New Way to Trickle Charge!

Hello,

This is a long story

It started when i bought a new cordless drill back about 6 months
ago. It came with two battery packs, which was nice, for only
$30 US at Home Depot. It's a 9.6v model drill. The drill came
with a 'battery charger' that also doubles as a radio OK, i
know that sounds strange, but the charger is actually a radio
with battery charging capabilities. The radio doesnt work very
well however, for pulling in faint signals, but the charger does
charge. I had hoped it was a 'smart' charger, but it wasnt.

The problem is, the charger keeps about 100ma (maybe a little
less sometimes) pumping into the battery pack, so leaving the pack
to charge 24/7, 365 days a year, will shorten the packs life down
to maybe a year or two. I didnt want to leave the pack out of
the charger either, because then you forget about it until the
next time you go to use the drill, when you find it's depleted too
far to use for anything practical, so you have to wait for a pack
to charge up before you can use the drill.

OK, so now you know the problem The question is, what is the
best way to do something about this?

I could open the 'radio/charger' and tinker with the charge circuit
to set up a trickle charge, and mount a switch on the thing to
switch between 'full charging' and 'trickle charging' which isnt
such a bad idea. On the other hand, it will void the warranty.

OK, so another idea would be to build up a new charging circuit
just for trickle charging, which wouldnt be too hard to do.
On the other hand, it will pretty much void out the original
charger and i'd have to have still yet another charger laying
around, and plugged in constantly.

Then i remembered some advice i had given on perhaps this site or
maybe another site, about using a timer to turn the charger on
once per day for about 15 minutes or so. At about 100ma, that would
ensure the correct trickle charge to the battery pack since
it would only be running for 15 minutes a day.

Well, the other day i was at Home Depot again for some other things,
and i noticed a small timer for $5 hanging on one of those displays.
It had four 'tabs' for turning something on and off up to twice per day.
Needless to say, I bought one and brought it home.

I plugged in the charger and pack, and set it up to turn on twice
per day (for now) but the intervals are set up such that you cant
turn it off before a 30 minute period is up. The way i figure it
though, 30 mins a day probably isnt too bad either so that's what
im going to do from now on. The charger will turn on once per day
and run for 30 mins and turn off again, every single day.

So far ive been monitoring the battery voltage and i'll probably check
it once a week until i determine that this method works good enough
to replace conventional trickle charging. I think it will, and i dont
think that the slightly more charge time will hurt the battery pack
either.

I just wanted other people to know about this technique so they can
keep their drill (or other portable tool) battery pack charged up
without worrying about damaging the battery pack.

If you want to try this, here are a few things you should know about.

1.
When the timer switches 'off', if your particular charger draws
any significant current from the battery pack you will end up with
a dead battery pack after a certain time. This means before purchasing
a timer you should check the current draw of the charger when it's
unplugged with a full battery pack installed. If it's more then
about 500 microamps, you may not want to use this method, although
it may still work. The 'break even' point is about 2 milliamps, so
if it draws as much as 2ma you wont be charging unless you increase
the charge time to 1 hour instead of 30 mins.
If it draws more then 2ma i wouldnt use it at all unless i was
willing to do some experimentation to determine if charging and
discharging a little more then usual would work in the long run.

2.
Almost any timer on the market will probably work, but it should
be capable of turning off within 30 mins. Some timers only turn off
after 1 hour of operation. While this might work too, i would stick
to the 30 min models only.

3.
This might work with NiMH cells too, but i'd monitor the
cell for the first few weeks. Also, 30 mins might not be
enough time per day for a typical 2Ah NiMH cell.

4.
If your charger is a 'smart' charger, you probably wont have to do
this at all.


RESULTS SO FAR

So far i've had mine on for about a week now, but because the
pack was self discharged for about two weeks im allowing it to
charge twice per day instead of once per day. I've checked
the battery voltage and it's only risen slightly, showing that
it's certainly not going through a full charge 24/7 but that it's
only getting a fraction of it's full charge per day. I expect
this to work very well. I'll switch to once per day soon too.
I'll try to remember to post any further results also, perhaps in
6 months or so.

Take care,
Al

I started using a timer at least a year ago. It STILL didn't help my truck drill... ALWAYS dead when I needed it!

Also I didn't use a timer as you say, instead using it to keep from overcharging batts during the workday or overnight.

I did have a thought to use the timer as you suggest not more than a couple days ago. It was to be so my Dad didn't kill his new drills batteries TOO fast. But the new drill came with a 'smart' (at least internally timed, PERHAPS current controlled) charger. Though I don't have a clue how it outputs in trickle mode.

I guess great minds think alike... LOL! I'm FAR from having a great mind!!!

Al,
Are you a linux or unix user? How come you are going like < 80 characters per line ? /ubbthreads/images/graemlins/grin.gif

Which 'another site' are you luking around huh /ubbthreads/images/graemlins/poke2.gif

If the charger sucks some current from the battery when not charging, can we add a diode to prevent the current flowing opposite way? I built a solar panel that way I think. Does it work? Will Void warranty!

Vince.

I've never used one, but you could also try the Lil' Trickler.

Hello again,

PJoe:
You dont have to use the timer with a smart charger.
Not all drills come with a smart charger however, so
the timer works out without altering the charger itself.

Vince:
Im not using linux yet, but i hope too.
Why, is <80 characters per line a problem?
You might be able to add a diode, but you'll have
to check the full charge current to see if it's
gone down too low. Adding a diode in series reduces
the output a little so it has to be checked.

Empath:
Nice looking unit, but a little pricey dont you think?
The timer costs $5.00 USD at Home Depot, but are available
almost anywhere for about the same price.

Take care,
Al

I don't understand the way that Lil' Trickler works. The FAQ sounds like double talk. Can anyone fill me in?

Paul

Regarding the Lil' Trickler...

This doesn't look like a timer-type trickle-charge device. Something tells me it's a current limiter or possibly even a TRIAC-based dimmer-type circuit! /ubbthreads/images/graemlins/icon15.gif

The sentence that reads "The lights on your chargers will either glow dim, or not at all." makes me wary. This would probably work fine for true "dumb" chargers that have little more than a transformer, resistor, and a diode in them, but I wouldn't dare plug anything with a switching power supply in this box. It would be interesting for someone to buy one and document what's really inside.

*Looks for guinea pig* /ubbthreads/images/graemlins/grin.gif

Abit off topic,
Al, < 80 chars per line is not a problem at all. But > 80 chars is a problem for some linux/unix users out there because a standard terminal is set to 80 chars per line, and text looks ugly when they get wrapped.

Thanks for the advice on diode.

Vince.

I was browsing around some R/C sites and I found this at Red's R/C Battery Clinic.

Basically they talk about exactly the same thing MrAl spoke of, just thought I would throw it in for redundancy. They talk about 1/24th the rate of your charger (1 hour out of a day) but this calculation is for slow (12-16hr) chargers.

Also note his remarks regarding continuous trickle charging versus higher-current pulse charging. The dendrite formation in NiCd cells is a function of total charging time, NOT average current density...so, a 10% (or less) duty cycle at a proportionally faster charge rate will reduce the likelyhood of "soft shorts" forming.

Oh, and I offer this information as long as MrAl signs a virtual NDA to keep him from revealing said information to this "other site" he thinks he posted on. /ubbthreads/images/graemlins/tongue.gif /ubbthreads/images/graemlins/grin.gif

Hello again,

I didnt read up on the Lil Trickler so i cant comment on that, sorry.
It's price seemed a little high for what i needed.

Vince:
Thanks for the info regarding linux users. Maybe i'll try to keep
my lines less then 80 characters. I try not to let them get too
long as it is, maybe out of habit from the older text editors

JSWright:
Guess what? The timer i picked up is just that brand name too,
Intermatic
The only thing i dont like about that brand is that if you pull
the little tabs out you could easily loose them. They dont stay
on the timer unit itself, but rather pull free. Other units i've
seen the tabs stay mounted to the timer at all times, even if not
used to turn on/off.
The way i determined the charge time is as follows:
A NiCd losses about 1 percent of its charge per day.
For a 2 ampere hour battery (approx type used in drills)
that equates to 2/100 or 0.02 ampere hours per day.
The charger puts out roughly 100ma all the time, so
in one hour the battery gets 0.1 ampere hour of charge.
Since this is 5 times as much as needed, dividing one
hour by 5 results in a timer period of 12 minutes.
To make up for the inefficiency of charging a NiCd
12 minutes gets multiplied by 1.4 which gives 16.8 minutes.
Since the timer had increments of 30 mins each, i could
only set it to 30 minutes so that's what i did.
If the 1 percent quoted above is inaccurate (as it probably
varies from battery to battery) lets say it can be as
low as 0.5 percent per day to 2 percent per day tops.
This could lead to a required charge time of from
about 8 minutes min to 33 minutes max. I still think
30 minutes will be ok, but im monitoring the battery
for a few weeks, and after maybe two years i'll monitor
it again to see if it's self discharge increase much.
If it does, i might have to go to the full hour.

I guess it should be noted somewhere that for a 4 ampere hour
battery all these time periods have to be doubled too.


Take care for now,
Al