How much voltage is too much?

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Zebretta
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How much voltage is too much?

I have a new battery pack consisting of 12, 1.2v NiMh sub C cells

The OEM charger for this pack is 21v, 250mA…but I was using a 24v, 400mAh charger
BUT..the OEM battery pack was NiCd cells (1.2v X 12 sub C)

Problem is, it seems the voltage is dropping instead of going up during the charge cycle. Full charge is indicated by a red light turning to green.
After 24hours charging it has not turned green and the voltage I measured this morning was higher than it it is now after about 5 more hours on charge.

Is 24v @ 400mA too much for a 14.4v battery pack?

Edited by: Zebretta on 02/11/2017 - 19:02
Lexel
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NiCd and NiMh are not charged with a constant voltage if you dont want to trash your batteries quick

Read about delta V charging
http://www.ansmann-energy.com/en/charging-systems/charging-technology/32...

Taking NiMh hot from charging they get about 1.5V, resting after a couple hours later at 1.4V then slowly get to 1.35V over next days

If you charge em with 21 or even 24V you cook the batteries dead

If you dont charge em with delta V you should use 1.5V tops per cell and only charge em
Time=capacity/charge current*1.4
Charging too long kills the battery quick by overcharging

So for a 12×2Ah battery pack simple charge at 400mA
18V and 7 hours
The batteries wont get 100% full but you avoid bad overcharging

Enderman
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You need to buy a proper battery charger…not just hook them up directly to a constant power source.
The batteries are probably already damaged from charging like that.

Zebretta
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I located the OEM 21v, 250mA charger. But the device now has NiMh cells instead of NiCd cells

Lexel
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There is no difference between NiCd and NiMh charge characteristics or voltage

If you dont use a smart charger you damage the batteries and they wear out fast especially when overcharged

There is no fix voltage you can plug the battery to and it will charge to 100% and stop

A lead acid battery can be plugged on a fix voltage and it will not harm the batteries life
lithium can be charged with a constant voltage, but if the battery is full you need to unplug it otherwise it wears down the cell
NiMh batteries need a smart charger which can detect the voltage drop and terminating the charge, if not termination it will wear down the cell really bad

hank
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Zebretta
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Enderman wrote:
You need to buy a proper battery charger…not just hook them up directly to a constant power source. The batteries are probably already damaged from charging like that.

Odd because this is a Hoover rechargeable floor cleaner and I’m using the OEM charger that came with it.

Lexel
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There are junk chargers which wear down he battery fast if plugged in too long

A decent charger costs money and often cheap products just use a junk charger to maximise profit

Zebretta
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Lexel wrote:
There are junk chargers which wear down he battery fast if plugged in too long

A decent charger costs money and often cheap products just use a junk charger to maximise profit

You’re probably right. It’s in their best interests if I have to buy another $150 floor cleaner or at least a new battery pack sooner.

Zebretta
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I guess I could use one of my hobby chargers…..I think.
I have an iMax B6 mini that hardly gets any use.

At least they measure Delta V and have cut out circuitry.

mrheosuper
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watch out those imax, i used to have one imax b6, and it over charge my Ni-mh pack( overnight, the pack was too hot to hold long by hand)

Forgot my pen

Zebretta
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mrheosuper wrote:
watch out those imax, i used to have one imax b6, and it over charge my Ni-mh pack( overnight, the pack was too hot to hold long by hand)

I think that’s an issue with the Chinese knock off ones and not the authentic SkyRC units.
I’ve had 3 of the authentic SkyRC units and never had that problem although the flimsy USB data ports failed on all 3

Enderman
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Zebretta wrote:
Odd because this is a Hoover rechargeable floor cleaner and I’m using the OEM charger that came with it.

They do that so they save cost and you can buy a new vacuum after a few years.
Buy a hobby charger to charge batteries properly.
The closer the battery is to charged the less voltage it provides so that you can fully charge the battery without exceeding or damaging it.
Angler
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Zebretta wrote:
Lexel wrote:
There are junk chargers which wear down he battery fast if plugged in too long

A decent charger costs money and often cheap products just use a junk charger to maximise profit

You’re probably right. It’s in their best interests if I have to buy another $150 floor cleaner or at least a new battery pack sooner.

You will notice that in the instruction for appliances like this (nicd or nimh powered hand vacuums, cheapo toy rc cars, bargain basement rechargeable drills) they ALWAYS say unplug the device as soon as it is charged. They cheap out on the charger and it will damage the battery if left on the charger. Hoover rechargeable floor cleaner falls into this category.

Zebretta
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gauss163 wrote:
Zebretta wrote:
I think that’s an issue with the Chinese knock off ones and not the authentic SkyRC units. I’ve had 3 of the authentic SkyRC units and never had that problem although the flimsy USB data ports failed on all

Calling SkyRC “authentic” is funny. They too are a Chinese cloner (of the original Bantam – a South Korean company).

I see your point. Didn’t know SkyRC was just another knock off of someone else.
I do know that SkyRC will ignore you if you have a problem during the so called “warranty (joke)” period.
Unless you get the seller you bought it from to help you you’re SOL

Zebretta
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Welp,
I tried using my hobby charger but no luck….

Every time I tried to charge the battery pack I got an error that said “Connection Error, Check Main Port”.
The User Guide says this error means the battery connection is wrong.
I tried NiMh and NiCd and got the same error. There is no balance port connection for this NiMh battery pack….(obviously)
It’s 12 NiMh cells connected in series. So the charger is thinking 1.2v but it’s actually 14.4v.
It might work if I charge it as a 4S LiFe because that is 14.4v

I checked it every way possible and everything was fine. My conclusion is that there is some circuitry in the appliance itself that is preventing the hobby charger from working with it. The only way I think I could use my hobby charger to charge this battery pack is to remove it every time I want to recharge the pack connecting directly to the battery pack….. and I’m not doing that.

When I plug in the OEM wall charger it charges normally.

So, I’ll just leave it plugged in over night after using it and unplug it in the morning. If it slow cooks the batteries oh well.

Enderman
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Usually hobby chargers are limited to 8 or 10 nimh cells…
You also do not need a balance port, nimh batteries only need to be connected with the + and – and the charger can auto detect what voltage to charge to.

snakebite
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sounds like the charger is not seeing the smaller drop at full of nimh.
charging the pack with your b6 will help it live longer.

Lexel
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the Imax B6 can charge up to 15 NiMh cells

so you plug the power supply in the wall charger, but connecting the Imax to the wall charger gives an error

there must be some sort of circuitry in it, but measuring lower voltage after 5 hours additional charging means it has no smart charger built in overcharging the battery

also the voltage drop of NiMh cells is 40% smaller than on NiCd ones so the charger may miss termination

Zebretta
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thanks for all the assistance.

it has been helpful