how to charge battery externally

as above... as always...

i got two batteries for my sig3 and planning to get one more. i also have a lot of spare batteries for my MP900 (managed to get the last one at a cost of a nominal 5$ ) and for the jornadas, of course. not to mention the zaurus C760 (ok thats not a hpc ) and intermec 6651 and NEC 789... (out of my main hpcs, only sig2 and bsquare doesn't have a spare batt, getting one for sig2 later, and bsquare has it built in )

so the question is how i can ensure the spares are all fully charged and always. i do have an original NEC external battery charger for the 900 (ah, it was a very good deal), getting one for jornadas (because i got the dead j720 repaired... it was used as a charger until that ), another for zaurus... yes these chargers do exist, specifically made for them.

but what to do with the machines that don't have an external battery charger as an optional accessory?

my sig3 doesn't or at least i didn't find one... also i doubt intermec had such an option... (not sure about the MP789...)

and the fact i don't dare to leave my sig3 on AC for long just compounds the problem. (i don't like leaving the others on AC either, but sig3 is a special case, i'm really afraid it proves to be a problem once... long story about my sig3)

so how could i charge my batteries externally? i know it is possible somehow but do not know the details... how to do it? how complicated would this be?

thanks for any ideas

I want to do the same thing and I know I'm in for a fair bit of work to accomplish it. I have to get a hpc cabinet built first though.

It will be difficult for a few reasons. A lot of reasons, starting with the need for the correct transformers with the right voltages and current.

If you could fashion a clip to attach to the proper battery terminals on the battery pack you always run the risk of connecting the wrong polarity to the charger and frying something.

If you want to charge the batteries in the units get a timer and a power bar. Hook the power bar to the charger and the hpc adapters to the power bar.

Set the timer for 1/2 hour a day. That should be enough to top them up without cooking them

Edited by wallythacker 2006-03-25 9:14 PM

If you're dealing with Li-on or Li-pol batteries, there are such things as "Universal" Li-on battery chargers. I'm not sure how something like that would work with a 'smart' battery like a laptop battery, but they apparently work with simple 3-contact Li-on batteries pretty well. You have to set the voltages of course, but there aren't that many choices for Li-on batteries (They're all 3.6, 7.2, 10.8 or 14.4V from what I've seen - although they could be any multiple of 3.6V in theory). The hardest part is getting the "Universal" charger to fit your proprietary battery when no adapter plate exists.

I think Monica wants an " unattended charge every darn battery I have at once without me tinkering" approach. That's what I want too.

thanks for the answers

wally, what i need specifically is charge the batteries externally (refer to the title of the thread ). i don't want to put my units on AC just to charge the spare batts when i may want to use them (hpc's) at the moment.



i do have such a universal li-ion charger. where i got stuck is how i connect it to the terminals... only the jornada batts are simple 3-contact ones no problem with setting the voltage, it knows everything from 3.6 to 14.4V.

so, for example the sig3 battery has 6 contacts... what do i do...



yeah.. what's more the terminals on the battery aren't easily accessible, will need to work out some solution for that...
but first i need to find out how to connect them with the charger. the worst is that i lost the little manual for the charger. it has two ends, one black one red, not sure which is which


edit: only other solution i can think of is buying a dead hpc to use as a charger. lol. now that isn't easy with sig3 for example... and anyway i'd rather buy living hpc's... i know myself too well, i always revive the dead ones sooner or later lol.

Well, that's what I meant. You hook the external chargers to a power bar on a timer. That's the easy part. Those batteries should be always ready to go.

It's the batteries without external chargers that's the problem. If you want them all kept ready to go wouldn't you need a universal charger for each battery *unless* you remembered to switch batteries and settings for the universal charger each day? Or used dead hpcs as chargers?

mmm no problem with the external chargers specifically made for each hpc, i can keep track of the batteries.

my problem is how to use the universal charger... on a battery with 6 not easily accessible contacts... this doesn't look too easy.

can't somehow a battery charger be built for each model just like the real OEM battery chargers? could be built from the universal charger (heck i'll just buy a few more of those), somehow. ok, i don't have the expertise to build something like that... it'd be so nice though.

Well if you know what contacts to use on the battery pack and have the right voltage adapter you could rig up some spring clips to make contact.

After all, the charging smarts are in the battery so it's just a matter of making contact with the right terminals. I think you'll need to learn how to solder

How to charge battery externally – some technical hints

Well, Cmonex, here you have to gather information on several areas related to your batteries: pin-out for polarity and connection to the charger, voltage and current capacity of the battery, voltage and current capability of the charger, calculation of the charging current and time. Let’s take these points one by one:
Battery pin-out: this is usually marked on the battery, for J720 is as per the attached picture, unfortunatelly I cannot tell the significance of the two "-", I guess one is for the main charging current, the other one for sensing feed-back to the built-in smart charger. I cannot tell you anything for the 6-contacts battery, my engineering knowledge on Li-Ion batteries is limited. Anyway, it is important to note that Li-Ion batteries are not exactly like 2-pole general use batteries, they need special smart chargers to detect and control their charging needs. :-(

Connection to the charger: this is performed for J720 case through a connector plate (DDK Thailand)with 3 strips of metal of about 2.5mm width x 0.5mm thickness. ONE IS LONGER, which means will connect first, I guess for grounding purposes!!! I also guess that the charger built in the J720 is of „smart” type, i.e. it fully controls the charging current and time and is built specifically for the Li-Ion 3-pole batteries. Speaking of the 3-pole connector itself, you can search for it on the internet (depending if you know the brand = DDK for J720) or tinker one from 3 strips of metal hot-melt glued on a piece of plastic, yet this is not the most difficult point here.
Voltage and current capacity of the battery: this are also usually marked on the battery; for J720 the voltage is 7.2 V; capacity is 1.96 Ah (=Amperes * hours) for the standard battery HP F1281A and 4.5 Ah for the extended battery HP F1840A. The meaning of the capacity is how much current can you draw from a battery over a certain time period, e.g. from a fully charged 4.5 Ah F1840A you can draw in theory 0.5Amps for 9 hours. The calculation is theoretical and the time - current curves are non-linear (load dependant).
The User’s manual is stating that the battery „provides power to your HP Jornada for up to 9 hours of use. Optional Extended battery is available for up to 24 hours of use”. I am reading in these lines that for a minimal equipment configuration, settings and use of applications, the battery is able to supply an average current of 1.96Ah / 9 hours = 0.218A = 218mA for the standard battery and 4.5Ah / 24 hours = 0.188 A = 188mA.
On the charging side the manual says „the main battery takes approximately 3 - 3.5 hours. When the battery is fully charged, charging stops automatically; the battery will not overcharge if left connected to ac power.” So you can calculate the average charging current as 1.96Ah / 3 hours = 0.653A = 653mA. For the extended battery pack the manual says 5.5 to 6 hours charging time, which gives 4.5 Ah / 5.5h = 0.818A = 818mA.
Voltage and current capability of the charger: the open-circuit voltage must exceed the nominal voltage of the battery, in our J720 case 7.2volts. The current output capability must equal the rating printed on the HPC label, i.e. 2.5Amps, but this is only theoretical just to be on the safe side to cover both changing and J720 use. As shown above the charging current is much lower, 1Amp is more than enough. Please note that the charging current is dependant on the discharge status of the battery and decreases significantly from the beginning to the end of the process if no current control performed on the power supply. HP developed an external dedicated battery charger for J720 which is HP F1841A, you might find technical details on the internet for it.
Charging current and time calculation: here you have to take into consideration all the input data shown above from both the battery side as well as load side (HPC). As previosuly mentioned I know little about Li-Ion batteries, but I can mention some rules of thumb coming from the old times of NiCd batteries: for the loading current in order to extend the life time of the battery as much as possible it is recommended not to exceed 10% of the battery capacity, meaning for J720 standard battery about 0.2Amp. Hence to reach the full-loading status you need theoretically 10hours, but practically you need a correction factor of about 120 - 140%, leading to 12-14 hours charging time if you start from a complete empty battery. Reading this you might consider the charging time too long and this is why the manufacturers have shortened the charging time by pushing up the current to the detriment of the battery life time (theoretically).
Final comment: it is to highlite that the main factor for both the charging of the battery as well as its lifetime is the charging current. That is why it is important to observe it while choosing the charger unit. A standard mains adaptor does not fit exactly as output the nominal voltage of the battery specs (3.6, 7.2 or 14.4 V), therefore has to be selected with a higher value with caution on limiting / controlling the current by placing a series resistor between the charger and the battery. Example of resistor calculation: for a power supply set on 9 volt, J720 battery of 7.2 volt, average charging current of 0.2 amp the resistor value must be (9-7.2)/0.2 = 9 ohm with a dissipated power of (9-7.2)*0.2= 0.36W. The closest standardised value for the resitor is 10 ohm / 0.5W, leading to a current of 0.18A and a charging time of about 13 hours. At the end I want to underline again that I have no clue on how to connect the 3 pin battery to the charger, may be somebody else can help here. :-(

hi arlex,

thanks for your answer i'm sure someone can find this nice summary useful, so i'm glad you posted it. however i can't find too much of new information in there, especially as i want to charge a 6-contact battery (sigmarion III), not a jornada battery, i'm already ordering an external charger for the jornada. and what i need to know is how to connect the pins on the sig3 battery to the universal charger - doesn't seem too difficult to connect the jornada but no need for that as i'll have a HP charger for it. but i am confused with the sig3 battery this is my problem, the sig3 batteries

as for the charging current, a long time ago i was curious and measured 800 mA @ 12V when j720 was turned on and set at full brightness i used an ac adapter 500 mA @ 12V for months before i could get a better one and no problems. strangely it had no problems with charging the battery when the jornada was using full brightness, only if i wanted to use the modem as well, then it could no longer supply enough current...

li-ion is quite different in many respects from nickel based batts.. but i don't know if it is a problem for li-ions to charge them with more than 150-200 mA (or 10%). however it is an interesting observation, i've never thought of this

ooops...

What is needed is a large HPC cabinet, like wally mentioned. With something like 9 universal holding places and have charging adaptors for each HPC you have.

I think maybe the simplest way is to get dead HPC's, cut out the battery charging part to get the smart charger and the contacts and rebuild them into a cabinet (or just a small box). If you took the components to an electrical company I guess you could get them to rebuild the smart charger and contact parts.

Just a thought,

Nick

Nick, thanks, nice ideas

only problem, it is not easy to buy a dead sig3 or sig2.. (intermec is no problem i guess.. )

Yeah, that is the problem.

Nick