battery tools are crap

[Bill Wright]

It's just very convenient to be able to use any mains charger in the van. It doesn't matter about the inefficiency since the engine will be running.

Bill

[Johnny B Good]

====snip====

I'm not sure whether you're referring to the fact that pretty well all such IT kit utilises buck converters to provide the internal 5 and or 3.3 volt rails from their supplied wallwarts and as such can be powered off any DC voltage from 6 to 15 volts (or even as high as 25 volts in some cases) regardless of their nominated DC input voltage ratings in the 7.5 to 15 volt range, including 12 volts, on condition that the substitute PSU can supply the required volt amps, or whether you're simply stating that you use a 9v buck converter powered by the 12 volt supply to power your collection of 9 volt IT kit. Hopefully, it's the former rather than the latter interpretation. :-)

[John Rumm]

I get the impression he was thinking of the slightly more elaborate inverter style DC/DC converters, rather than the more common buck regulator which is only really capable of stepping down a voltage rather than say generating something that can charge a 18V battery from a 12V car supply.

[The Natural Philosopher]

the difference between buck and boost is almost semantic, with very similar curcuitry being able to do either.

Or in this case, the same.

[Chris Green]

Yes! :-)

I was using 'buck' rather loosely to include 'boost'. In reality they are very similar in implementation. If you look to buy one on eBay the only visible difference between a buck and a boost is usually the IC used.

I use buck converters on my boat to supply 9v and 5v devices and boost converters to provide the 19 or 20 volts required by most laptops.

What I was saying originally was that few cordless tool manufacturers seem to take advantage of the cheap boost converters to allow charging of (for example) 18 volt cordless tools from a car battery.

[Johnny B Good]

A buck/boost converter won't be quite as efficient as a buck or boost only type. The difference is only a matter of an extra one or two percent loss in the best efficiency buck/boost designs compared to the best efficiency versions of the buck or boost only types which, iirc, could be in the region of 97 to 98 percent efficient depending on voltage levels and power requirements.

Even way back in the late 70s, early 80s, there were boost converter chip drivers and powerFET devices that could raise a few hundred milliwatts' worth of 5 or 6 volt power from a single NiCad D cell replacement to a 4 or 5 AA cell NiCad battery pack at better than 90% efficiency. Although the 10% loss of battery energy more or less cancelled the 10 to 15% gained in substituting a full capacity D cell for a set of 4 full capacity AA cells, the big deal in this case was the elimination of the reverse charge syndrome inherent to any string of rechargeable NiCad cells made up with more than two cells in series.

At a stroke, you eliminate the inevitable chucking away of a bunch of still serviceable cells for the sake of the weakest in the bunch being destroyed by reverse charging. If you could use each cell independently of the state of the other 3 cells in a purchased pack, you'd be getting the full value out of each one in spite of a 10% variation in usable capacity between them that would otherwise accelerate the demise of a 4 cell battery made up of those cells (even if they had been precisely matched capacity-wise in the pack of four, it doesn't take too many charge/discharge cycles to upset the balance before the issue of reverse charging rears its very ugly head once more).

These days, the concept of "The Single Cell 'Battery'" has been resurrected in the form of the 3.7v Li-Ion 'batteries' as used in mobile phones (smart arsed or otherwise) and some P&S digital cameras.

Unfortunately, when it comes to allowing them to be totally discharged, unlike the case with NiCad and NiMH cells which can be left stored in this state indefinitely, this is a complete No no! Indeed, if you let a Li-ion cell drop below 2.4 to 2.9 volts the Lithium metal will plate out onto its internal structure, creating an unwanted discharge path as well as compromising the cell chemistry. However, rather than use a switching converter to generate higher voltage to power a 2 watt UHF transmitter in a mobile phone, the designers have simply used UHF power transistors optimised for lower voltage higher current working allowing an endpoint voltage of 3.5 or so to still permit 2 watts of transmit power to be raised.

I suspect that the only form of voltage stabilisation being used is of the buck converter persuasion since the laptop originated 3.3v alternative to the 5 volt standard of TTL is both below the 3.5 to 3.6 endpoint voltage of a Li-Ion cell and sufficient to allow the Tx circuit to produce the required watts to maintain the up-link path to the cell tower node. Since, contrary to all appearances (allowing a smart arse phone to become bogged down with energy sapping apps), battery life *is* still a prime consideration, hence the avoidance of the slightly less efficient buck/boost switching converter in mobile phones (I presume).

Boost converters to generate the tightly specified 18.0, 19.0, 19.5 or

20.0 volts typically used to charge modern day notebooks and tablets eliminates the extra conversion stage involved in running a mains inverter to power the original or replacement charging brick which simply has to supply a steady DC voltage to the charging port, leaving the notebook or tablet to manage the battery charging for itself.

Although Li-Ion battery chargers utilise switching converter technology to control the charging voltage and current, there's also a charge management controller included, tuned to the requirements of the battery pack or range of battery packs it was designed to charge. Li-Ion batteries are 'very picky eaters' of electric charge compared to pre- Lithium battery technologies.

Designing a charger for a single cell Li-Ion "battery" (3.6v) is pretty straight forward but once you have two or more cells corralled into a battery pack, things become more complicated, usually demanding the use of chargers matched to a particular two or three (or more) celled battery pack, largely, it has to be said, on account of the many inventive ways the battery manufacturer can choose to monitor individual cells or achieve charge balancing.

As others have mentioned, some battery tool manufacturers do offer such in-car chargers for a price. However, don't expect such chargers to be priced like a basic boost converter since they're a lot more sophisticated than that.

The point I was originally trying to make was that, with the obvious exception of 5 volt devices intended to be powered via a handy USB port or USB mains charger, pretty well all SoHo network kit intended to be powered from a wallwart designed to supply a DC voltage in the region of

7.5 to 15 volts, will quite happily work off a nominal 12 volt DC supply thanks to the use of buck switching voltage regulator technology to generate the stable 5 and 3.3 voltage levels typically required to power the logic chips used in such IT kit.

The lower limit on input voltage will typically be a little over the 5v mark[1] to give the buck switching converter a small margin to provide a stable 5v output whereas the upper limit is typically set by the voltage rating of the input filter capacitor, typically an electrolytic of either

16 or 25 volt rating.

I don't recall seeing 10v rated caps ever being used for the input filter but I suppose it's a remote possibility if the supplied wallwart output voltage is less than 10vdc regulated. Quite frankly, you're unlikely to see an input capacitor of less than 16 volt rating being used.

If you're entertaining the elimination of an 8 to 10v smpsu based wallwart in favour of powering such a piece of kit directly from a 12v battery supply, you can always pry open the casing (it's *always* plastic clip together casing on cheap commodity SoHo networking kit[2]), and take a peek at the capacitor's voltage marking to confirm your expectations (that it will almost certainly a 16 or possibly even a 25 volt part).

If, incredibly, it turns out to be a 10v rated cap, there's still the option of upgrading it to a 16 or 25 volt rated one if you're possessed of soldering skills, a soldering iron (a 25 to 35 watt Antex should suffice) and good old fashioned tin/lead multicore solder... oh, and a replacement cap! :-)

[1] Purely of academic interest in this case, but if the kit only uses the laptop based 3.3v standard for its internal logic, it may even still function perfectly fine off of a single 3.6 volt Li-Ion cell. [2] Eliminating an expensive metal case required to heatsink an analogue voltage regulator chip was *the* whole rationale behind the use of (at the time) the more expensive switching regulator technology option, along with being able to get away with a lower (cheaper) VA rated wallwart supply to boot.