This is a placeholder topic for “Polymer Lithium Ion Battery - 3.7V 2400mAh” comments.
What’s the connector on this battery? Is it JST? Which series?
Hey David, the connector on all of our Polymer Lithium batteries is a standard 2-Pin JST-PH (2.54mm) Connector.
Is this suitable for the MKR 1500 NB? Does it have a female 2 pin JST PHR2 Type connector?
Hey Andrew,
Welcome back to the forum!
The JST connector on the MKR 1500 NB is compatible with our 2-pin 3.7V LiPo batteries. JST-PH connectors are designed to “lock in” to the appropriate sockets to maintain proper continuity, so just a word of warning you may find the connection to be a little snug if you try to remove it from the socket after plugging it in.
And for the charging rate, is it correct to say 0.5C = 1.2A for this 2.4AH battery?
And that the ideal charging rate is 1.2A at 4.2V?
Would it tolerate a 5V/0.5A wall charger?
Can it be connected to microcontroller and charger at the same time? Can you recommend an appropriate connector please?
Hi Andrew, welcome back!!
A 0.5C charge rate ought to be right 
When charging a battery they are usually done in a few stages, some with a current source and others with voltage source. A dedicated IC usually handles this like the:
A 5V/0.5A charger will definitely damage the battery and likely cause a fire.
To connect to a microcontroller at the same time I’d go for a product like the Amigo Pro:
And a PH-PH cable to extend that connection:
Here’s a resource that goes through the basics on charging: A Guide to Understanding LiPo Batteries — Roger's Hobby Center
If you have any more questions let us know!
Liam
Thanks for your reply.
I’ve been doing a bit more research and it seems, given my project is a battery-powered Arduino-controlled irrigation system which could be subject to high summer temperatures on my balcony, that maybe a NiMH battery would be a safer option. Would you agree?
I’m thinking 6 or 8 AA cells in series to drive the pump (5-12V) and a tap of at 3 or 4 cells to drive the MC (3.3V). Ideally I’d link to be able to charge and operate the system simultaneously.
Is there a charging circuit you can recommend for this application?
NiMH Cells are not self-balancing, so tapping off several cells in series is not recommended. It can be done, but caution is required, especially if temperature might be an issue. You might be thinking of lead acid cells, which are self balancing and which are often used with a tap for light loads such as the 12V cab radio in a 24V truck system. For your setup it would be preferable to use a converter to generate the 3.3V for the MCU.
Apart from the voltage requirement for the pump you need to consider whether the batteries can meet the load. While NiMH batteries have a low internal resistance and can deliver a good level of current, lithium batteries are generally rated for very high current. If your pump is a very high current device, or requires a high current to start, then NiMH might not be adequate for the task.
Ah ok, I was unsure about tapping off at a lower voltage with the NiMH batteries - good to know!
I’m currently using a ESP8266 12F board which has a Vin regulator (upto 10V >> 3.3V) so i guess I should just use that? I have had this running with 2x 9V rechargeable Li-on batteries (Enegon 1Ah) but it didn’t last more than about 4-5 days so was trying to go for a longer duration option. My thinking regarding the tap for the MC, was that Vin regulator would be wasting current when feeding it 9V.
The pump (SKU: FIT0200, DFROBOT) I have is from Core Electronics. 4.5-12V / 0.5-5W which at 9V input should draw no more than ~0.5A and I’m guessing ~1.5A at inrush. If i’m using six or eight 2Ah batteries (AA NiMH) in-series then I’m thinking this should be ok? Does this sound right? I think I could also limit the inrush by PWM control on startup if recommended.
Another option would be separate supplies which would reduce the loss from the regulator and would also eliminate any risk of spikes being fed back into the MCU from the motor start/stop. For best battery life you can arrange for a device that powers up the MCU at intervals to check if the motor needs to run, but whether or not that is practical depends on your use case, and is getting complicated.
NiMH is well suited to a permanent trickle charge setup, but they do get hot when operated like this and might be damaged in a hot environment.
However I am not sure about your calculation. When you are comparing the options you need to compare wattage, not Ah. Six 2Ah 1.5V batteries is the same power as two 1Ah 9V batteries.
Hi Andrew
Heed Jeff’s warning here. I will add DO NOT tap off ANY type of series battery string for a lower voltage. You just MIGHT get away with it using LiPos which have a battery management system to balance out charging currents but still not good or recommended practice.
As a cell charges and the voltage increases the required current will decrease. Now if you have say 2 cells in series and one of them is depleted more than the other the charging current is the same through both cells. As the higher charged cell requires less current this means that this reduced current is all that is available for the lower charged cell and it will never fully charge. If you have a series string in a radio, camera etc the probability is that all cells will discharge pretty equally so charging such a string will be ok. BUT if you ever have to replace any cell(s) in such a string good practise is to replace ALL of them with cells of a like charge. Tapping off some cells for a lower voltage will gradually deplete the maximum charge these cells can accept with lowering voltage and ultimate failure of the whole string.
And for Jeff as well
This is NOT the case. Lead acid cells will self balanced if connected in parallel but if connected in series will behave pretty much as above. I know it used to be a practice particularly if the 24V was 2 12V batteries in series but there is not much mention on how often the batteries were replaced.
In summary. DON’T do it with any series combination of cells.
Also take note of Jeff’s last statement
Six 2Ah i.5V cells is 9V @ 2Ah. NOT 12Ah. Once again the same current flows through ALL the cells resulting in the same total Ah figure as 1 cell.
Cheers Bob
Lead acid cells self balance quite satisfactorily, provided the tapped load is small which is the example I quoted. The difference in charge level is no greater than the inherent difference of charging rates between cells due to differences in the electrolyte. If the load is occurring when the battery is not being charged then the fully charged cells will gas slightly but that is rectified with regular maintenance that lead acid requires in any case. It has been done for years on trucks and boats with no impact on battery life, or at least no impact that can be identified separately from all the other factors that affect lead acid cells.
From what I can tell, the Pimoroni would not be a good choice to connect to a ESP8266 12F as I would still have to connect via the on-board voltage regulator (Vin) beacuse of the 4.2V output of the Pimoroni which I think woudl be too high for the MCU. I’m trying to avoid the Vin pin to save power.
The Makerverse option above looks to be a better option as I could power the MCU straight from the 3.3V output. Is this correct? I’m just wanting to be certain as you did mention the Pimoroni as being the better option for connecting battery and device simultaneously.
The Makerverse board should be able to power the MCU using the 3.3V out. Just need to keep in mind that it is limited to 200 mA output.
The Pimoroni can function more like a UPS so you can connect power and power the device and charge the battery at the same time.
Thansk Aaron,
From what I can find, ESP8266 draws upto 350mA so i guess the Pimoroni will be the best option but this now presents my next problem → the 4.2V output is too high for the MCU (3.6V max). Doing some reading here: How to power the 3.3V ESP32 from a 3.7V Li-ion battery? - ESP32 Forum
I’m thinking about one of these two options:
TPS62136 data sheet, product information and support | TI.com
High Current, Low Power, LDO Regulator XC6203 - Torex Europe
I still need to read up on these but any advice here would be much appreciated.
Hi Andrew,
Good catch on the mA specification for that Pimoroni board. From my understanding you could get around this shortcoming by using the 5v out from either charger Liam recommended connected to a 3.3v voltage regulator such as this one.
The 200mA limitation seems to be only for the 3.3v output so you could probably get around fairly cheaply using a regulator like that.
Let me know if this helps!
Sam
Thanks Sam - I think I’ll need the Pimoroni as the Makeverse 5V supply is only available when powered by USB → I need to provide 3.3V supply to the MCU from a 3.7V LiPo via a regulator.
For the regulator, the one you recommended isn’t much better than the ESP8266 onboard regulator at ~5mA quiescent current versus 8uA for the XC6203.
Cheers Andrew
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