4x parallel slots for 18650 with individual Schottkey diodes for mitigation of differing voltage levels and reverse polarity and
4x TP4057 charging chips
2x USB outputs (1A+2A) with independent current limits
I’ll be gearing up to do some testing. So far though I can confirm that it doesn’t overcharge cells, but my example may have problem with undercharing (~4.17V) in the two rightmost slots.
Comments and questions appreciated, whether here or on the site.
I wonder if there is anyone else on here with one of these. I did another test after a recharge cycle and again the two cells in the rightmost slots are undercharged at 4.16-4.17. I guess its within the 1% accuracy range claimed on the datasheet for the charger chips, still I wonder if anyone else is seeing the same behavior?
My USB XTAR MC1, along with others in the line, have a claimed /.05 termination accuracy; 4.175 4.225? Have you checked the 4 cell voltages after sitting for a couple of hours for any balancing action? My i4 charger has about.02 deviation between both banks for my sample. I do a quick check before 4 cells are put in service in SRK which balances the cells in short order.
I’m still trying to justify buying a battery bank. Driving and flying provide USB charging ports in most cases. I do some primitive camping where I would be more interested in light weight solar charger, which of course could be used with 4 cell battery bank to avoid multiple devices needed to be charged after hours.
Then again I’m in Katrina country where only natural gas for faithful Pramac Geny was available for 2 weeks. The power bank and all my charged laptop pulls could come in handy if nothing submerged, no?
I ended up going down the laptop-pull + DIY power bank rabbit hole in the first place because I was disappointed that the “Kmashi” 10,000 mAh hour pack I got from Amazon for $18 to keep in my bag was heavier than expected due to using 2,000 mAh cells. When I ordered the TOMO, I didn’t have any other way to charge Li-ion cells, but even now, its convenient to just recharge in the case.
Lateotter, thanks for linking to your report. I remembered some of those details, but I couldn’t remember where I’d seen them. With your report + mine it sounds like there is probably something inherent in the design and manufacture of this charger that causes undercharging in the two right-most channels, rather than just a simple random assortment of the variation between samples of the charging chip.
I’m also having some iOS device power negotiation issues with this, particularly when I put a USB meter in line. My iPad3 clearly manages to draws over 1A, but not as much as it does from the 2.1A Apple USB charger it came with. I haven’t been able to get it to deliver more than ~1.3A with a 10 Ohm USB resistor load.
Peak power draw I’ve seen while charging the batteries in the powerbank is ~1.5a or so.
I need to update the post with some other observations I’ve gathered.
I’m waiting for that bank, can’t find everywhere on internet the max length of 18650 that can be used with it, can you measure so I can order the batteries? Thanks!
I’ve made a number of updates in response to questions from readers since first publishing this review.
2014-08-27 Review section added with voltage/current measurements and overall impressions of product.
2014-08-31 Added max cell length
2014-12-04 Updated max current delivery upward to reflect the results of new tests with different testing equipment. Also added note about overheating cut-out with >2A total load.
2014-12-09 Updated to reflect that both ports use the Apple standard to signal that devices may draw up to 2A.
Hi Voung,
I have bought the TOMO M3. SHOP - TOMO
It is a very nice little charger and I’ve added it to my laptop case. I’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. It’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.
Thanks!