Author Topic: Battery charger  (Read 5316 times)

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Offline Blood-manTopic starter

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Battery charger
« on: July 28, 2009, 05:08:51 PM »
i bought an 6v 1400mAh NiMH Battery at ebay: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380124849048 for my $50 robot. I also found old charger. It says 'Output: 6v 600mA. Would it be fine to charge this battery?
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Offline wil.hamilton

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Re: Battery charger
« Reply #1 on: July 28, 2009, 06:27:07 PM »
do you have more information on the charger?
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Offline jamort

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Re: Battery charger
« Reply #2 on: July 28, 2009, 09:14:29 PM »
I'm pretty sure it should work fine... it will just take longer to charge.... so like 2 and a half hours charge time?
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Offline SmAsH

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Re: Battery charger
« Reply #3 on: July 29, 2009, 12:41:41 AM »
and you wont be able to charge to its optimal level...
most batteries use a charging voltage one or two volts higher than their rated voltage to charge.
ever notice how your battery is at 6V5 or 7V when fully charged? thats why :P
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Offline jamort

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Re: Battery charger
« Reply #4 on: July 29, 2009, 12:59:30 AM »
its is fine to charge his battery but not to optimal levels...
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Offline SmAsH

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Re: Battery charger
« Reply #5 on: July 29, 2009, 01:04:52 AM »
yup, thats what i was saying...
just be sure to monitor the battery the first few times of charging... incase it decides to start a fire...
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Offline jamort

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Re: Battery charger
« Reply #6 on: July 29, 2009, 01:11:37 AM »
of course he could always draw a volt offf of a parallel or serial port
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Offline SmAsH

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Re: Battery charger
« Reply #7 on: July 29, 2009, 01:20:53 AM »
your kidding right?
for some odd reason that screams "fried port" to me ::)
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Offline jamort

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Re: Battery charger
« Reply #8 on: July 29, 2009, 01:27:45 AM »
I would think it would work... ive drew power off of one to charge my cell phone before... make two jumper wires one in the v+ and one in the ground... for one volt....

disclaimer im not responsible if this does mess your computer up
« Last Edit: July 29, 2009, 01:31:10 AM by jamort »
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Offline wil.hamilton

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Re: Battery charger
« Reply #9 on: July 29, 2009, 08:39:22 AM »
lol, parallel port.  Seriously, does anyone still have a computer with a parallel port?  Even a serial port?  Those are getting rare too, especially with USB now.  there is usb everything.
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Offline jamort

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Re: Battery charger
« Reply #10 on: July 29, 2009, 11:01:06 AM »
i do on my old computer but my new computer no... but i do have a usb to serial converter... and like 6 usbs, sd card slots and a firewire so im good
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Offline SmAsH

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Re: Battery charger
« Reply #11 on: July 29, 2009, 02:49:51 PM »
you bagging on my old pc? lol, 6 years and still running strong (with upgrades).
but even some newer pc's still have serials, my mum bought a laptop at the start of this year and it has a serial port.
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Offline jamort

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Re: Battery charger
« Reply #12 on: July 29, 2009, 05:17:00 PM »
I know hps dont have them on there computers anymore... of course to get a good computer you have to build it yourself... the average large company(dell, hp, etc.) needs to be upgraded with in three years because there built to make you repair or have to buy them right after the warranty goes... main reason is money...
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Offline Soeren

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Re: Battery charger
« Reply #13 on: July 29, 2009, 06:04:02 PM »
Hi,

Quote from: Blood-man on July 28, 2009, 05:08:51 PM
I also found old charger. It says 'Output: 6v 600mA. Would it be fine to charge this battery?
It depends...
If you by chargrer mean a "wall wart", the 6V marking is the nominal voltage at a load current of 600 mA (well, it's supposed to be at least), and the unloaded output voltage will be higher.
You have to measure the output voltage when drawing say ~10 mA and eg. ~300 mA to find out for sure whether it can be used as a taper charger for your 5-cell battery.

A fresh charged 5-cell nickel based battery will have a terminal voltage of 7.00V to 7.25V right off the charger.
(It will soon go down to ~6,75V after a light loading or after sitting around for a while).

That means that your charger must put out between 7.00V and 7.25V when a load of 10mA to 15 mA is used and you should limit the current if the battery gets over 35°C at any time during charging (if you burn your fingers touching it, you are damaging the battery).

To measure the battery, apply a load of 680 Ohm (1/4W will do). If you get a reading of 7.0V to 7.25V, you can use the charger. Anything less (or higher) won't help.
With a load of 22 Ohm (2W minimum), you can find if the charger has got enough power for the purpose.

Don't ever, even for a second, consider mixing PC port voltages into the equation - that is a ticket to serious disaster.

When you have measured up the charger, post your findings for a go/no-go evaluatiion.
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Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline jamort

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Re: Battery charger
« Reply #14 on: July 29, 2009, 09:46:34 PM »
Quote from: Soeren on July 29, 2009, 06:04:02 PM
Hi,

Quote from: Blood-man on July 28, 2009, 05:08:51 PM
I also found old charger. It says 'Output: 6v 600mA. Would it be fine to charge this battery?
It depends...
If you by chargrer mean a "wall wart", the 6V marking is the nominal voltage at a load current of 600 mA (well, it's supposed to be at least), and the unloaded output voltage will be higher.
You have to measure the output voltage when drawing say ~10 mA and eg. ~300 mA to find out for sure whether it can be used as a taper charger for your 5-cell battery.

A fresh charged 5-cell nickel based battery will have a terminal voltage of 7.00V to 7.25V right off the charger.
(It will soon go down to ~6,75V after a light loading or after sitting around for a while).

That means that your charger must put out between 7.00V and 7.25V when a load of 10mA to 15 mA is used and you should limit the current if the battery gets over 35°C at any time during charging (if you burn your fingers touching it, you are damaging the battery).

To measure the battery, apply a load of 680 Ohm (1/4W will do). If you get a reading of 7.0V to 7.25V, you can use the charger. Anything less (or higher) won't help.
With a load of 22 Ohm (2W minimum), you can find if the charger has got enough power for the purpose.

Don't ever, even for a second, consider mixing PC port voltages into the equation - that is a ticket to serious disaster.

When you have measured up the charger, post your findings for a go/no-go evaluatiion.

what? I was in high school when I did that... lol :P
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my english teacher once said, "dont talk about what you dont know in public...."

so I replied the truth, " Exactly why I dont ever talk about English."

Offline SmAsH

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Re: Battery charger
« Reply #15 on: July 30, 2009, 12:36:53 AM »
the pc port thing? then its fine, just don't do it with your pc :P
the other option is to put a buck/boost regulator into the equation?
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Offline Soeren

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Re: Battery charger
« Reply #16 on: July 30, 2009, 04:44:03 AM »
Hi,

Quote from: SmAsH on July 30, 2009, 12:36:53 AM
[...] the other option is to put a buck/boost regulator into the equation?
Better to make a better charger - I'd suggest the MAX712 a dV/dT-terminating charger http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1666/t/al. It charges from 1 to 16 cells at up to 2A max (and free samples are available).

Look at the app. notes a bit down on the MAX712 page as well (even those using the MAX713), there are stuff to be learned in them.
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Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Weird Fishes

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Re: Battery charger
« Reply #17 on: July 30, 2009, 09:29:55 PM »
Quote from: Soeren on July 30, 2009, 04:44:03 AM
Hi,

Quote from: SmAsH on July 30, 2009, 12:36:53 AM
[...] the other option is to put a buck/boost regulator into the equation?
Better to make a better charger - I'd suggest the MAX712 a dV/dT-terminating charger http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1666/t/al. It charges from 1 to 16 cells at up to 2A max (and free samples are available).

Look at the app. notes a bit down on the MAX712 page as well (even those using the MAX713), there are stuff to be learned in them.


I just got that IC with my last digikey order. =P
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