there was a cordless 18v drill that got a good write up in Which so
went out and bought one - now I wonder if I did the right thing becaus it has a NI-CAD Battery ( not bad at 1.5 amp hours tho)
I know about the memory thing and have had drills in the past that hav not lasted long (small batteries) but I was wondering how the moder NI-CADs compare with the old type
Can anyone give me any advice/their experiences? shall I take it bac and buy a more expensive one or will it do for general use?
The problem is that it will be only be used for DIY stuff and so won be fully discharged ( and may be stored away 1/2 charged etc as it i used intermittantly)
It says in the manual that before first us it should be charged an discharged 5 times - sounds like a pratt on????
Ni-Cads are like cars. They come in all shapes sizes and quality. Generally, the ones supplied with cheap tools are cheap and nasty. Those with more expensive ones better.
Did Which test the battery for number of charge/discharge cycles? That's what differentiates a decent one from a poor one.
Doesn't matter. But *don't* discharge it fully. Recharge when the performance dictates this - don't be tempted to leave the drill running until it stops.
Sounds rubbish to me.
The other thing is the type and quality of the charger. That makes a vast difference to life as overcharging is about the worst thing you can do.
Could you elaborate on that please Dave? I recently bought a 'bargain' Bosch 9.6v driver and the charger seems very basic. Bosch tech services confirm that the charger only has a 'power' light & doesn't switch off when the battery is fully charged, and that the re charge time is 3-5 hours which has to be timed manually.
I've looked at buying a spare battery, but that exceeds the cost of the driver and isn't viable. I love the little Bosch machine for suitable jobs, but I'm completely confused about the charging thing.
Then make sure you only re-charge when the performance dictates this and observe the time religiously. If you want the best life from the batteries. Personally I prefer the old standard 1/10th capacity charge rate for 14 hours. Which is a convenient time between finishing work one day and starting the next. My charging bench has a one shot timer which does just this.
You could buy an intelligent charger - there are types available which do a wide range of voltages and capacities without needing heat sensors, etc. Mascot are my favourite. But unfortunately not cheap.
not lasted long (small batteries) but I was wondering how the
NI-CADs compare with the old type
Modern NiCd's are very good. The memory effect isn't such an issue these days. Obviously they don't hold as much of a charge as NiMh cells, but they are a lot cheaper and time proven.
discharged 5 times - sounds like a pratt on????
A new battery doesn't reach it's full capacity until it's been through a few charge / discharge cycles. Just normal use is fine.
The thing that damages batteries the most is over discharge. When you try to get "just one more hole" from a flat drill battery it drives the discharged cells in reverse and reduces their capacity.
Those are the worst type of charger since it's easy to forget the battery is on charge and the charge current is above the level where it can be left on charge indefinitely.
Even the most basic chargers like the Ryobi one hour type use a thermal switch in the pack to detect the end of charge when the batteries suddenly start getting warm. Proper charge detection uses negative delta V which monitors for a sudden voltage fall at the end of charge due to bubbles on the electrode surface.
A perfect battery that actually used a pressure switch internally to detect the pressure build up at the end of charge was developed by Uniross (I think). You simply couldn't overcharge those cells, but they were expensive and weren't promoted properly.
If you can handle a super long recharge time you could hack the charger by adding a higher value of series resistor to lower the current to something suitable for unattended charging.
There are several factors at play here. There is basic cell quality - some are just better made than others. The better ones will have lower internal resistances, and be able to supply higher peak currents. Better quality ones will also tend to perform more consistently across different examples of the same type of cell (see matching below).
Capacity varies greatly. Most batteries are assembled from SUB C sized cells. The lower capacity ones start at 1.3Ah, better ones hold mare.
Next you have matching - higher quality packs will have better matched cells (i.e. cells that exhibit similar discharge characteristics to their neighbours). This means that all the cells run out of puff at about the same time. This gives a nice sharp drop off in performance (rather than a lingering decay), and minimises the chance that the weaker cells will get reverse biased by the stronger ones should someone try to wring the last few drops of capacity out of the pack (this will kill cells PDQ!) If you want the highest quality packs then you need to use graded or matched cells (not usually found in power tools, but the performance electric modellers will go in for this sort of stuff).
The worst of both worlds in a way - enough charge current to cook the cells, and no mechanism for stopping automatically.
Treating it to a decent delta peak charger would improve it greatly. You can probably buy one of the ones designed for the blue Bosch tools, assuming the connector layout is the same or could be adapted, but it will probably cost more than the whole drill!
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are plenty of circuits about (and ICs that do all the cleaver stuff for you) so you can knock one up in you felt that way inclined.
Buy another drill then - cheap way to get a battery. Makro were knocking out 9.6V green Bosch drill drivers at £20 last time I looked.
Its built down to a price, on a relatively safe assumption that most causal owners will probably never get through more than a dozen charge cycles in a year. So even if the charger knackers the cells after only fifty cycles it will still feel like they lasted a good while.
Followed by a cheap charger that doesn't have any built in charge detection or time switch and uses charge current way above that which can be left connected indefinately.
A "one shot timer" is a very useful bit of kit for charging kit. I've made one from mechanical time switch. Simply move the motor feed to after the switch. Turn the dial to start it, set how long you want it to run and it does until the off point where upon it switches itself off.
From what I see the new NI-CADs are much better provided I do not ru the drill down to nothing (which I did with my old drill by wrappin the switch with string to zero it - and the batteries didnt last) an I just charge for the 1 hour it says
Possibly a timer would be a good idea - have one in the kitchen think!
So the overall impression is that I should keep the drill and not tak it back?
I bought into the Bosch 14.4V blue series and cells/chargers/tools seem fully interchangeable with the green series. Also the higher voltage chargers always support automatic charging of the lower voltage stuff as well.
The 9.6V Bosch series is probably near end of life - which is both good and bad - not worth expanding your collection of stuff - but bargains available on ebay (beware of lookalike batteries on ebay, that may be of questionable quality)
That seems to be a common pattern for the "pro" chargers (probably because the are proper constant current chargers and the voltage is controlled automatically in response to cell condition). My Makita 18V charger will happily do anything from 7.2V to 18V, NiCd or NiMH.
Just run it until it shows signs of getting close to empty - don't try to flatten the battery, or else you will kill it. If you have been using it hard and the battery feel warm, then let it cool off before charging it.
If it is a one hour charger - the yes
(chargers this fast normally have some form of automatic cut off, if it does then good. If not then be *very* careful not to overcharge as doing so with a fast charger will also nuke a battery quickly)
If it feels comfortable for you, and performs well enough (enough torque, run time, and the speed controller is ok), then keep it.
I used the very handy U6046/7 series of chips by Temic - originally designed for car heated rear window use and sadly no longer easily available. It's similar to a low power 555, but has a variety of input trigger facilities and the ability to drive a relay coil up to 300mA. Time can be from 3.7s to 20h by the selection of two components.
Well, the phrase 'deep discharge' springs to mind. It's a catchy enough phrase to imply to the less-knowledgeable[1] that it must be a Good Thing(tm) and something that everyone should have a go at.
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