Test/review of Tomo Power bank M2

Yes, but it depends on how much current you draw from it.

Scary Ninja fast response! Thanks. Since most of us have more batteries than we know what to do with. The Power bank/battery charger is probably the best idea going. I really like the 2-4 cell line up from Tomo. Could you do more reviews of this style using loose cells?

Thanks again, Paul

I am also working on a 4 cell Tomo, but it will be some time before I publish that, I have a few other power bank reviews I need to publish first.

The two slots in this power bank are independent apparently. How does it handle two cells that have different voltages while charging or discharging to the USB output? In another power bank you tested it only charged/discharged one cell at a time and just switched between them. But this one doesn’t seem to have that behavior. Thanks.

Is it safe to use unprotected cells in it (LVP)? I’m guessing the answer is no if it draws 0.7mA from a battery at 1.9v

The power bank will stop discharge when the cell reaches ~3.2V, so it does have LVP. But you’re right there is still a small parasitic drain so you can’t leave cells in there and just forget about it for months. Most power banks have some parasitic drain.

It uses from the cell with highest voltage first and it is independent charge circuits for each cell.
In my review of M4 I do open it up and take a look at the circuit: Review of USB battery box Tomo M4

Depends. It will turn off output when the cells are discharged, but the standby drain will damage the cell if you leave it discharged for some time.

So it switches between the (balanced) cells quickly as they discharge? In your test with 2x18650 you measure the current and voltage of just one cell, and the curve looks very smooth.

Just bought one of these power banks along with a couple more Lii 100 chargers from gearbest.

Switches may be the wrong work, it opens up for the cells when the voltage is the same. Because I started with two full cells they where both uses simultaneous.

I think I understand now, thanks.

Just got my M2 powerbank. I’m satisfied with the overall apparent build quality. It seems to work fine. The cell capacity meter is a little odd/inaccurate. I measured the following:

5 bars: >3.87V
4 bars: 3.74V-3.87V
3 bars: 3.54V-3.74V
2 bars: —-
1 bar: 3.05V-3.54V
0 bars: <3.05V

I first was testing with a power supply with 0.1V resolution and it went right from 3 bars to 1 bar. I then made a voltage divider with an adjustable resistor to get finer resolution and I was still not able to get 2 bars. So, it roughly works; the 4 to 3 bar transition means you have approximately 50% left, and the 3 to 1 bar transition means you have approximately 25% capacity left (with a sanyo GA cell).

I just noticed a peculiarity. While the powerbank is outputting current a not-very-hard tap to the end with the ports causes a restart. This doesn’t happen when the powerbank is on but not outputting current.

This powerbank has reverse polarity protection as my daughter found out when she put in one of the batteries backwards and then tried to charge them. The one that was reversed showed as empty while the other one showed the correct charge state. However neither charged when connected to a USB charger which is a good thing in my opinion.

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4953 dual P-channel mosfet (FDS4953)
LM393 dual comparator
55b7 TP4055 1 cell charger (R3 & R4=2K 400mA charge ~40mA cutoff)
G5177C boost converter
9926 dual N-channel mosfet (FDS9926)
8205S dual N-channel mosfet (STT8205S)

I have the Tomo V8 and just leave the cells out of it until I need it.

I guess it works as intended.

Chris

What’s the difference between the M2 and the V8 - 2 ? Are they newer and older versions?
GearBest even has them at different prices, and the V8 is more expensive.
They appear similar though.

The V8 is discontinued.
Here’s some tear down:

I have a TOMO K2 coming someday. Looking to replace my XTAR PB2 which didn’t work out well.

….Looks like it made it here, to San Francisco ISC anyway

I”ve had a M2 for a month or so, put in good new cells, and it seems to work fine, BUT I notice the green back light is often on with nothing connected just sitting on the desk. A few seconds and it says poweroff and goes dark, but later I see it back on again…

That’s the V8-4. Apparently it’s an older version of the M4, also small difference in size. But, i’m talking about the V8-2, which could also be discontinued, but it’s still sold in a few places.