Vamo problem

[dave]

I've noticed a strange problem with one of my Vamo's. If it is left unused with a battery in it, the battery slowly discharges. It is only by 0.1 volts in about 5 hours, so would be easy to miss. I only discovered this because it was unused for several days and the battery had gone down below 2 volts! I monitored it after that with different batteries which is how I came up with the figure above. I haven't checked the other one I have yet, so I don't know if this is a general problem or if I just have a faulty unit. Anyone else noticed this?

[Mev]

wont all batteries discharge a little if left in a device ?

[DiscoDes]

There will be a small amount of power used, I guess you're not turning it off, just not using it?

[maccafan]

All devices with electronics have a small amount of idle consumption. The Zmax V2 idle consumption has been tested at 0.11 mA, the Vamo is 0.15 mA, the YJ LT 0.16 mA and the Provari 0.96 mA.

Better to remove the batteries if the unit is to be left untouched for extended lengths of time.

[blakey]

Dec 3, 2012 17:26:16 GMT maccafan said:

All devices with electronics have a small amount of idle consumption. The Zmax V2 idle consumption has been tested at 0.11 mA, the Vamo is 0.15 mA, the YJ LT 0.16 mA and the Provari 0.96 mA.

Better to remove the batteries if the unit is to be left untouched for extended lengths of time.

Yep, even the provari eats a little power when it's idle, switch it off and it'll last a bit longer or if it's going to sit around for a few days then macca is spot on - remove the battery

[alvoram]

Dec 3, 2012 17:26:16 GMT maccafan said:

All devices with electronics have a small amount of idle consumption. The Zmax V2 idle consumption has been tested at 0.11 mA, the Vamo is 0.15 mA, the YJ LT 0.16 mA and the Provari 0.96 mA.

Better to remove the batteries if the unit is to be left untouched for extended lengths of time.

so does that mean that over ten hours the vamo should consume 1.5mah of the batteries 2000mah(est?) Or around about that figure, because it sounds like it's using a lot more than that.

[dave]

It is indeed alvo. Of course batteries will drain eventually even if they are in nothing and at a slightly higher rate if they are, but I've never noticed a drop of 0.5 volts in one day! I've checked my other Vamo and over a morning it has not dropped by even .01 volts, so I guess there is a fault in the other one. I don't think I'm going to send it back to China though - I'll just have to remember to take the battery out when it is not in use

[alvoram]

So (disregarding the fact that battery capacities are rarely accurate, and there are other small factors in play such as such a small current draw as opposed to the 1amp that the capacity is apparently often tested at) if a battery was 1500mah, a battery would have to be in the vamo for 10'000 hours to go from fully charged to completely flat? Not bad really

This is interesting, you learn something new every day, unfortunately for me, I also forget 2 things, daily, that I'd previously learnt!!!

[maccafan]

The true capacity of a battery is in watts. The mAh means nothing.

You can get a 2000 mAh Li-Ion and a 2000 mAh NiMh. One has a capacity of 7400 milli-watt hour (mWh) and the other 2400 mWh.

The current consumed when idle is called quiescent current which in the case of a Vamo has been calculated at 0.15 mA. So the time it takes for the battery to go flat depends on the charge state of the battery. If you put a freshly charged battery in it will be consuming 4.2 x 0.15 = 0.63 mWh at the beginning and at 3 volts it will be draining the battery at 3 x 0.15=0.45 mWh. It's not a straight forward calculation and you need to calculate the area under the graph which can be done by knowing the slope of the decline.

But if you leave a unprotected battery like an IMR inside these devices for extended periods of time, it will undervolt causing irreparable damage to the battery due to the growth of dendrites within the cell which may lead to an internal short.

It may be the case that one of Dave's Vamo's has a leaky capacitor which is causing more than normal quiescent current to be drawn. I don't know if switching off the mod by pressing and holding the fire button for 10 seconds would prevent quiescent current from being drawn but I guess he could try that.

[alvoram]

Dec 4, 2012 17:25:18 GMT maccafan said:

The current consumed when idle is called quiescent current which in the case of a Vamo has been calculated at 0.15 mA. So the time it takes for the battery to go flat depends on the charge state of the battery. If you put a freshly charged battery in it will be consuming 4.2 x 0.15 = 0.63 mWh at the beginning and at 3 volts it will be draining the battery at 3 x 0.15=0.45 mWh. It's not a straight forward calculation and you need to calculate the area under the graph which can be done by knowing the slope of the decline.

So you would still get over 10'000 hours out of a fully charged 2000mah battery on idle?

Without knowing the slope, and taking into consideration the decline in consumption as the voltage drops 7400 mWh / 0.63 = 11'746 hours, And that figure would be higher if you calculated the decline in consumption too. Is that right?

If it is I'm still surprised by this, I thought they would discharge on their own faster then that, never mind in a mod.

[maccafan]

Li-Ion batteries have a very low self discharge rate..

Once it goes below the safe voltage of 2.75 volts the battery will self discharge at a very high rate due to undervolting so no it won't last 10,000 hours or whatever.

[vapee]

I read the vamo v1 had a problem with the battery housing not being insulated, maybe that could have something to do with this.
Also they reccomend keeping the li-ion batteries at 3.7v when storing them for a while, but not sure how long is safe for it not to discharge completely. I think you can charge one fully and leave it for a few weeks or month though, but its good to use them every now and then.

They had some problems with the battery spring not being long enough for some batteries and maybe too short for other protected ones, but the v2 I think took care of that mostly.

[maccafan]

The V1 had an issue with flattop batteries shorting.

In the V2 they added a insulating washer around where a flat top would sit to solve the issue. I think they also added a slightly longer spring as the full body was really made for 2 x 18350..

Yes it is apparently better to store Li-Ion batteries at 40-50% charge for long term storage and also to not charge them to 4.2 volts but to 4.1-4.15 volts. Prolongs the battery life significantly in terms of cycles. I really don't understand why chargers don't stop charging at 4.15 volts..

[alvoram]

Dec 4, 2012 18:01:13 GMT maccafan said:

Li-Ion batteries have a very low self discharge rate..

Once it goes below the safe voltage of 2.75 volts the battery will self discharge at a very high rate due to undervolting so no it won't last 10,000 hours or whatever.

But are they not measured and rated to take into consideration that they shouldn't be used below 2.75? If not then that is a bit misleading IMO.

[maccafan]

Dec 4, 2012 23:14:09 GMT alvoram said:

But are they not measured and rated to take into consideration that they shouldn't be used below 2.75? If not then that is a bit misleading IMO.

Yes..I did not explain that very well..

But once they go below 3.2-3.3 volts they hardly give out any energy and plummet to 2.75 volts..This energy discharge graph at 0.2 amps (200 mA) shows how they start dipping at the beginning and the end.



What I am trying to get through is you cannot take a battery capacity or voltage and work out the time it is going to last for a given load the way you are doing it by simple multiplication and division. The energy it gives out is not proportional through it's discharge curve at safe voltages. At 4.2 volts the plummet is quite quick and then it stabilizes at around 4.0 volts and then again starts to plummet at around 3.3 volts and then undervolt if it is not protected.

The capacity is calculated from 4.2 to 2.75 but the battery becomes almost unusable ie., flat below 3.3 volts..Any load and the voltage will just plummet without much energy being given out..