Jump Start Li Battery Pack.

[Paul Goff]

I recently bought a Suaoki 20AH emergency jump start unit, used it for the first time while camping at a festival this weekend and something odd happened.

It started at 100% charge on the LCD gauge, I used it to charge a mobile phone three times and that dropped the charge indicated to below 10%! I have yet to try to start a car with it.

My phone battery is about 3AH, it wasn't completely flat prior to each charge, or full after any of them, so I used perhaps 6AH of my 20AH.

Charged the pack today with the supplied charger which is rated at 1amp and it restored the pack to 100% in 6 hours, the instructions say 6.5hrs.

So the question is, does the battery pack charge indicator have a "suppressed zero" like an old fashioned car voltmeter, so that even when reading empty it is actually still at around 2/3 capacity and can therefore still start a car engine?
Or is the indicator deliberately toleranced so that it is ludicrously pessimistic.
Or have I been sucked into another purchase of cheap Chinese electronics with a super grotty battery in it?

Any one have one, or similar, and used it to start an engine from what appears to be a low charge level?

Thanks in advance.

 

[JohnArnoldBrown]

How does 1 Amp for 6.5 Hrs charge a 20AH battery?

 

[Nigel Hewitt]

I don't think they carry a huge amount of charge but they can deliver it in one big hit.
I have one. It's tiny and I admit I looked at it very suspiciously when I got it but it started a V8 Range Rover no worries.

 

[rorywquin]

I don't think they carry a huge amount of charge but they can deliver it in one big hit.
I have one. It's tiny and I admit I looked at it very suspiciously when I got it but it started a V8 Range Rover no worries.

20Ah is 20Ah no matter how fast or slow it is used - like a pint of beer.

 

[Paul Goff]

How does 1 Amp for 6.5 Hrs charge a 20AH battery?

It clearly can not, which was what my question was driving at
Either the actual capacity is about a quarter of the stated or the indicator is VERY pessimistic, intentionally or otherwise.

 

[rorywquin]

I recently bought a Suaoki 20AH emergency jump start unit, used it for the first time while camping at a festival this weekend and something odd happened.

It started at 100% charge on the LCD gauge, I used it to charge a mobile phone three times and that dropped the charge indicated to below 10%! I have yet to try to start a car with it.

My phone battery is about 3AH, it wasn't completely flat prior to each charge, or full after any of them, so I used perhaps 6AH of my 20AH.

Charged the pack today with the supplied charger which is rated at 1amp and it restored the pack to 100% in 6 hours, the instructions say 6.5hrs.

So the question is, does the battery pack charge indicator have a "suppressed zero" like an old fashioned car voltmeter, so that even when reading empty it is actually still at around 2/3 capacity and can therefore still start a car engine?
Or is the indicator deliberately toleranced so that it is ludicrously pessimistic.
Or have I been sucked into another purchase of cheap Chinese electronics with a super grotty battery in it?

Any one have one, or similar, and used it to start an engine from what appears to be a low charge level?

Thanks in advance.

What is the rating of the charger?

Maybe the voltage indicator is wrong.

My understanding is that Lithium type batteries to not survive well being left either fully charged or discharged.

 

[Paul Goff]

20Ah is 20Ah no matter how fast or slow it is used - like a pint of beer.

Not completely, the effective capacity varies according to a few factors, mainly discharge rate. Capacity is often quoted at the 20 hour discharge rate, which means that at 1amp discharge a 20AH battery will last 20 hours, but it will not last 1 hour at 20 amps, far less in fact. Conversely 1/2 amp discharge may well last longer than 40 hrs.
And typical starting current could easily half or worse the effective capacity!

 

[Paul Goff]

What is the rating of the charger?

Maybe the voltage indicator is wrong.

My understanding is that Lithium type batteries to not survive well being left either fully charged or discharged.

Quite, either the indicator is wrong or the battery capacity is about 1/3 of that stated!
The charger output is 1amp as I said in my original post, and 1 amp for 6hrs cannot recharge a full discharged 20AH battery.
My suspicion is that the indicator could be deliberately wrong to protect the bulk of the pack's capacity from being used by the likes of me charging mobiles etc, and then not being able to start their engine when push comes to shove ;-)

 

[Botus]

My understanding is that Lithium type batteries to not survive well being left either fully charged or discharged.

if you want a modern battery to last never discharge below 30% and try not to charge above 80%
fast charging damages batteries and should be avoided.... (electric cars and fast motorway top up is bad !!!!)
always charge your batteries regularly (min of every three months)
leaving your jump starter in the cold knocks it flat - colder it is, quicker it dies (check every 3 weeks in the really cold parts of winter)
your phone maintains contact with the enemy when switched off !!! so they can still locate you !!! and is why the battery on smart phones doesn't come out anymore!!! and also why old ones in the cupboard are all dead even if you attempt the 3 month top up recco above

 

[rorywquin]

Not completely, the effective capacity varies according to a few factors, mainly discharge rate. Capacity is often quoted at the 20 hour discharge rate, which means that at 1amp discharge a 20AH battery will last 20 hours, but it will not last 1 hour at 20 amps, far less in fact. Conversely 1/2 amp discharge may well last longer than 40 hrs.
And typical starting current could easily half or worse the effective capacity!

I've spent years abusing batteries in high power model aircraft, obsessively connecting watt meters, ammeters etc testing various propellor and gearbox setup.........and then monitoring flight times etc based on calculated figure.

20Ah is 20Ah no matter how you use it!

You can use it up in 10 minutes or over several hours depending on your application and there will be some inefficiencies but for the purpose of this conversation it is still like a pint of beer - you get a pint. - just depends how fast you drink it....

"Ah" is the measure of capacity........

 

[JohnArnoldBrown]

None of this makes any sense.
Not only can you not expect to charge a 20AH battery in 6.5Hrs @1A, you can't really expect to charge a 6AH battery in 6.5Hrs either, if it's a Lithium Ion, because of the constant current/constant voltage/topping off profile.
Charging your phone will not be 100% efficient, of course, depending on the terminal voltage of the Li Ion battery and the voltage step-down circuitry, so I can see three partial phone charges being enough to almost deplete the powerpack.
It depends, of course, what voltage the AH rating relates to. If youir powerpack had a giant single Li Ion cell at 3.7V 20AH, which was stepped up to 13.8V, say, then the resulting 13.8V would be the equivalent of around 5AH(if 100% efficient) if the USB charging port then used this stepped up voltage as the starting point for a 5V regulator, as it well might(cheaper than another, separate, step-up convertor?) then who knows?

I think you you should tear the thing down and investigate to further the sum of human knowledge.
Or send it to Big Clive.

 

[rf065]

I have one, it's been left in the car fully charged for a couple of months. I've checked it a couple of times and always says 100%, took it out one day to charge my phone and as soon as I connected it, it dropped to 85% charge. I suspect yours was never 100% since you last charged it, even although it said it was.

 

[S500 Pete]

I've spent years abusing batteries in high power model aircraft, obsessively connecting watt meters, ammeters etc testing various propellor and gearbox setup.........and then monitoring flight times etc based on calculated figure.

20Ah is 20Ah no matter how you use it!

You can use it up in 10 minutes or over several hours depending on your application and there will be some inefficiencies but for the purpose of this conversation it is still like a pint of beer - you get a pint. - just depends how fast you drink it....

"Ah" is the measure of capacity........

Ah is also the measure of how good the pint of beer is

 

[Paul Goff]

When I get an idle few hours I will have to get all skyentifik with my trusty multimeter on the lil orange devil in the hope of discovering whether the battery is not all that's claimed, or the little % meter is hopelessly pessimistic.
I'll be back ;-)

Thanks chaps.

 

[Paul Goff]

I have one, it's been left in the car fully charged for a couple of months. I've checked it a couple of times and always says 100%, took it out one day to charge my phone and as soon as I connected it, it dropped to 85% charge. I suspect yours was never 100% since you last charged it, even although it said it was.

Which is pretty much what happened to mine
It could just be simple case of the % indicator isn't able to tell the truth unless there is some load on the battery.

 

[Paul Goff]

None of this makes any sense.
Not only can you not expect to charge a 20AH battery in 6.5Hrs @1A, you can't really expect to charge a 6AH battery in 6.5Hrs either, if it's a Lithium Ion, because of the constant current/constant voltage/topping off profile.
Charging your phone will not be 100% efficient, of course, depending on the terminal voltage of the Li Ion battery and the voltage step-down circuitry, so I can see three partial phone charges being enough to almost deplete the powerpack.
It depends, of course, what voltage the AH rating relates to. If youir powerpack had a giant single Li Ion cell at 3.7V 20AH, which was stepped up to 13.8V, say, then the resulting 13.8V would be the equivalent of around 5AH(if 100% efficient) if the USB charging port then used this stepped up voltage as the starting point for a 5V regulator, as it well might(cheaper than another, separate, step-up convertor?) then who knows?

I think you you should tear the thing down and investigate to further the sum of human knowledge.
Or send it to Big Clive.

Absolutely John, it doesn't to me either, hence the post
All numbers are approximate guestimates too, I didn't time anything with a stop watch, or measure voltage and current.
I reckon that it was about 6hrs to full charge, and full charge was confirmed by me using the unscientific method of noting that the charger started cold, got warm, and then cooled down again as the charge load came down. And that the doodah said 100% again ;-)

 

[Paul Goff]

I've spent years abusing batteries in high power model aircraft, obsessively connecting watt meters, ammeters etc testing various propellor and gearbox setup.........and then monitoring flight times etc based on calculated figure.

20Ah is 20Ah no matter how you use it!

You can use it up in 10 minutes or over several hours depending on your application and there will be some inefficiencies but for the purpose of this conversation it is still like a pint of beer - you get a pint. - just depends how fast you drink it....

"Ah" is the measure of capacity........

batteryuniversity.com

 

[rorywquin]

batteryuniversity.com

Know it thanks.

 

[Paul Goff]

Update.

I have applied a few idle hours and my trusty Fluke multimeter to the task and have concluded that the little battery charge indicator is hopelessly pessimistic in terms of the actual state of charge of the battery, but probably deliberately so!
Started by fully charging the unit until the battery voltage leveled off at 12.78 the charger was cool and the indicator said 100%. Then let it sit for a while.

Started charging mobiles/tablets etc and took note of the display and the voltage shown on my Fluke. The discharge rate varied from 0.5 Amp up to 2.5A

As I would expect the voltage decayed fairly rapidly at first and then this slowed, and the voltage decay stayed slow for the next four and a half hours, which was how long it took for the charge indicator to show 8% (and I had run out of things to charge ;-) )
At this point the actual voltage was 10.80, well above the "flat" voltage of 10.2 for 3 lithium cells in series, and the rate of decay was still very slow.

Interestingly, the instructions state that no attempt should be made to start a vehicle if the indicator is below 30%, which corresponds to 11.1V at the battery, or the total nominal cell voltage (3 × 3.7V)

These jump start packs have a problem, 4 Li cells at full charge will be too high a voltage for modern car electronics, while 3 cells is possibly too low a voltage if the charge isn't pretty high!

Hence the little indicator is deliberately pessimistic AND the instructions are specific about how high the charge should be according to the indicator.

And also, as the indicator is just a suppressed zero voltmeter, it will not give a true reading even by it's own standards unless there is some small battery load. Consequently it is possible, at first glance, to believe that the battery is at full charge when it is not. This is almost certainly happened when I used it to charge my phone at the festival!

The reality is that even though it was reading empty ish, there was a good probability that it would have been able to start my car. The maker claims it will start a 4 litre diseasel, mine is much smaller ;-)

 

[alexanderfoti]

A few things.

You are not using the pack directly. You are using it through a 12v to 5v regulator which has inneficiencies, as does your phones internal charging circuit.

Assuming 100% efficiency for caulcations sake a 3AH phone charge will use approx 1AH of the 3S pack.

With inneficiencies etc its will probably be closer to 2AH.

Add to that, unless the pack is the size of your forearm, its probably closer to 8AH total capcaity, which starts to make a bit of sense.

I regularly use a 3S and 4S lipo pack to jump start cars. The 4s pack at 50% is approaching the running voltage of the car so is not too bad. If left plugged in, it will start to charge the lead acid pack as well.

I will post a picture up of the packs I use and their capacity, but most capacities listed for these jump start/portable packs are nearly made up.