Teardown: Tomo V8-4 / Soshine E3 USB Power Bank

Is it the official website for tomo powerbank ?
http://www.tomopowerbank.com

Hi Voung,
I have bought the TOMO M3. SHOP - TOMO
It is a very nice little charger and Iā€™ve added it to my laptop case. Iā€™ve had a problem with some other ones that have broken apart easily because I tend to put all my gadgets to some abuse tests apparently. This unit has lasted a couple of months already with no signs of damage, despite being dropped and otherwise misused. Itā€™s also the one that I stick in my shirt pocket when going through the airport because it fits so well and is just the right shape.
They send me 10% OFF coupe (FRIEND10) for next purchase, you can use the discount code if it is your first purchase.

Hi all! I just received my Soshine e3 (aka TOMO v8) from GearBest, gonna try it out with 4 Samsung icr18650 28A unprotected cells. These babys have to be charged up to 4.3v to get 2,800mah but at 4.2v they max out at 24xxmah. So! I should be looking at a combined rating of 9,600mah, so im expecting to fully charge my phone at least 2 full times (3,140mah battery). But weā€™ll see.

I have both a TOMO V8 & Soshine E3, at present they are both full of Panasonic 3500 mah NCR 18650Bā€s so potentially 14,000 mah each power bank :slight_smile:

Very nice! I have a few Panasonic mh12210 rated at 2,900mah, i might try those later on.

I mainly use my power banks when away in my camper van if we donā€t have a 240v electrical hook up where we are.
Each power bank will fully charge up my wifeā€s tablet from about 15-20% charge (she likes to run it down) 3 times or our mobile phones about 5 times each.

My longest cells fit in v8-4
Redilast protected 3400

Interesting powerbank, has anyone tested the efficiency of the Tomo V3?

Well, i got some strange results with my unit. The termination voltages are not precise at all and the Amp output is not accurate either (at least not the 2A slot).

Slot 1= 4.18v
Slot 2= 4.23v
Slot 3= 4.19v
Slot 3= 4.21v

Since i am going to be using this thing on a daily basis iā€™m gonna use my Samsung 28A cells simply because those can be safely charged to 4.3v.

I connected my LG G Pad 8.3 (which requires 2.8A to charge) to the 1A slot and all it did was connect and disconnect continuously.
The 2A slot only supplied 1.30A which is not enough to charge it.

As you guys can see, my unitā€™s lcd displays output current and voltage info. Not sure if all the models do this.
I connected my LG G Pro to the 2A slot and it charges without a problem, however the current draw shows 1.38A~1.44A.

Also, the longest cell i have is the Nitecore NL189 3400mah, at 70mm itā€™s a tight fit but it still works.

I do not normally charge cells in either my TOMO V8 or Soshine E3 preferring to use one of my analysing chargers instead.
However when I first got both power banks I did try charging cells in them.
I can remember that I checked the cells voltages with a DMM immediately after charging & all cells showed 4.19V.
Remember that the prescribed charging voltage for standard Li-ions is at 4.20v +/- .05v so that is 4.15v - 4.25v.
How did you test termination & cell voltage ?
I also tested the output of both units with a KCX-017 in-line tester whilst charging various items (phones, tablets & USB battery chargers).
I got readings from the power banks up to .98A when charging depleted items from the 1A outlet & up to 1.98A from the 2A outlet.
The KCX consistently shows readings 0.04A lower than the power banks themselves.
I do not know whether the power banks readouts or the testers reading are the more accurate (or the difference could just be due to the cabling between the power bank & item being charged & the in-line tester must take a few maā€s itself to run ).
I basically found that both charging & output were acceptable on both of my power banks.
I have just taken a couple of pictures of my TOMO charging my phone with the in-line tester in place & will put them up in a few minutes.

Hi there bella-headlight!
Well, as far as charging the cells goes, itā€™s just more practical (for me anyway) to charge them in the power bank itself rather than taking them out to charge and put them back in etc.
I dont have any fancy testing equipment, as soon as it reached full charge i immediately proceded to check each cellā€™s voltage with a multimeter.
I know there are certain tolerances to the max~min voltage on a Li-ion but since im carrying this thing in a backpack iā€™d rather use cells that can take the higher charge safely.
As for the Amp draw, i have absolutely no idea why my numbers are so weird. I did try different usb cables of various lengths but ALL of the showed even less Amperage at the outputs than the one supplied.

Still waiting for the pics to upload to my computer :frowning:
Not an insult but how accurate is your DMM ?
A DMM deviation of just 0.01% will give a reading of between 4.16v - 4.24v, depending on whether the deviation is high or low, on a true reading of 4.2v.

Accuracy? Lol whatā€™s that? Hahaha.
My dmm is a Sun pro brick from who knows when. I understand your point about the smallest deviation percentage causing some funky readings. But in my dmmā€™s case i think itā€™s not that of, my nitecore intellicharger i2 always leaves my cells at 4.2v (according to the dmm anyway) but cells charged with my xtar vc2 show 4.17v~4.19v. So who knows.

Yes we are talking about extremely small percentages here.
I use an Amprobe DMM which is supposed to be pretty accurate but who knows ?
I will probably get slaughtered for saying this but as your highest cell voltage reading is only 4.23v if it were me I would not worry & be happy charging & using normal 4.20v Li-Ions in the power bank.
At 4.23v, if that is really what the cells are at after charging, I would say that the worst thing that would happen is that you would lose a few life cycles from the cell.
That is only my opinion though & I am not suggesting that that is what you do as only you can decide what you feel is safe.

Hey no worries! I understand what you mean, but for all intents and purposes iā€™m gonna stick with the 4.3v cells, just to be on the safe side.

That is absolutely your decision to make, & the right decision for you :slight_smile:
I suppose a plus of doing that is that you will get good life cycles out of the 4.30v cells as they will always be slightly under charged :wink:

Thatā€™s right, at 4.2v my Xtar vc2 is showing a mAh capacity of 2,4xx as opposed to the full 2,800mAh when charged at 4.3v.
But thatā€™s fine since my smartphone has a 3,140mAh battery i could charge it at least 2.80~3 times. Or charge 2 18650 cells (2,900mAh) with my Xtar vc2 since it only uses 500mAh per channel. So in my case at least, it works as i need it to work.
Talk to you later mate, iā€™m of to bed! :smiley:

ā€œTalk to you later mate, iā€™m of to bed! Big Smileā€
No worries, I forget the time differences with where members on here live.
It is 12.30 noon here :slight_smile:

I got the 2 slots version (V8-2).

The charger voltage limits in my unit are 4.217 and 4.223 V, luckily very well inside the 1% margin. The curves are very good. The charging current is 400mA, and I will modify it to be 700mA (a resistor changed for each channel). So the charging section is pretty good.

When unused there is some drain from the batteries totaling 1.6 mA with peaks of 2.8 mA every second, the average is about 2 mA. This excessive drain can be eliminated inserting a switch to suspend power to the uC and converter. Anyway, it should only be a problem if batteries are left inside for weeks without charge.

The output is common to both ports, and can deliver in theory up to 2.1A total, it can not deliver 2+1A. Both ports are connected in parallel as one 2.1A, only the current sensing is separate for each port.

The uC senses the current of each port and shut downs the converter (always both ports) when any exceeds its firmware set arbitrary rating, as both are actually the same. I did not check the current limits for each port nor if the uC checks the sum to be below 2.1A for the maximum combined output. I verified that the 2A port can deliver 1.5A, good for most or all standard BC devices, and the 1A good only for devices known to draw 1A or less.

The charger port identification resistors are set for the proprietary, non standard, Apple approach, and are the same for both ports as 1A ports (which does tot match the 2A port label). I think the reason to identify both as 1A for Apple devices is to achieve compatibility with standard BC1.2 devices, although it is not the standard way to do it (it should be a short between D+ and D-, but the chosen Apple 1A setting should work with most or all BC devices too). For BC devices, it would mean that they can draw up to 1.5A, and thatā€™s why we see up to about 1.4A with most devices, and why these devices (those that can draw more than 1A) do not work well with the port marked as 1A, as they do not know about the 1A limit. In theory, it could deliver 2A total but only Apple or uncommon devices would draw 2A, and Apples will not because the port identifies as 1A per the Apple spec.

The drop in d4ā€¦d7 diodes causes the converter to stop working with battery voltage below about 3.5V, and to have an overall efficiency below 75. With better shotky diodes it could go down to 3.25V and about 80 efficiency, but only with smart bypass diodes will go down to 3.0V to exploit the full battery capacity and increase efficiency up to 85%. There are not smart bypass diodes similar packaging as the SS32, but i think they could be mounted anyway.
The converter is designed to work with single cell without bypass diode, but here it is used with bypass diodes, thatā€™s the reason for the abnormally high shutdown voltage and efficiency losses.

Overall, as charger the product is very decent. As power bank, not so much, but could be improved easily to be pretty good only changing the diodes, and placing a switch to avoid the excessive drain when unused.

Hope that helps.

I had the same issue with the v8-4.
It powers off already at <3.5V

Exchanging the U5 IC, a LDO which provides the PIC Mcu a constant 2,5V Voltage out of the 18650 Cells, helped. (see schematics here: http://shrani.si/f/G/13l/41eFUNyj/soshine-e3.jpg)

The original one had a far to big dropout of 1V. It already shuts down at <3.5V
The new LDO MCP 1700T-2502E has just a drop out voltage of 178mV. It cost me 60 Cents.

In theory it could down to 2,7V but since there is a shotkey diode in front of the LDO it breaks down at around 3.0V, exactly what I wanted.

But after all Iā€™m very disappointed of this powerbank.