Hohm Tech School2

DSC_2432

DSC_2433 DSC_2434

A two slot LiIon only charger from Hohm Tech that is USB powered.

DSC_2419 DSC_2420 DSC_2421 DSC_2422

The charger was in a cardboard box with specifications on it.

DSC_2427

The box included the charger, a USB cable and a instruction sheet.
The USB cable is very thick.

DSC_2435

The charger has a USB micro input.

DSC_2436

There are no buttons, only a led for each slot. The leds is red while charging and green when the battery is full.

DSC_2442

There is two current settings on the charger and they are selected by the battery length. There is a nice marking showing at what point the current changes.

DSC_2443

The charger has specifications on the back.

DSC_2439 DSC_2440

The connection are the common slider style that can handle from 32mm to 76mm, this means all batteries will fit.

supportedBatteryTypes

supportedBatterySizes DSC_2509 DSC_2510 DSC_2511
DSC_2512 DSC_2513 DSC_2514 DSC_2515 DSC_2516

The current for 10440 is a bit on the high side.



Measurements charger

HOHM%20School2%20%28SA18650-33%29%20%231

The charger uses a sort of CC/CV charging, but the current drops in fairly large steps. This is not a problem for the battery, but will mean slightly longer charger time.The charge time is not that long, because the charger maintain full current up to about full battery voltage, before it is reduced. Termination current is around 160mA, this is a slight high for some batteries.

HOHM%20School2%20%28SA18650-33%29%20%232

Second slot is similar, but the final voltage is slightly different.

HOHM%20School2%20%28SA18650-26%29%20%231
HOHM%20School2%20%28PA18650-31%29%20%231

These two batteries are similar.

HOHM%20School2%20%28BE18650-26%29%20%231

The regulation has some problems with this cell, but the end result is good enough.

HOHM%20School2%20%28KP14500-08%29%20%231

The smaller battery means lower charge current.

HOHM%20School2%200%2C5ohm%20%28SA18650-33%29%20%231

Simulating a weak charger or long cable with a 0.5ohm resistor do not prevent the charger from charging the cell, but the termination is not that good.

HOHM%20School2%20%282xSA18650-33%29

With two cells at 1A it cannot maintain full current as long, this means slightly longer charge time, but the end result is fine.

Temp7567

M1: 40.6C, M2: 41.1C, M3: 44.8C, HS1: 53.3C

Temp7568

M1: 57.0C, M2: 45.4C

PowerOnLiIon

The charger needs about 8 seconds to reach full current.

Unpowered%20voltage%20sweep

The charger will discharge a full LiIon battery with about 0.22mA.

Voltage%20sweep%200-4.25V%200.5A
Voltage%20sweep%200-4.25V%201A

The charge profile. The drop in charge current is probably heat related, the charger use a linear regulator and when the LiIon battery is at low voltage the regulator will get hotter.

Charge%20Solar%20LiIon

The charger will not work with a unstable voltage.



Conclusion

It is a simple and easy to use LiIon charger that does what it is supposed to do.

I will rate it as fairly good.




Notes

The charger was supplied by a Hohm for review.

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