batteries and the ah con

[averhamdave]

I don't have a BMS and lipo packs don't have them.
There are dangers but they are overplayed by people who have read all sorts of scare stories - but you do have to be careful. If I get on it I'll post a picture of a "puffed" 6s, 5000mah pack I have just pulled out of a battery.
As I said above though it has to be best to monitor lipos as you go abd only balance charge. Trouble with that is you'd be forever charging!

 

[Stalkingcat]

Trouble with that is you'd be forever charging

It sometimes feels like that but you can charge at 8amps just through the balance leads. Loads more if the balance leads are used just for the final low amp balance.

Would like to try one of these but can't quite bring myself to press the buy it now button.

What do you mean by lipo packs don't have bms's on them, you can put a bms on any pack.

They can be extremely dangerous. I've watched many a pack burn itself out cell by cell. Luckily I've been able to series disconnect them, so that only 5 or 6s goes up in one go. Id hate to think what an unattended 24s 20ah would be like. Smoke is the real problem, more of a smokey sparkler type thing rather than an explosion but could be if its contained without an adequate pressure release /smoke hole.

 

[jimmyhackers]

that icharger looks a bit of overkill. does it do 48V? the specification seem to suggest it doesnt.

ive had much success with my imax b6 chargers. shame they only go to 22v.

you could buy a few of them and "split" you battery for charging at a fraction of the cost.

 

[Stalkingcat]

Yes it will do 48v.
2x 6s lipos is around 48v you may run into problems with the LVC on your controller though?

You could split the pack (just one series connection) and plug each 6s pack into each channel, with everything still connected in parallel.
If you built a 20ah Lipo pack to replace your LA pack and tried to charge it with a imax b6, you really would be charging for ever at 50w max.

Compared to that, the 4010's 2800w is around 56 x faster, however the 4010 is prob not the charger to learn about it all on.
I'd start off with a B168 charger and a 30a switching power supply to run it. Less than £100.


If you want some cheap fun, stick with your sla's

If you want something plug and play and don't mind about twice the weight (compared to Lipo), get a purpose built Lifepo4. I started with a Ping pack but maybe better alternatives now?

If you want to skip the often expensive learning/upgrade curve, then the lightweight Lipo option is the way to go. Just do a bit of reading first.

If all that sounds like a mine field of info, let me know and ill try to explain specific points better?.....
..

 

[Kinninvie]

This is required reading for anyone wanting to use LiPo.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=52240
I charge my 12S Multistar lipos using a Meanwell NES 350-48 power supply as a bulk charger and as long as I dont go below 3.6V per cell they dont go out of balance.
As soon as I go below this they stray quite a bit and need a balance charge to get them back together.
I have a wattmeter wired into my batteries so I always know exactly how much energy I have used and how much is left.
I also carry a cellchecker and use it whenever I stop to double check things.
It only takes 15 seconds a battery to do.
http://www.ebay.co.uk/itm/331384608066?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

 

[Stalkingcat]

Just remember to unplug those little checker things after use, as they do drain the battery. I used them instead of a Bms when riding, forgot to unplug them once and had a none registering pack a few days later.

 

[Stalkingcat]

Also used to bulk charge with these below, set to start discharging once each cell reached 4.1v. Problem is that they get really hot; started charging with them in the fridge and the pack outside. Works but carrying a fridge around or asking friends to use theirs get a bit weary!
Battery medic

 

[Kinninvie]

I have a couple of those and they read different voltages and both are incorrect!
The individual voltages never add up to the same as the total either.
I used them a couple of times and first time the lcd went blue after 15 mins with the heat but it did return to normal when it cooled back down.
I then put them on a cold byre floor and that kept them cool ok but because of the differing readouts I no longer use them.
I prefer to do my discharging with the bikes and never charge until I am about to ride out.

 

[Stalkingcat]

I'm not too sure which ones read true?

A quick test of four different cell checkers on one cell.

Balance charger 4.19
Battery medic 4.19
Mini checker with alarm 4.17
mini checker no alarm 4.18

Different cell

Balance charger 4.2
Battery medic 4.18
Mini checker with alarm 4.21
mini checker no alarm 4.2

make of that as you will?

I'm thinking that the charger is prob the most accurate but it doesn't matter too much as long as the cells are all balanced on the same device.

 

[jimmyhackers]

thansk for the replies, i have those cell checkers already, good stuff. and lipos...tiny tiny lipos

ive never liked "fast charging" lipos. i have one friend who always fast charges his lipos (2c) and hes the only friend who ive heard multiple stories from of his batteries puffing and exploding.
4 imaxs would take about 4 hours to charge a 48v 20ah cell at a 0.25c charge rate. i always balance charge at about 0.5c and ive never had one go pop, ive had some for over 4 years and they're still working great.

im contemplating mocking up a "joke" 3300mah 48v lipo pack. all i need are some leads from my rc shop and i have a super light weight 2minute battery pack.

would be a nice insight into what drastic weight loss would do to the vehicle.
28kg battery down to about a kilo

just to check some maths here. if im running at 20 amps max.... that equates to 0.333r ah a minute. so its a theoretical 10 minutes at full blast from these batteries? probably closer to 4-5 as ill be running them at a high c rating, 6 to 7c

i know the best way to know would be to do it but....bare with me, i have some questions

currently with the SLA. when fully charged my 3 bar battery meter (when accelerating full throttle) dips to 2 bars. then when im closer to top speed it comes back up to 3 bars at full throttle.

releasing the throttle keeps it at 3 bars

when ive been on it for 30 minutes or so and i accelerate, it dips to 2 bars again but when reaching top speed it stays on two bars at full throttle.

releasing the throttle returns it back to 3 bars again.

even after an hour ive never got it to go below 2 bars and it always seems to return to 3 if i leave it for a minute or so. performance also seems unhindered. weird thing is if i get off and check each battery im getting about 12.2-12.4v a cell which is pretty much done in my book

first question, would a lipo have a less wavering voltage than the SLA's do?
meaning my meter wouldnt be jumping up and down under use and creep back up if left alone?

is my controller and the twist throttle meters supplied manufactured to work more so with the slightly lower voltages of lipo, life, lion batteries?

this would explain why the "low voltage" cutoff is so low on the controller (most ebike controllers). also why my meter seems to read batteries as full when they are not really.

thoughts, ideas?

thanks in advance

 

[trex]

the voltage that you measure varies a lot with the Amps being drawn.
It is not a reliable method to relate the voltage you see to the remaining charge of your battery. For a more reliable method, you need to use calibration - another word for guessing what would happen in between two known sets of measures, resting voltage and working voltage when the battery is full and when it's empty.

 

[Stalkingcat]

first question, would a lipo have a less wavering voltage than the SLA's do?
meaning my meter wouldnt be jumping up and down under use and creep back up if left alone?

Yes, its called 'battery sag' and Lipo has less of it than Lead Acid.

You will also notice slightly more acceleration with Lipo, as it means that when you accelerate, the pack doesn't sag as much, meaning more watts/power.

I wouldn't rely on your kit battery meter too much, or the controllers LVC as you are correct in saying that they are generally calibrated for use with different pack types. The controllers LVC gives some protection in the case of a catastrophic pack failure, however it relies on a reading across the whole pack. When using Lipo, each cell needs to be monitored, as it is possible for a cell to fail and the other healthy cells to discharge into it, which is where things get dangerous. The controllers LVC wont pick up on this as it will still be reading the packs total voltage which wont drop much to start with, by the time it cuts out, you bike will prob be on fire anyway.

This is why you either need some sort of BMS or a cell checker as previously described, with an alarm to warn you if any cells start dropping below a certain level.

You would prob be best to build your mini pack, forget about the throttle battery meter and install a cheap small Voltmeter directly to your pack (this way you will get an accurate reading of the whole pack).

A few of the cell checker alarms will warn you of any failure and will also sound the alarm one you start running out of juice.
You have to take into account the battery sag when setting the voltage that you want the alarms to go off. Otherwise each time you accelerate, your ear drums will take a beating.

 

[Deleted member 4366]

Your controller's LVC will be about 38.5v, which is a bit low for lipos. With only a 3.3ah pack, you can expect a lot of sag under full power. I would guess at least 2v.

You have to be aware that lipos have given up most of their charge by the time they've reached 3.6v per cell, which is about 44v for a 12S pack. After that they accelerate downwards rapidly. With such a small pack, that final drop to convert your pack to a paperweight can happen in less than a minute. Hopefully, your controller's LVC will save them, but don't count on it.

 

[Stalkingcat]

There maybe an issue with running multiple chargers at the same time?
Maybe you could give us the lowdown d8veh, as I cant use more than one of my chargers because of the shared ground, hence looking at multi channel chargers instead?

I'm not sure if this is the same for the OP's idea of running multiple imax b6's?

I have a few old PC power supplies but have yet to wire them up, been put in a cupboard along with many other sidetracked ideas.

 

[Deleted member 4366]

Very good point. You must disconnect the packs out of series to use more than one charger in case their grounds are tied, which they probably are.

I seem to remember somebody smoking something when he tried more than one charger. Was it Cwah?