Go Back   Steve's Digicams Forums > Digicam Help > Batteries or Power Packs

Reply
 
Thread Tools Search this Thread
Old Aug 14, 2003, 2:16 AM   #1
Junior Member
 
Join Date: Jun 2003
Posts: 20
Default Battery Charger question

Will my battery charger with an output rating of 1800mA charge 2000mAH batteries to their full capacity? Or do I need to get a charger with a higher rating?
Welshman is offline   Reply With Quote
Sponsored Links
Old Aug 14, 2003, 4:06 AM   #2
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

That's just a measure of current, IMO it will charge any higher capacity battery of the same type just fine (but might take longer at it). A slow charger which only put out a fraction of that output, as an example ~100mA will take slighly over (2000mAH/100mA=) 20 Hrs! ie the output voltage is still around 1.2V per cell...
NHL is offline   Reply With Quote
Old Aug 14, 2003, 4:21 AM   #3
Junior Member
 
Join Date: Jun 2003
Posts: 20
Default

Thanks for your speedy and informative reply, NHL!

BTW, I like your Gallery...
Welshman is offline   Reply With Quote
Old Aug 14, 2003, 4:34 AM   #4
Senior Member
 
Join Date: Aug 2002
Posts: 2,162
Default

Actually, the answer can be a bit subtle based on charger marketing hype claims. The charger may come with 1800mAh batts and say it charges them in X hours. For example a charger actually producing 1800mA will theoretically charge a 1800mAh batt set in 1 hour. However the manufacturers often don't mean this.

If your charger supplied with 1800maH batts says it takes about 4 hours to charge them, it's actual continuous output is only about 450mA.

If you put in bigger batts, the maximum charging current stays the same, but charging takes longer. So, if you put in 2400mAh batts they will still charge to full capacity, but would take approx 2400/1800 X4 = 5.3 hours (or 32% longer).

So when buying a charger, the biggest one in current terms (and better scaleable to newer larger batts) will be the one with the SHORTEST quoted continuous charging time for the LARGEST quoted battery size capacity. VOX
voxmagna is offline   Reply With Quote
Old Aug 14, 2003, 5:35 AM   #5
Senior Member
 
Alan T's Avatar
 
Join Date: Jun 2003
Location: Chester, UK
Posts: 2,980
Default Remember the waste heat

When working out [charge=charging current x time] we shouldn't ignore the inefficiency of the charging process. This is a lot of energy, as you can tell by feeling the hot batteries.

A lot more than 1800mAh will be put in to an 1800mAh cell on charge, the excess appearing as heat. The energy actually stored in a 1.4V 1800mAh cell is 2.5Wh, so four will contain 10Wh. Given the heat output from the charging process, I wouldn't be surprised if the efficiency is under 50% - think about the heat output of a 10W light bulb (10Wh per hour), and compare it with the heat you get from your batteries on charge.
Alan T is offline   Reply With Quote
Old Aug 14, 2003, 5:56 AM   #6
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

BTW one can tell how good a charger is by how 'hefty' its power supply is... On fast chargers it's usually a separate unit (the absolute rating is usually labeled here by law/agencies certification) and also the most valuable part of a charger!
NHL is offline   Reply With Quote
Old Aug 14, 2003, 11:11 AM   #7
Senior Member
 
Join Date: Aug 2002
Posts: 2,162
Default

............BTW one can tell how good a charger is by how 'hefty' its power supply is...........

Weight and volume is no longer an indicator if it's a switch mode unit. 5 Amps at 12 Volt (60 watts) - enough for plenty of batts - even with inefficiency, is no more than a matchbox! You shouldn't really charge at more than 2hour rate, which means 1 Amp, so that sort of power unit should be good enough for 40+ AA batteries.

I think you'll find the spec/price differentiator is not just the power unit size, it's how they charge the batt's. If each AA cell is individually charged, that's 1 regulator IC per batt. If they charge 4 at a time, that's 1 IC per group.

If you want to charge AA's from your car, the sky's the limit on numbers, you just need lots of regulator chips!
voxmagna is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 12:01 AM.