Curiosity - DC to DC step up converter in Baofeng 5RM battery

[Omega-TI]

Has anyone opened up the battery used in the Baofeng 5RM battery (the one with a USB C charging port)? When it's fully charged it reads 8.4 volts, but since you can charge it with a 5 volt source, I'm assuming they are employing a DC to DC step up converter in the battery. I'm curious what the circuit they are using is, but I don't want to destroy a new battery in the process of satisfying that curiosity. So if anyone has opened one up for whatever reason, a photo of the charging module would be interesting.

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[mc48]

3.7v per cell x two cells=7.4v as stated on battery.

 

[Omega-TI]

3.7v per cell x two cells=7.4v as stated on battery.

Yes, I know it's 8.4 volts, but the electromotive force of 5 volts could not by itself charge a battery to 8.4 volts, so I'm curious about the step up converter in the battery. If no converter is used, they must be charging the batteries in a parallel arrangement and using some sort of isolation between the two? Either way the batteries that supply the radio are in series.

 

[K4EET]

Hi @Omega-TI,

Have you used a voltmeter to actual read the voltage on a fully charged battery? The 8.4 VDC specified on the battery is a “Charging Limit” and probably not the voltage on a fully charged battery.

73, Dave K4EET

 

[Omega-TI]

Hi @Omega-TI,

Have you used a voltmeter to actual read the voltage on a fully charged battery? The 8.4 VDC specified on the battery is a “Charging Limit” and probably not the voltage on a fully charged battery.

73, Dave K4EET

No, I didn't pull the DMM out of the closet to verify it that way because when it's fully charged and you turn on the radio it tells you 8.4v. As you use it and it goes down, you can turn it off and back on and it'll read a lower voltage. So I'm "assuming" it's fairly accurate.

 

[AB4BF]

No, I didn't pull the DMM out of the closet to verify it that way because when it's fully charged and you turn on the radio it tells you 8.4v. As you use it and it goes down, you can turn it off and back on and it'll read a lower voltage. So I'm "assuming" it's fairly accurate.

You may have to find a "Travel Adapter" like I have. Some have 3 voltage outputs which seem to be intuitive and the one I have in my hand is a Samsung which outputs 2 voltages. Both 5.0 VDC at 2.0 amps or 9.0 VDC at 1.67 amps; all off of 120 VAC. It would definitely work on your 8.4 VDC battery. The 2 voltages cube came with my Samsung phone and the 3 voltages cube I picked up at Ollies. HTH!

 

[Omega-TI]

I don't know what to say, I apparently have not been clear enough in my posts.
I will say that, yes my drop in charger works fine.
The USB charge port works fine.
The voltage level appears fine.

All I am interested in is the charging circuit/method that allows an 8.4 charge level from a 5v input.

 

[FKimble]

It is probably charging each battery individually. Hot off charger the batteries will measure approx 4.2 vdc. Times two = 8.4.

Frank

 

[prcguy]

It is probably charging each battery individually. Hot off charger the batteries will measure approx 4.2 vdc. Times two = 8.4.

Frank

It can't be doing that with diode isolation and the only way would be with an internal switching supply. It could have two isolated switching supplies each feeding a single cell but more likely a single switching supply feeding both cells in series.

You could tear a battery apart and look for the switching supply to prove this or maybe probe the battery contacts with an oscilloscope and look for some high frequency ripple when the USB cable is attached. I would expect a measurable amount of ripple in the 20-40KHz range from a switching charger.

 

[slicerwizard]

Hi @Omega-TI,

Have you used a voltmeter to actual read the voltage on a fully charged battery? The 8.4 VDC specified on the battery is a “Charging Limit” and probably not the voltage on a fully charged battery.

73, Dave K4EET

8.4V is the series voltage of two fully charged lithium ion cells. The nominal/average voltage is lower. Lithium ion cells have a wide voltage swing between fully charged and fully discharged.

 

[prcguy]

8.4V is the series voltage of two fully charged lithium ion cells. The nominal/average voltage is lower. Lithium ion cells have a wide voltage swing between fully charged and fully discharged.

The question still remains, how do they charge a nominal 7.4v battery that reaches 8.4v at full charge with just 5v?

 

[slicerwizard]

I'm sure that most of us assume that there is a small DC-DC converter circuit in there.

 

[prcguy]

I'm sure that most of us assume that there is a small DC-DC converter circuit in there.

But we need to know for sure, some of us are loosing sleep over this.

 

[slicerwizard]

"Loosing"?

 

[mmckenna]

For Pete's sake, it's $18, someone buy one and crack it open!

https://www.amazon.com/BAOFENG-UV-5G-Plus-2500mAh-Battery/dp/B0CLXQYZV7

 

[prcguy]

"Loosing"?

See what lack of sleeep does?

 

[KevinC]

For Pete's sake, it's $18, someone buy one and crack it open!

https://www.amazon.com/BAOFENG-UV-5G-Plus-2500mAh-Battery/dp/B0CLXQYZV7

It states do not remove plastic covering or disassemble...

 

[prcguy]

It states do not remove plastic covering or disassemble...

View attachment 173147

Guess that saves me from wasting $18. Would it be local or Chinese police that would enforce this?

 

[Omega-TI]

It states do not remove plastic covering or disassemble...

View attachment 173147

... but it's not a mattress, it does not say, "Under penalty of law".

 

[prcguy]

... but it's not a mattress, it does not say, "Under penalty of law".

Great! So buy one, tear it apart and lets get a good nights sleep.

Edit: Uhh, that would be you in your house and me in mine. What were you people thinking????