Batteries

[Max]

The sellsman told me that there isnt enough current for LM317!
And advice me to try with 20 ohm resistor,because the power is about 16V I think and the current 0,05!He told me 18 hours!And that this type of battery cant be damaget this way/overcharge/!
What you think?

Hi,
I think that if there is NIMH label on them then you can easy damage by overcharge... expecially when charge rate is above C/10.

Now if your output from supply is 16V and limit resistor is 20ohm you get (considering zero the internal resistance of battery pack... actually about 0.1 ohm per cell typ):

(10volts is about less you can get from working pack of ten NiMh undamaged at maximum discharge)

(16-10)/20 = 0.3ampere

Your C is 700mAh then 0.7Ah, so you charge at 0.3/0.7 = 0.42C that is more than four times the C/10 safety limit... so you'll damage everything.

The salesman do what he knows: selling stuff.

Let the electronics be played here... where marketing have no meaning.

Kind regards,
Max

hi

The sellsman told me that there isnt enough current for LM317!
And advice me to try with 20 ohm resistor,because the power is about 16V I think and the current 0,05!He told me 18 hours!And that this type of battery cant be damaget this way/overcharge/!
What you think?

[Max]

Hi,
Max.
I try charge only with 20 ohm resistor conected to + of Ac/Dc adapter and now batteries are charging!
But I have noticed that they cant last long?
Why?
And when charged they show 13,8v and when playing with them they drop very quick I think no more that hour!When voltage reach 12,4 it sudenly begin to drop too fast and there isnt enough power for device to work!
What do you think?
Please help again

Hi,
your battery pack have capacity of 700mAh right ?

I suppose you adapter give you 15-18v dc... ok if so with 20ohm you'll have a current limit of 0.75 to 0.9 Ampere... no good... that way you have probably damaged your batteries... the fact they don't charge well and don't give you enough capacitance (discharge too fast) means the capacity of batteries dropped under 700mAh.

That could happen cause of not reversable reactions inside the cells during overcharge. If so the internal resistance of each cell is now higher than of a working battery-cell.

If all that happened you battery are permanently damaged.

I saw it on old NiMh cellphones batteries cause of simple chargers used in the past.

Best regards,
Max

[tiktak]

hi

Hi,
Max.
I try charge only with 20 ohm resistor conected to + of Ac/Dc adapter and now batteries are charging!
But I have noticed that they cant last long?
Why?
And when charged they show 13,8v and when playing with them they drop very quick I think no more that hour!When voltage reach 12,4 it sudenly begin to drop too fast and there isnt enough power for device to work!
What do you think?
Please help again

[Max]

This man told me that maybe the battery is not dead,maybe it cant suply the device because dont have enough ampers???
I dont have internet now and go to a local internet cafe to write so please help man.
I have two batteries and cant go fieldtest damn!!
He told me that my ac/dc adapter should give 1,5A?!!?!?
Can wate to test TGS.

Hi,
300 mA current is enough if you charge at e.g. 70mA (C/10).
So, I think this is not your problem.

About resistance you have to do 1.25/current-limit-in-ampere:

1.25/0.07 = 17.85 so about 18ohm

This apply to a charge at C/10... then for 10hours charge

If you want 12hours:

1.25/(C/12) = 21.42 ohm about 22

It's not a good idea exceed too much with current charge or time with NiMh... so if you calculate e.g. for 10hours be sure removing the batteries after maximum 11-12hours.

I suggest you stay on the specs... and do maximum 5% overcharge time...
for 10hours -> max 10 hours and 30minutes at limit 0.07ampere, cause is much more safe.

Continuos overcharging (trickle) is possible at C/10 but it's probable will damage batteries after few time (e.g. 4-6hours more than expected time).

Best regards,
Max

[tiktak]

This man told me that maybe the battery is not dead,maybe it cant suply the device because dont have enough ampers???
I dont have internet now and go to a local internet cafe to write so please help man.
I have two batteries and cant go fieldtest damn!!
He told me that my ac/dc adapter should give 1,5A?!!?!?
Can wate to test TGS.

[tiktak]

Hi

Hi,
Max.
I think I found the problem!
On my ac/dc adapter is labeled that it gives 300mA MAX!!!!
Isnt this too low?
Someone have told me that maybe my curent is not enough!
He told me that for charging 1 cell NI-MH I need up to 20% of the curent,BUT he also ask me have I think that they are 10?So?
I realy dont now how to proceed!!!
I have my TGS ready,2 coils almost ready,BUT dont have suply to go make fieldtest!
PLEASE TELL ME SHOULD I USE OTHER VALUE of resistor attached to first charging circuit that you give me/LM317T,1N4007,20ohm resistor/.
Thanks man hope reach your results soon.
Be well.

[Max]

Hi tiktak,
when you have to discharge NiMh cells and need to know what's e.g. residual charge
or for how many % have you discharged them you can look at discharge curves.
There you see something xC means x-times capacity discharging current (constant)...
then can find out voltage for a particular level.

Now come back to the problem: you need 80% discharge and in few (20-30) minutes.
Suppose you use a 10ohm resistor 30W (big and with metallic heatsink)... you get
about for 10cells 15v, then:
15/10 = 1.5Ampere
power dissipated is about 22W, so resistor become hot... and maybe you need additional heat
sink.
You can use also e.g. 2x 20ohm 20W each resistors in parallel, same thing, runs cooler.
Or also an old car lamp at 12V... find one that need 1.2 Amper (15w): 10ohm and lot of watts

OK now you know which current you have discarging cells:
with 10ohm resistor -> 1.5 A
with lamp -> 1.5 A the same
OK , now 1.5A/C = 1.5/0.700 = 2.14
You're discharging at 2.14C
Now look at the picture you'll have each cell deliver something like 1.08V at 80% discharge
with 2C rate, so you have to espect a bit less voltage, we don't need exact values, say it's
1.06V for cell.

Of course, discharge current isn't constant... but is a good estimate.

OK now you know what to measure, during discharge to know what's going on and if cells are at
80% discharge : look at voltage for the pack 10, 10*1.06 = 10.6V
When voltage of the pack drops under 10.6v with load attached you actually have discharged more
than 80%, so then you can start charging them.
Easy.

So you have just to put the resistor(s) or lamp I've indicated directly on the pack output, and watch at measured voltage accross
load using multimeter. That's it.

If use lamp you have also a visual indication of discharge by intensity of light.

Kind regards,
Max