Bosch Uneo 10.8v external battery - anyone have a standard battery?

[biffa]

I have a drill body only Bosch Uneo 10.8v (or 11.1v using conventional terminology). I've made up a battery and connected it but when the trigger is squeezed the led lights and the battery voltage too low light flashes.  It makes me think that the 3 contacts on the front of the battery might actually be important - does anyone around Derbyshire have a battery I could put a multimeter across?

 

[Chocolate fireguard]

My understanding is that the 3rd terminal, the one that the drill doesn't use (or at least my drill doesn't use) is connected to the negative terminal of the battery via a thermistor and is used by the charger to regulate the temperature of the battery while charging. Important for Li-ion cells.
If that is the case then a "proper" battery will show about 11V between the +ve terminal and each of the others, while they will have nothing across them. A resistance measurement between these last 2 will show the resistance of the thermistor - a few 10s of ohms perhaps.

You imply that you don't have the charger that goes with the drill, so presumably you made up your battery from robust, non-exploding cells like Nicads and charged it in some sensible way.
I can't see why that shouldn't work.

On the other hand if you did try to charge it on the dedicated charger without presenting the 3rd terminal I can't imagine the charger working.

In my experience measuring the open-circuit voltage doesn't give a give a good indication of the state of charge or the health of a battery, unless it's absolutely flat or knackered.
Can you monitor the battery voltage while the trigger is squeezed?

 

[cavermark]

Don't have time to search just now but I vaguely remember a thread on here, possibly jarvist mentioned something about how they overcame the voltage cut out thing (could it also be over voltage?)

 

[biffa]

Mark - that was for the 7.2v version I believe. 11.6v is fine for a 3 cell LiPo battery

Choc Fireguard - Cheers for your help. I bought just the drill body since it was significantly cheaper and I am happy making up properly protected LiPo packs and prefer to have the drill a bit lighter for bolting.  On the 10.8v Uneo stuff there are two big +/- contacts and I can read which these are from photos of the battery packs.  However on front of the batteries there are 3 more contacts which is more than you need for just a thermistor (wondered whether the Bosch charge balances rather than the protection circuit in the battery, but that would leave exposed live contacts that would also need protecting)

You can see the battery with it's extra 3 contacts on the front here

I've had the multimeter across it as I squeeze the trigger and the battery voltage stays at 11.6v so it's not the battery's protection cutting out, seems more likely it's the drill getting its electronic knickers in a twist.

If no-one knows then I guess it's some peculiarity of this drill and I'll have to bite the bullet and buy a battery to measure.

 

[Rob]

I've got a couple of these batteries, both an original and an imitation. Will be in Sheffield tomorrow at the Sloans thingy, so i'll bring them along.

 

[biffa]

Cheers Rob, I'll bring a multi meter

 

[Chocolate fireguard]

When you find out please let us know - I need to catch up on some of this technology.
BTW, some internet sources do say that a proper LiPo charger monitors the voltage of each cell so it seems likely that's the purpose of 2 of the extra terminals. Perhaps there is a thermistor in there too?

 

[xKaroox]

Yes! Let us know! Do you think, that is possible to replace three 1.5Ah cells and use for example panasonic 18650 high current 2.9Ah? I have the the 14.4V Uneo with internal cells and i?ve make this replacement its great. I want to do this with a 10.8V version and take spare packs to bag.

 

[biffa]

I measured Rob's battery - looks like all 3 pins show a resistance to ground.  I don't have the piece of paper in front of me at the moment.

I found what I thought was the correct battery for ?13 on ebay which I bought planning to use it to fool the drill by removing the cells and connecting my cable to it.  It's the wrong battery but can probably be modified to fit.  Still on my to do list

ChocFireguard - Apologise if this is a bit basic! LiPo batteries above 3.7v must have multiple cells in them, and these cells will have slightly different capacities and will age differently.  When we charge the pack we want all cells to charge up to 4.2v (which is the safe voltage to charge LiPo  cells to).  If we measure the voltage at just the + and - wires I could measure 8.4v but have cells charged to 4.25v (over charged) and 4.15v (not fully charged).  To get round this we must either get the charger to measure the individual cell voltages and balance the voltage of the cells, typically you connect the +/- of the battery plus an extra balance charger connector, this often allows fast charging.  The other option is to get protection circuit module/battery management system that as well as protecting the batteries against over/under charging + short circuiting, also has a balance feature.  This means that you only need access to the +/- connections which can make the batteries a bit more robust.

 

[Chocolate fireguard]

Thanks for your reply biffa. It was very useful. It also gave me some phrases to use on Google and now I understand things a bit better.
There are some impressive energy density figures quoted for these cells, but it sounds as if a lot of care is needed in charging them. I shall try to squeeze a few more trips out of the Nicads I charge on my homemade charger for my caving light.