DPL 8 and NiCad charge problems - RC Groups
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Feb 06, 2017, 06:55 PM
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Help!

DPL 8 and NiCad charge problems


I have been unable to get my DPL8 to charge my Ni Cad and NiMh batteries completely, the charge always charges a 4 cell 4.8 volt pack to a maximum of around 5.4 volts i have tried using the bump charger in manual mode using the software presets always with the same results. If i start the charge again it will charge a bit more and then quit again. I set the max cell voltage to 1.55 volts using either charge method so it should give me a fully charged pack with 6.2 volts which i cannot seem to achieve. The charger does a great job on LiPo's but not to well on my Ni Cad and NiMh batteries.

I am wondering if the peak detection is so sensitive that it terminates the charge and if so can i make it a bit less sensitive. i have attached a picture of the bump charger at charge termination, one of the screen from a tablet with the software and a picture of a battery tester.
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Feb 07, 2017, 01:19 PM
Registered User
Quote:
Originally Posted by steve51
I have been unable to get my DPL8 to charge my Ni Cad and NiMh batteries completely, the charge always charges a 4 cell 4.8 volt pack to a maximum of around 5.4 volts i have tried using the bump charger in manual mode using the software presets always with the same results. If i start the charge again it will charge a bit more and then quit again. I set the max cell voltage to 1.55 volts using either charge method so it should give me a fully charged pack with 6.2 volts which i cannot seem to achieve. The charger does a great job on LiPo's but not to well on my Ni Cad and NiMh batteries.

I am wondering if the peak detection is so sensitive that it terminates the charge and if so can i make it a bit less sensitive. i have attached a picture of the bump charger at charge termination, one of the screen from a tablet with the software and a picture of a battery tester.
Steve,

Typical NiXX "full" voltage (where delta-V occurs) is typically in the 1.35-1.45v range, so your 1.37v/cell result isn't really unusual.
Note that the 1.55v shown is really just an upper safety limit - it is not used to determine when the pack is full - NiXX charge termination always uses delta-V detection.

The Bump Controller uses delta-V value of 8mV/cell for NiCd and 5mV/cell for NiMH - these are the default values used in the PowerLab NiXX presets also.

The ability to adjust delta-V as a setting in the BumpTag is also on our future feature list, but not currently a high priority - if folks are seeing problems getting complete charges, then that will certainly raise the priority of that feature.

Do you typically see a higher termination voltage when charging with a different charger ?
Are the cells warm to the touch when finished (i.e., you know they really are full) ?
What happens if you immediately restart the same charge ... what do you notice about the voltage and warmth then ?

For purpose of narrowing down the root cause, it might be worth trying the PowerLab NiXX presets without the Bump Controller, and adjust the Fallback (delta-V) voltage to something higher to see if that helps.

Let me know what you find - we obviously want to make sure that NiXX works well.
Feb 15, 2017, 04:30 AM
Registered User
Quote:
Originally Posted by steve51
I set the max cell voltage to 1.55 volts using either charge method so it should give me a fully charged pack with 6.2 volts which i cannot seem to achieve.
Quote:
Originally Posted by RevoKelly
The Bump Controller uses delta-V value of 8mV/cell for NiCd and 5mV/cell for NiMH - these are the default values used in the PowerLab NiXX presets also.
I experience the very same issues Steve has mentioned but with my PL8's.

I'm pretty certain that the relatively low delta V setting is the culprit or the fact that the charger maybe acting too fast on the delta V reading and terminating the charge.

I have even tried adjusting this value to the max allowable on the PL8 yet my batteries peak detect too early in their charging phase as the batteries do not get warm at all yet the charger terminates the charge as complete.

This is quite noticeable where the cells are situated in a battery holder rather than soldered together no doubt due to slightly inconsistent contact between the battery and the tabs of the holder which can cause the delta V voltage to fluctuate more.

In many cases I resort to using some old Swallow battery chargers to charge my NiMh batteries as they use a much higher Delta V setting (around 20 to 40mV) which tends to charge the packs more consistently as you can note a slight temp rise in the cells when finished.

I think Sanyo from memory recommend a 5 to 10mV Delta V setting for their NiMh cells.

As I alluded to before - It may not be so much that the actual delta V setting requires increasing in the charger itself but maybe that the averaging function (not sure if the calculated delta V is averaged over a certain time period or not) for the measured delta voltage is increased somewhat so that it will not peak as quickly...?
Last edited by Costas_; Feb 15, 2017 at 04:42 AM.
Feb 15, 2017, 10:24 AM
Registered User
I'll pass that data along to our PowerLab team to add to the list to investigate.

As you said, nearly every manufacturer recommends something very close to 5mV for NiMH and 8-10mV NiCD, so drastically raising the deltaV detection might help, but can't really be the root cause and shouldn't be required.

I'll raise the priority of getting Fallback (delta-v) voltage adjustment support in the Bump too.
If nothing else, it will let folks test with higher deltaV values and see whether or not it helps in their situation, which is valuable data to have before making other changes.

Also note that cells that are mismatched or drained independently results in their level of charge being quite different, causing them to deltaV-peak at very different times which also makes detection more difficult and more prone to early termination.
If you are draining NiXX cells independently, then they should be charged independently (single cell), as opposed to placed in a holder.
I suspect that you are actually draining them together, but just pointing that out for others.
Feb 15, 2017, 10:45 AM
Registered User
How old are the NiCads being used here? Also, what is the make/model of NiCads being used? AFAIK, NiCads haven't been manufactured in recent years so it's possible these cells are beyond their end of life.


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