# What ac voltage voltage to charge a 4.8v dc chargeable battery pack.

Discussion in 'Technical Repair' started by Roque, Oct 2, 2016.

1. ### Roque Thread Starter Member

Sep 16, 2014
132
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Helloo gurus got a Andis charger to fix ...was initially 110v ac ..was plugged in 220v ac and the tranny has fried. What secondary ac v would i need to charge a 4.8v dc chargeable battery pack. Should the voltage should be higher than 4.8vdc or ??? Any help would be much appreciated.Ta.

2. ### ci139 Member

Jul 11, 2016
341
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You dont wan't to overcharge Ni-Cd (explodes emediately) Li-Ion(explodes later few days to w about a week !!!)
so you better use a quality "off the shelf" charger

otherwise the wall transformers have a property of giving a "better performance" on "higher loads" (output Watts) -- tough they heat up and may burn their primary´s protection more likely (at higher loads) -- so the power drawn from 2-ry should be not too excessive . . .

the stats. (my stats.) show
• the higher the impedance (more turns) for 2-ry the better the efficiency (best voltages ratio roughly 10 to 15 e.g. ~240V / apx.12 = ~20V)
• it is useful/practical for the linear (voltage) regulators' input to have the 2-ble output voltage (@) "zero load"
e.g. for 4.8V regulated OUT you need DC 9.6V (@ no load in) = ~AC 9.6V / (1.1 to 1.6) = 8.7 down to 6 V ~AC on secondary (before **FULL WAVE rectifier -- only applies for***)
-- as P = U²/R -- we assume average ²√(8.7² + 6²) = 7.5V ~AC out for secondary minimum (although for no surprises use value more close to ~9V)
• use Litz wire for secondary if such fits there (improves efficiency and thermal parameters)
!!!!!! you still need to make abs(shure) you wont overcharge your rechargeable pack !!!

3. ### hp1729 Well-Known Member

Nov 23, 2015
2,306
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Or just charge from the USB output. Use a 100 ohm resistor, or so, in series with the battery and be patient.

4. ### Roque Thread Starter Member

Sep 16, 2014
132
2
Thank you for your reply the secondary voltage of the transformer which i have is 12v Ac and the output at the 4 charging points after all the circuitry is 12vdc on two points and 14vdc at the other two points ...was wondering why the different voltages ...havent tried placing in the clipper unit as i will have it in hand on tuesday..is it worth the effort or shpuld i request my mate to buy a new one? As the exploding part you mentioned sounds scary!!. Thanks once again.

5. ### Roque Thread Starter Member

Sep 16, 2014
132
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Hi mate thanks for your reply it has got no usb out. Will post photos cheers

Sep 16, 2014
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7. ### Roque Thread Starter Member

Sep 16, 2014
132
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Thats the new tranny the fried one is just about the same size ..little smaller though.

Sep 16, 2014
132
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9. ### Roque Thread Starter Member

Sep 16, 2014
132
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The original tranny

10. ### ci139 Member

Jul 11, 2016
341
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for 4.8V battery the 12 and 14V sounds too high (plugging a battery into possibly faulty charger is not a good idea)
▲this is the trigger of the following▲
GBP 85.00 = EUR 98.14 -- it does not look "unaffordable" (building a "wrong" charger or even the right custom charger may be more expensive)
http://simpsons-online.co.uk/shop/andis-agr-cordless-clipper-charger/
those guys have a phone listed
ask if they can test OR/AND repair/"replace" your charger (of course the cheapest option of least - where i live we must know and guide (by hand) everything everybody yourself e.g. sales men repair service -- it's like "do 1 , do 2 , ...")

i don't want to start inventing a bike here yet

Last edited: Oct 2, 2016
11. ### Roque Thread Starter Member

Sep 16, 2014
132
2

.Thanks mate. Cheers.

12. ### ci139 Member

Jul 11, 2016
341
39
ups! - there's actually a second thought
as how you measured the voltages (please be cautious not to short nearby conductors)
- namely there are 4 terminals -- and i donno their function

-- if your voltages are referenced to the NEG GROUND of the rectified part of PCB
then 14V – 12V would give you 2V difference for battery pack terminals in which case it might not necessarily be an indication of an error ------ there was stated in the web such battery packs use sections of 1.2V sets --- which in your case may be 2× 2.4V banks --- if its true you should be get those voltages measuring the pairs of your terminals on battery pack e.g. there should/could be 2 distinctive pairs as:
terminals/voltages
ABCD - random labelling of terminals on B-Pck
A to C 2.4V ,C to A -2.4V
A to B 0V , B to A 0V
A to D 0V , D to A 0V
B to D 2.4V , D to B 2.4V
similar for charger side only instead of 0V there may be something else
theres no much point to measure it - i have to look up the schematic from web as the model of your hardware is actually known ......... just what you should expect

(you listed 4 voltages) assuming you'd know the NEG battery terminal
you should have been listed 3 voltages or 3 voltages and 0V for (–) battery terminal ??????????????

Last edited: Oct 2, 2016
13. ### Roque Thread Starter Member

Sep 16, 2014
132
2

From the 4 terminals theres 12vdc across two terminals and and 14vdc across the other two..that is when i connected the 12v ac transformer .the model of the charger is Andis AGR+/BGR+ searched high and low couldnt find a schematic ..also rang Andis in the US but no joy..the lady wasnt so helpful...out here in Australia i dont know who the dealer or service centre is. If you get lucky with the schematic pls do let me know thanks again..regards. Roque.

14. ### ci139 Member

Jul 11, 2016
341
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it's from oz to uk / us but the return direction likely same +customs(if any) +inside oz (was just curious)

ok this shouldn't get too lengthy
you need to find out whether your stand/charger got hit by momentary over voltage (before the transformer failed)
if so buy local or foreign (® or substitute , a) new one / the batteries are std. -- so anything that charges the (4.8V or 2× 2.4V or 4×1.2V) Li-Ion or Ni-Cd (whatever you have) charges it in principle the same -- no matter the manufacturer and it's locale e.g. you use your old stand for charging contacts (making the connections to from new one (cutting connections off from old PCB if it's faulty) so the new one can be used as is if the connections are removed) ← if it does not make make sense ask your friend (i suggest onsite solving much more quicker error proof - than anything remote) or ask me questions (remote slow/time-inefficient)

15. ### ci139 Member

Jul 11, 2016
341
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there is another option - somewhat - unusual - but not - as "we" worked
you call Andis and ask if they can remotely assist your test and or repair (if you have anyone more "qualified" to such loacally agree schedule the event - so to keep the \$/h rate low) - for agreed \$/h - everithing (mail info exchange) we did here you do with them coz their product not well documented in internet

or it can be done slow ((= you make a set of good quality pictures of your PCB test out your Battery pack cfg. e.c. , e.c. ... and finally we may find out you need to buy a new item or not ? worth to waste the time for ?))

... or likely best is find your local oz "Andis aware" person (who knows the hw - coz i yet don't , it's a time - not to waste for nothing - if you learn something it's worth to waste to enough to learn it good)

Last edited: Oct 3, 2016
16. ### ci139 Member

Jul 11, 2016
341
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the problem is i've never seen 4 terminal battery packs - so i donno anything about them
those guys provide the peek inside - but it's likely a different model/configuration

17. ### Roque Thread Starter Member

Sep 16, 2014
132
2

Thank you for all the info you provided. As you have mentioned is it worth the time and effort makes sense ....i have called my mate to meet up this evening and bring the clipper along with him ..will try connecting the charger to the unit using the earlier mentioned 12v ac transformer ..if it works well and good ...if not getting one locally would be the way to go..like you mentioned yes its very strange to have 4 terminals .. ...i have also checked my cordless dewalt drill which has a 7.2 v battery and i measured the dcv in the charger (drill charger)and it showed 35vdc thats a big difference...so the 12v and 14v might be appropriate or no is the question...if i may ask you how would i know if the andis charger would be charging fine once i connect it ...or not ...or if it may explode or?? I guess its a matter of time ..??

18. ### ci139 Member

Jul 11, 2016
341
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actually the usually explode softly after overheating (pass out gasses of High-temperature electrolysis)
but if left "charging" overheated they might and pop off the cap or even "explode"
Li-Ion
NiCd -- they don't mention it (but i detached my custom quick-charger (forgotten ON for multiples 20 minutes) seconds before the caps poped off - it was quite scary)

• the charging current for not very exhausted batteries is 300mA or less
• if you use an impulse type of charger - then i can't tell you - (it's like they use a safe-proven method of next)
• if the charger voltage is too high the batteries will overheat in seconds (less than 10)
and usually you can see/hear a spark between contacts at connecting (overheating has a timeconstant through the plastic casing - so - if you plug it in for 2 to 3 seconds and pullout then after the 20 30 s the heat reaches the surface of battery pack - if by first impression this surface feels even slightly hot - over 38°C/100°F - then it's not good)

the master fault indication is the battery gettin hot too fast
usually it gets warm at the end of the charging cycle - after an hour minium usually 4 or more (if not pulse or quick charger)

this is why it is better to let the person who knows that exactly to supervise or do this

Jul 11, 2016
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20. ### ci139 Member

Jul 11, 2016
341
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https://www.maximintegrated.com/en/app-notes/index.mvp/id/4322
is how it's done more correct for constant current constant voltage charger
(items to notice)
https://www.maximintegrated.com/en/images/appnotes/4322/4322Fig01.gif
the empty battery not being charged with high current until it develops ability to generate some voltage internally
followed by Const.Current then by Const.Voltage cycles (not exceeding critical 4.2V)

more about LI-Ion http://www.powerstream.com/lithium-ion-charge-voltage.htm

http://www.cadex.com/en/batteries/safety-of-lithium-ion-batteries

basically use more sources for help as just here (http://forum.allaboutcircuits.com)