Charger Varta LCD 57070/57170

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Varta makes both batteries and chargers, here I am looking on a four channel charger with a LCD display.

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I got the charger in a blister pack. As can be seen on the pack the charger needs two hours to charge batteries, but is this correct?

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The pack contained the charger, a power supply, a car adapter, a usb adapter and a instruction sheet.

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This unmarked connector is for 5V and 12V input (The label on the bottom of the charger says 5V and 12V). The charge current is reduced with 5 volt input.

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The user interface is a LCD display with four battery symbols.
With no batteries in the charger no battery symbols are shown, while charging animated symbols are shown and when full filled symbols are shown.

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The charger has the typically two level slots used for AA and AAA batteries.

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Measurements charger


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A nice -dv/dt termination after filling the two batteries. With these two cells it is well below the 2 hour specified time.

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The other channel handles two cells just as fine.

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The Pro cells do looks fine.

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The powerex cells are getting old and there was no obvious termination on this cell, but the charger stopped anyway, maybe because the other cell had a -dv/dt termination or maybe because it reached a capacity limit. The important part is that the charger stopped without overcharging and that is good.

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The AAA cells is charged with considerable lower current, and stops after about two hours when fully charged.

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A full cell is stopped after about 8 minutes, this is also fine.

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With four cell it is revealed that the charger only has one charge circuit and is time sharing between slots. This means double charge time or about 3 hours.

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Using a lap power supply it can be seen the charger uses around 600mA when charging.

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This charger did also include a USB cable and can run from 5 volt, but the charge rate is reduced to nearly 1/3 and this also means 3 times longer charge time. The charger do still terminate perfectly.
This low charge rate means it will work with any usb power supply.

Temp2526

M1: 42,7C, M2: 46,4C, M3: 46,6C, M4: 41,3C, M5: 48,2C, M6: 54,4C, M7: 42,8C, HS1: 55,2C
Both the batteries and the charger gets a bit warm when working.

Poweron

The charger starts in less than 2 seconds. It pauses at regular intervals to check the voltage and do timesharing if charging two pairs. There is a faint audible tick when pausing.

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It is the same on 5 volt usb, except the charge current is lower.

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With four cells the charger will timeshare the charging current between the two pairs.

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5 volt usb looks exactly the same, except, of course, the current is lower.

Measure

Not all pauses are the same size, some are a bit wider. My guess is that the charger only measures voltage in these wider pulses.

Trickle

Trickle charging is done with pulses at low current. The average current during the pulse is about 140mA, when calculating the average for the batteries it is about 60mA, i.e. rather high.

Testing the mains transformer with 2500 volt and 5000 volt between mains and low volt side, did not show any safety problems.



Conclusion

This charger works best with batteries used in pairs, i.e. if all you equipment uses two or four batteries. I do not like chargers with that limitation, I prefer models that can handle each cell individually.
The specified time is fine for charging two batteries, but not for four!
The charger is good at terminating correct, but the trickle charge is on the high side. The low rate on usb means it can be used with just about any usb charger around, but it requires a lot of time to charge 4 cells.
The charger has a fairly high discharge current if battery are left in a unpowered charger.

If you always uses cells in pair it is a acceptable charger, if not stay away.



Notes

Here is an explanation on how I did the above charge curves: How do I test a charger