NiMH overcharge?

[ReeV0]

Hi all,
.
I've just purchased a SkyRC e680 charger and a Zeee 7.2v 5000mAh NiMH battery to use in my Traxxas ex-start.

This morning I charged it for the first time. I set up the charger as per the battery's details - though unlike lipo charging, there wasn't many settings for NiMH mode. Essentially it was just setting the charge rate, which I set at 5A (1c). Though, when I came to actually start the charge, I saw another setting called "NiMH auto charge" which had a charge rate of 3A. I was in no rush and so picked this option, and the charging started.

I'm pretty sure the battery was already 80% charged before it started, but it was still charging after 80 mins. According to the charger, it had put over 4000mAh into the battery. At 90 mins, a warning came up that said "battery overcharge" (or something like that). Seems it has a safety cut-off of 4200mAh, that I can't find any way to adjust.

Is there anyone who has experience with this charger, who can pinpoint what went wrong?

Many thanks to all

 

[zeus r/c]

Hi all,
.
I've just purchased a SkyRC e680 charger and a Zeee 7.2v 5000mAh NiMH battery to use in my Traxxas ex-start.

This morning I charged it for the first time. I set up the charger as per the battery's details - though unlike lipo charging, there wasn't many settings for NiMH mode. Essentially it was just setting the charge rate, which I set at 5A (1c). Though, when I came to actually start the charge, I saw another setting called "NiMH auto charge" which had a charge rate of 3A. I was in no rush and so picked this option, and the charging started.

I'm pretty sure the battery was already 80% charged before it started, but it was still charging after 80 mins. According to the charger, it had put over 4000mAh into the battery. At 90 mins, a warning came up that said "battery overcharge" (or something like that). Seems it has a safety cut-off of 4200mAh, that I can't find any way to adjust.

Is there anyone who has experience with this charger, who can pinpoint what went wrong?

Many thanks to all

I dont havw experience with that charger but i do know that the flat traxxas charger ill send a pic when i get to austin later today but i charge all my batteries off it and not my spektrum g55 charger and have had no problems since i swithed it has 3 charge modes it goes thru on its own its thier trickle charger i think but it charges in 90 mins no matter the pbattery like i say I've had no problems and i dont use throw away batterys anymore i have rechargable servo packs and ez start wand batterys

 

[zeus r/c]

I dont havw experience with that charger but i do know that the flat traxxas charger ill send a pic when i get to austin later today but i charge all my batteries off it and not my spektrum g55 charger and have had no problems since i swithed it has 3 charge modes it goes thru on its own its thier trickle charger i think but it charges in 90 mins no matter the pbattery like i say I've had no problems and i dont use throw away batterys anymore i have rechargable servo packs and ez start wand batterys

This that charger

 

[Tunedfrog]

No worry overcharging a NiMH, it's the lipo batteries you should watch like a hawk.

 

[tudordewolf]

Hi all,
.
I've just purchased a SkyRC e680 charger and a Zeee 7.2v 5000mAh NiMH battery to use in my Traxxas ex-start.

This morning I charged it for the first time. I set up the charger as per the battery's details - though unlike lipo charging, there wasn't many settings for NiMH mode. Essentially it was just setting the charge rate, which I set at 5A (1c). Though, when I came to actually start the charge, I saw another setting called "NiMH auto charge" which had a charge rate of 3A. I was in no rush and so picked this option, and the charging started.

I'm pretty sure the battery was already 80% charged before it started, but it was still charging after 80 mins. According to the charger, it had put over 4000mAh into the battery. At 90 mins, a warning came up that said "battery overcharge" (or something like that). Seems it has a safety cut-off of 4200mAh, that I can't find any way to adjust.

Is there anyone who has experience with this charger, who can pinpoint what went wrong?

Many thanks to all

It's possible the battery wasn't 80% full to begin with and nothing went wrong.

NiMh has a bit of loss where it takes more mah to recharge them than you'll get back out, roughly 80% efficiency I believe, so that 4200mah only added 3300mah of charge. To charge a 5Ah battery you'll want to go into the settings and set a cutoff of like, 6Ah.

New NiMhs (and those which have sat for a while) take a few charge/discharge cycles to "condition", you might want to run it down and charge it up a few times and see if you get more time out of each successive charge.

 

[RustyUs]

Continue what you are doing. The NiMh pack, seeing as its new, may give you better numbers as it is used more often/cycled.

 

[NitroR/C]

Key Differences Between LiPo and NiMH Batteries
LiPo batteries have a clearly defined "full charge" voltage of 4.20V per cell, so the charger knows exactly when to stop.
NiMH batteries, on the other hand, don't have a clear voltage plateau. The charger detects a full charge using the -ΔV method (a small drop in voltage when the battery is saturated). This signal is weak and can be difficult to detect, especially if the charging current is low or the battery isn't new.
Why You Saw More Than 4000 mAh Charged
Your battery is nominally 5000 mAh, so a full charge should, in theory, accept about 4500-5000 mAh (a little less if it was already at 80%).
If the charger kept pumping current, it likely didn't detect the full charge point (-ΔV) correctly.
This is common with new or cold NiMH batteries, or if the charging current is too low to make the voltage drop clearly visible.
The “Overcharge” Warning
The SkyRC e680 has a built-in mAh protection. If a NiMH battery draws more than the set capacity (by default ~4200 mAh, as you saw), it stops the charge as a safety measure. It's not a true error, but a safety cut-off to prevent a missed -ΔV detection.
How to Properly Charge NiMH Batteries with the e680
Set the current manually:
Generally, you should charge at 0.5–1C (in your case, 2.5–5 A).
3 A is a good setting, and 5 A is still acceptable for a 5000 mAh pack.
Avoid "Auto" mode:
The "Auto" mode for NiMH chooses the current on its own, but sometimes it sets the current too low, and the -ΔV isn't detected correctly.
It's better to use the Manual Charge mode and set the current yourself (e.g., 3 A).
Check the battery temperature:
A fully charged NiMH battery will start to get warm (a sign that it can no longer store energy).
If it feels lukewarm or warm, it's a good sign to stop.
Some chargers have an optional temperature probe, which is a great safety feature.
Update the capacity limit:
In the e680's menu, you can change the "Capacity Cut-Off" parameter.
Set it to at least 5000–5500 mAh so it doesn't stop charging too early.
What Happened in Your Case
The battery was already almost full, so it accepted less charge than expected.
The non-optimal current or "Auto" mode meant the charger didn't detect the -ΔV correctly.
The 4200 mAh cut-off was triggered, which is a normal safety protection and didn't damage the battery.
The battery shouldn't have been harmed by this incident as long as it didn't get excessively hot.