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Adafruit USB Li-Ion/LiPoly Charger - v1.2
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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Sun Feb 10, 2019 7:53 am

@Luke

I am not an expert on the product and may not be of much help there but since you are not sure where the problme is, have you tried the following:
Have you measured the current to the battery when it should be charging ?
Have to tested the voltage across the battery terminals before charging and after the battery is connected to the charger (with the charger connected to a supply voltage)?
Have you tried charging a similar battery and was it successful ?
If you have, please share the results.
Last edited by Alli on Wed Mar 27, 2019 2:06 am, edited 1 time in total.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by luke1976 on Sun Feb 10, 2019 6:05 pm

Thanks so much for your reply. I had not realised lipo batteries were so sensitive (if that's the right word). I hadn't charged it in over a year, and it may be that I simply can't charge it any more and I need to try again with a new battery. Although from memory, it never did charge the battery (which was new when the charger was new).

I will get my meter out and post the results.

Thanks again.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Fri Feb 15, 2019 9:52 am

@Mike

Is there a rule that states what the resistance should be in conjunction with the input impedance of the micro when measuring the supply voltage?

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Sat Feb 16, 2019 1:29 am

There's no specific rule for the resistor values, but 150k-150k is convenient.

When the LiPo voltage is 3.6V, the current through that voltage divider will be about 12uA. Current will always flow through those resistors, but it will take about 80 hours to consume 1mAh of energy stored in the LiPo.

If you dropped the resistor values to 150-150, the current through the divider would be around 12mA, which would drain a 1000mAh LiPo in about 80 hours.

Higher resistor values create larger errors when you read them with an ADC pin though. The pin draws a small amount of current from the divider to get its measurement, and that current creates an error voltage across the divider's resistors. The ADC current is around 1uA, and the current through a 150k-150k divider is about ten times larger than that. That keeps the errors small enough to safely ignore.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Sat Feb 16, 2019 9:51 am

Thanks again Mike. Truly grateful for all your advice and assistance

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by crazy1gadgets on Sat Feb 23, 2019 7:22 pm

Can this device be configured to charge a cell phone? Based on various articles I have read I have heard it is not always best to charge cell phones to 100% maximum, so I am trying to control charging rate so that I can limit the overnight maximum charge the cell phone receives (I usually plug in at night, and unplug 1st thing in the AM). So far I have not had luck. I have made my own JST to USB-Micro adaptor to plug into the cell phone and I get no indication the phone is charging at all. Any comments on this would be welcome

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Mon Feb 25, 2019 3:13 am

No, the phone has its own, built-in LiPo charger that wants a 5V DC power source.

Charging to 100% is okay as long as you don't leave the LiPo sitting that way for a long time (more than a week or so). The preferred level for long-term storage is 80%.

LiPos aren't subject to what's known as 'memory effect' in NiCads, so charging back to 100% is okay even if you haven't drained the LiPo all the way.

The LiPo charging cycle is kind of complicated, so LiPo chargers are careful not to overcharge a cell, or to start a new charging cycle when it could put unnecessary stress on the polymer.

If you want to exercise your phone's LiPo more (let its charge drop lower before recharging), you can do it by charging every other day, or just checking the battery level before plugging in the charger. If the battery level is higher than about 75%, you can skip that night's charge.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by crazy1gadgets on Fri Mar 22, 2019 2:37 pm

Thanks, this helps a lot!

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Sat Mar 23, 2019 9:59 am

Alli wrote:tested the resistor used in the case of the USB charger from adafruit to be 2kohms which means the charge current is 200mA. Now under the section where is specifies the current level before charge termination occurs, what will that threshold current

Mike wrote:For the version of the MCP73833 we use, it would be 5% of 200mA, or 10mA.


Hello @Mike, just want to clarify, since the PROG resistor is 2kohms, which means the charge current is a maximum of 200mA, does this also mean that the maximum current drawn by the load can only be 200mA ? Or is the limit of the charge current of no consequence since the load is fed from the battery in this case?

Also if the charger controller's input pins were plugged into a 5V supply whilst it is still connected to the load then in that case will the current supplied to charge the batter plus the current drawn by the load be limited to 200mA from the charger controllers supply? i.e. Will the total current supplied by the charger controller to both charge the battery and feed the load be 200mA so that if the load required more than 200mA the load would supplement this excess current from the battery?

Thanks in advance.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Tue Mar 26, 2019 10:54 pm

Alli wrote: just want to clarify, since the PROG resistor is 2kohms, which means the charge current is a maximum of 200mA, does this also mean that the maximum current drawn by the load can only be 200mA ?

No. 200mA is just the maximum amount of current the charger sends into the LiPo while charging it.

Alli wrote:Or is the limit of the charge current of no consequence since the load is fed from the battery in this case?

That's correct.

Alli wrote:Also if the charger controller's input pins were plugged into a 5V supply whilst it is still connected to the load then in that case will the current supplied to charge the batter plus the current drawn by the load be limited to 200mA from the charger controllers supply?

That's also a no.

If the load current is greater than 200mA, the LiPo will supply the rest. Under those conditions, the LiPo will discharge even while you have the charger plugged in and running.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Wed Mar 27, 2019 2:08 am

Great, thanks for clarifying @Mike.

I also wanted clarity on the following: The datasheet states that each pin has ESD protection and the device has
6.1.1.4 Reverse-Blocking Protection
The MCP73833/4 provides protection from a faulted or
shorted input. Without the protection, a faulted or
shorted input would discharge the battery pack through
the body diode of the internal pass transistor.

pg20

If i understand this correctly, does this mean that if any circuitry connected to the load causes a short (If the load shorts), the battery will be protected from the short circuit current?

Does the charger controller protect the load and battery from current spikes if the current supplied spikes (surges) on the DC - and DC+ terminals of the charger controller?

Is it necessary to implement a fuse to protect both the charger controller and the battery and load ?

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Wed Mar 27, 2019 5:11 am

Alli wrote:If i understand this correctly, does this mean that if any circuitry connected to the load causes a short (If the load shorts), the battery will be protected from the short circuit current?

Not quite. That says the LiPo is protected from shorts between the MCP73833's VDD pins and GND.. the power supply to the LiPo charger, not the load connected to the LiPo.

Alli wrote:Does the charger controller protect the load and battery from current spikes if the current supplied spikes (surges) on the DC - and DC+ terminals of the charger controller?

Yes. That's the "Supply Ripple Attenuation" (or PSRR) value in the table of Electrical Characteristics.

In the datasheet I have, the MCP73833 has 58db of attenuation (about 800:1) for supply noise up to 1kHz. It has 47db of attenuation (about 225:1) for signals up to 10kHz, and 25db of attenuation (17:1) for signals up to 1MHz.

Alli wrote:Is it necessary to implement a fuse to protect both the charger controller and the battery and load ?

Fuses protect power supplies from short-circuited loads.

In the event of a shorted load, the fuse keeps the power supply's positive terminal from being connected to GND. Instead, all the voltage between the power supply's output and GND falls across the fuse. Assuming a 3.7V supply and a 1A fuse whose internal resistance is 0.1 Ohm, a short to GND would be enough to pull 37A from the power supply. Instead, the fuse will blow when the voltage across it gets significantly higher than 100mV (1A through 0.1 Ohm). The fuse element is designed to fail quickly and completely before the shorted load can damage the LiPo.

There are fast-blow fuses that protect sensitive components from sudden bursts of current, but those are iffy in practice. You have to get a pulse of current large enough to melt the fuse element and hope the fuse blows before any of the pulse reaches the protected component.

To protect loads from their power supplies, you want either a voltage regulator or a Transient Voltage Suppressor (TVS) diode in parallel with the load.

TVS diodes are made from particles that act like diodes when they touch each other. For a TVS operating within its safe working range, there are so many diodes in series that the TVS looks like an open circuit. If the voltage gets high enough, the series diodes start to conduct, pulling current away from the load.

The current flowing through a TVS heats the particles up and makes them expand. The expansion causes more particles to touch each other, creating more paths to GND in parallel with the first one. The heat generated by current flowing through the TVS temporarily welds together, particles that touch each other lowering the resistance to current either way.

Most of the particles that got welded together will break apart again as the TVS cools down, so TVS diodes are self-healing after the surge that shut them off in the first place. Not all of the particles come apart, so the TVS degrades over time if you trip them repeatedly.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Wed Mar 27, 2019 5:36 am

Okay thanks @Mike. I will look into that.

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by Alli on Tue Apr 02, 2019 5:13 pm

@Mike

Mike, if my input voltage is 5Vdc to the DC+ and DC- terminals of the charger of the charger controller what will VREG be? the datasheet on page 3 says that VDD (Im guessing is the 5Vdc input) will have a minimum voltage of Vreg+0.3 but also on page 3 it says that VREG has a range of voltages from 4.2 to 4.5 which is determined by VDD=Vreg+1V. NOw i have measured the input DC voltage to be 5.5V so Vreg should be typically 4.5V? If this is correct then what happens if i apply 6 volts to DC inputs?

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Re: Adafruit USB Li-Ion/LiPoly Charger - v1.2

by adafruit_support_mike on Wed Apr 03, 2019 2:06 am

Alli wrote:if my input voltage is 5Vdc to the DC+ and DC- terminals of the charger of the charger controller what will VREG be?

VREG will be whatever is set for that particular MCP7833. There are versions that use 4.2V, 4.35V, 4.4V, and 4.5V, each made for a specific LiPo chemistry.

We happen to use the 4.2V version, since that's the full-charge voltage for the LiPos we carry.

Alli wrote:the datasheet on page 3 says that VDD (Im guessing is the 5Vdc input) will have a minimum voltage of Vreg+0.3

That appears in the 'Minimum' column. It means VDD has to be at least 0.3V higher than VREG for the charge cycle to finish.

Alli wrote:it says that VREG has a range of voltages from 4.2 to 4.5 which is determined by VDD=Vreg+1V.

That's in the 'Conditions' column, which lists details they used while measuring that value for the datasheet. The exact condition is:

VDD=[VREG(Typ)+1V]

which means "we measured VREG using a VDD value 1V higher than the value in the Typical column for each variant of the chip." For a 4.2V MCP7383, they used VDD=5.2V, for instance.

Alli wrote:NOw i have measured the input DC voltage to be 5.5V so Vreg should be typically 4.5V?

No, it doesn't work the other way around. The value is VREG is built into the chip, and you need to choose a value of VDD to match it. Changing VDD doesn't have any effect on VREG, but if VDD is too low, the charger won't work as expected.

Alli wrote:what happens if i apply 6 volts to DC inputs?

The charger will work and VREG will be unchanged, but you'll be right on the edge of "don't blame us if the chip dies under those conditions" territory. An unexpected voltage spike could kill the chip.

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