hopefully with a proper balancing charge it'll be ok!
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Post by Johny » Thu, 26 Feb 2009, 19:11

Wow - great work Electrocycle. That certainly sounds like the problem. It also boils down to a faulty pack. I'm amazed he got 15 minutes down the road each time. Could the wires have broken through rough handling (sorry scooterage)or do you think it came like that?
Either way, I'd be paying the shipping to get ping to change the pack. 1.2V is a tad low for the cell to be still healthy.

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Post by antiscab » Thu, 26 Feb 2009, 19:17

ive seen cells recover from 1.2v fairly well.
you could try the warranty route, but id find out if youve lost any capacity first.

but yes, well done Electrocycle

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Post by Electrocycle » Thu, 26 Feb 2009, 19:46

yeah first step is to see if it recovers, then if not maybe it's possible to swap out the one cell (actually three flat cells in parallel)

Looking at the wires I'd say it came like that, or at least broke in shipping.
The wires are not glued down at the point where they are soldered on, and some of them looked a bit weak.
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Post by scooterage » Fri, 27 Feb 2009, 04:30

well, i charged the battery for about 5hrs, the problem cell didnt get past 3.2 where as the others where 3.9 - 3.7 (the charge seems to cut out when one cells reaches 3.9v)
i took the board for another test, it went a bit faster to begin with than previously. tho the board cut out after about 15mins still. i walked it home and checked all the cells voltage as electrocycle showed me...all cells were 3.4v - 3.3v....except the problem one which was 2.8v.....
i am going to charge it again tonight and hopefully the cell will catch up to the other ones and discharge at the same rate. otherwise i will return the battery.
Last edited by scooterage on Thu, 26 Feb 2009, 17:34, edited 1 time in total.

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Post by Electrocycle » Fri, 27 Feb 2009, 04:54

yeah it sounds like the cell might have suffered a bit of damage.
It would probably help to separately charge it to 3.8v and then start from there, but if the cell's damaged it'll need replacement.
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