Maybe I can't read this correctly, but what is max current output to load here?

https://www.ti.com/lit/ds/symlink/b...https%3A%2F%2Fwww.ti.com%2Flit%2Fgpn%2Fbq2003

 

This Chip doesn't control the "maximum" Current,
that's supposed to be done by You,
based on the Ratings of the Battery You are Charging.
It can reduce the maximum-Current via PWM, but not "set" the maximum-Current.

Why do You think You need such a sophisticated Charger ?
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This Chip doesn't control the "maximum" Current,
that's supposed to be done by You,
based on the Ratings of the Battery You are Charging.
It can reduce the maximum-Current via PWM, but not "set" the maximum-Current.

If I understand you correctly, I_out max === battery I_out max?

Why do You think You need such a sophisticated Charger ?

Fundamentally I am trying to build a "pass through" system that will maintain load voltage and current independent of external power connection, capable of charging the battery even while power is being drawn. So;

External power connected, battery full - load is powered externally

External power connected, battery partially charged - power is divided between battery charging and load, but still meets specific load requirements with some safety factor.

External power disconnected - battery engaged, meets same load requirements as previous case

Thanks so much

Joe

 

Why do You think You need such a sophisticated Charger ?

We sure have a plethora of confrontational responses here.

"Why do You think You need...." could easily be stated as "An easier way of doing this might be....." Maybe people have a reason for a complicated approach, or maybe they just want to do it a certain way. Or quite possibly, they don't know there's an easier way to accomplish what they are trying to do and will welcome the suggestion. But don't put people on the defensive and make them justify what they are doing with a condescending almost hostile question.

 

We sure have a plethora of confrontational responses here.

"Why do You think You need...." could easily be stated as "An easier way of doing this might be....." Maybe people have a reason for a complicated approach, or maybe they just want to do it a certain way. Or quite possibly, they don't know there's an easier way to accomplish what they are trying to do and will welcome the suggestion. But don't put people on the defensive and make them justify what they are doing with a condescending almost hostile question.

*shrug* I appreciate the support but I'm not particularly offended.

 

You can't do both at the same time,
and still gain from all the sophisticated features of this Chip.

The Chip can not perform all of it's functions while
connected to a Battery AND a Load at the same time.

You will need to set things up in an automatic "switch-over" fashion, just like a UPS.

But do You really want to use Nickel-Cadmium or Nickel-Metal-Hydride Batteries ?.....
Why ?
The Power-Density is substantially higher in Li-Ion Batteries,
that's why they are so popular.

You can easily accomplish this with Li-Ion Batteries as long as your project will run properly
on exactly these Voltages ........ 4-Volts, 8-Volts, 12-Volts, or 16-Volts.

You can, of course, regulate any of these Voltages down to suit the application,
but Voltage-Regulators will always affect Battery-Run-Time in a negative way.

The "Rules" and Specifications are different for each type of Battery.
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*shrug* I appreciate the support but I'm not particularly offended.

You can't do both at the same time,
and still gain from all the sophisticated features of this Chip.

The Chip can not perform all of it's functions while
connected to a Battery AND a Load at the same time.

You will need to set things up in an automatic "switch-over" fashion, just like a UPS.

But do You really want to use Nickel-Cadmium or Nickel-Metal-Hydride Batteries ?.....
Why ?
The Power-Density is substantially higher in Li-Ion Batteries,
that's why they are so popular.

You can easily accomplish this with Li-Ion Batteries as long as your project will run properly
on exactly these Voltages ........ 4-Volts, 8-Volts, 12-Volts, or 16-Volts.

You can, of course, regulate any of these Voltages down to suit the application,
but Voltage-Regulators will always affect Battery-Run-Time in a negative way.

The "Rules" and Specifications are different for each type of Battery.
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.
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My mistake, I missed the part where it was specifically for NiCad/NiMH.

I have seen a number of ICs that promise exactly this sort of "UPS" behavior. I have the datasheets in my downloads, and can give you a list if you need. Perhaps you have one you might recommend?

 

I like to build my own stuff, just for entertainment.

Are You interested in building your own ?,
or do You want it microscopic sized ?,
or a pre-made Module(s) ?

What is the exact Voltage and Current-Capacity that You need ?
How much space do You have to work with ?
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I need 6A, 4V DC out. Actually 5.5 V 3.5A but I'm adding a safety margin. I don't care if it's an IC or separate parts, whatever is cheaper. As I mentioned my primary concern is that the load does not "detect" external power disconnect.

Would be nice if I could use both single cell and multiple cell, as well as both LiIon and LiPo. Bit that's frosting.

 

OK,
At least 24-Watts.
How long do You expect this Battery / UPS setup to Power your Electronics after AC-Power is lost ?

This a tremendous amount of Current for a 5.5-Volt Battery Supply,
You must be Powering something else other than a simple Micro-Controller, ( or similar ).
Don't keep us in the dark !, the details may well be very important.

Do You have a budget in mind ?, ( both in Dollars, and in Space ).
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OK,
At least 24-Watts.
How long do You expect this Battery / UPS setup to Power your Electronics after AC-Power is lost ?

This a tremendous amount of Current for a 5.5-Volt Battery Supply,
You must be Powering something else other than a simple Micro-Controller, ( or similar ).
Don't keep us in the dark !, the details may well be very important.

Do You have a budget in mind ?, ( both in Dollars, and in Space ).
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Batteries - I have 4 18650 cells, be nice to use them

Space - the total system volume is 1in by 7 in by 13in. It's a little less than half occupied right now

Cost - as low as possible. $50 is really pushing it.

This is for a Raspberry Pi with screen.

 

Got it ........
A Raspberry-Pi, even with a display, is not ever likely to require more than about 1-Amp.

Does your Board have an on-board Voltage Regulator ?
What is it's minimum input-Voltage for proper Regulation ?
This is required information.

I'm assuming that it actually requires 3.3-Volts for normal operation, is this correct ?

Are there any other connected Peripherals that must have more than 3.3-Volts ?
If so, exact Voltage and Current-Specifications are required.

Have You measured the actual worst-case Current requirements of your complete setup ?
This is required information.

How long must the Battery keep everything alive ?

Is an "Alarm-Output" of some sort required before
the Battery is automatically switched Off to prevent Battery damage ?
If so,
will it be just an LED ?, an LED and a Buzzer ?, or
maybe an external signal to some other device for an "Orderly-Shut-Down" ?
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A Raspberry-Pi, even with a display, is not ever likely to require more than about 1-Amp.

A Pi by itself, no. A Pi with all USB ports loaded, yes . My specs are directly from RPi documentation, which specifies _minimum_ 2.5A supply for Pi 4b alone.

Does your Board have an on-board Voltage Regulator ?
What is it's minimum input-Voltage for proper Regulation ?
This is required information.

I'll have to get back to you on that. I can easily give graphical schematic (_not_ circuit diagram) of the boards. Whether everything is labeled sufficiently for what you're asking I've no idea.

I'm assuming that it actually requires 3.3-Volts for normal operation, is this correct ?

No. 5 volts _minimum_. for the Pi alone. Inline USB power meter (between PSU and Pi PCB) reported 5.1V load.

Have You measured the actual worst-case Current requirements of your complete setup ?
This is required information.

This is... a tactical problem. Assuming even I was able to document exhaustively everything I currently own that I may or may not want to connect to the Pi, there is absolutely no guarantee that tomorrow I may not get something different. My hope (perhaps unreasonably optimistic) is that there is some design robust enough to withstand any possible existing load given enough batteries.

I realize this is a difficult problem. My distinct impression is that even the people who made my laptop didn't solve it.

ETA: Sorry, clicked 'post' accidentally

How long must the Battery keep everything alive ?

I would say at least 2 hours, the longer the better. Again, I'm hoping for a solution that will allow me to simply add cells if I don't like the battery life.

Is an "Alarm-Output" of some sort required before
the Battery is automatically switched Off to prevent Battery damage ?

That would indeed be very helpful. RPi has GPIO pins that can measure some voltage, we can simply take one or two of those and tell the OS to shut down when it detects some value.

Thanks so much for all your time. Even what you've asked so far in terms of fleshing out the problem, is extremely helpful as an alternative to buying random ICs and potentially destroying them.

 

How many is "all" USB-Ports ?, ( @ 1-Amp each ).
Is this a single USB-Port that comes already installed on the board ?,
or are You adding additional USB-Ports ?

The "2.5-Amps" rating probably includes 1-Amp for the built-in USB-Port.

"Just adding more Batteries" creates a huge amount of complications with
insuring that the Batteries are equally Charged, and Loaded.

With a ~5-Amp Load for ~2-Hours, requires a battery with at least ~12-Amp/Hours of capacity,
there's no practical way to run ~20- 18650 Batteries on the same Charger and with the same Load.
This is why I said the actual numbers are very important in making the necessary calculations / decisions.

With a ~5-Amp Load for ~2-Hours, we're getting into the range of
a "large 6-Volt Gel-Cell-Battery" (SLA, Sealed-Lead-Acid),
or maybe a Custom "Hobby-Grade" ( RC-Drone) Li-Po Battery for a cool ~$200.oo+.

You would need 2 similar to this Battery, in parallel, (~$64.oo pair ) ...........
https://www.batterymart.com/p-6-volt-6-5-ah-sealed-lead-acid-battery.html

Actually, using 2 of these SLA Batteries would be the easiest and cheapest solution.
1 of them will last roughly ~1-Hour @ ~5-Amps.
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How many is "all" USB-Ports ?, ( @ 1-Amp each ).
Is this a single USB-Port that comes already installed on the board ?,

There are 4 USB ports on the board, 2 USB 3.0 and 2 USB 2.0. It would be nice to power all of them, but I'll settle for one USB3 and one USB2.

Of course, I may end up with a powered USB hub that I'd like to draw power from the same supply. But if that's off the table I'll skip it.

Actually, using 2 of these SLA Batteries would be the easiest and cheapest solution.
1 of them will last roughly ~1-Hour @ ~5-Amps.

I guess I was misled by the fact that existing UPS systems use 4 18650 cells. I guess they're intended for extremely brief interruptions.

I know enough about SLA to be nervous about carrying them on my person. How about these? They seem to be the right form factor too.



OTOH these things have been known to explode too. So maybe my concerns about SLA are misguided.

You've put in so much work on this I'm starting to feel uncomfortable not paying you. At the very least, I'll reach out to RPi foundation to see if they will let me put their logo on the finished product and/or sell it with them. If there's this much work involved then it follows it's worth investigating as a commercial product

 

This is not "work", it's either entertainment, or just a time killer.
The only work in these Forums is trying to dig information out of people,
sometimes you'd think that they're working on a top secret government project.

The USB-Ports don't require a specific amount of Current to operate,
but what gets plugged into them could add-up to a substantial amount of Current,
especially the relatively new USB 3.0 Ports.

The Battery that you've posted is far from ideal.
You will loose around ~20% of the Battery's capacity in the "Voltage-step-down-process", possibly more.
The Battery Voltage needs to be as close as possible to the required Voltage to reduce losses,
so the 6-Volt SLA is just about ideal, and a "2-S" Li-Po Battery, ( with only 2-Cells ),
will come in at around 7.6-Volts, which would also work reasonably well for what You need.

Just keep in mind that You need a "2-S" ( ~8-Volt ), Li-Po Battery
rated for at least 6,000 mAh to get 1-hour of run time.
That's 6-Amps for 1-hour, ( if you're lucky ).

There's no need to worry about either of the Batteries being particularly "Dangerous",
but either style MUST HAVE substantial protection against physical-damage, or being dropped.

A "Hobby-Grade" Li-Po is the easiest to build a Circuit for because they can usually be
comfortably Charged at up to ~"5-C", ( some are even higher ), ( this is 5X the mAh rating ),
in the case of a 6Ah Li-Po that would be as much as 30-Amps of Charging Current,
and it would be completely Charged in about ~15-minutes,

( but don't believe the 50-C rating on the Battery in the Picture, this will seriously reduce Life-Expectancy,
this is an all too typical Chinese BS rating, there are "legit" Batteries, made in the USA, but You will pay ),
( Max-Amps.com for custom American-made Li-Po Batteries, with real performance and longevity ),

therefore You don't have to worry too much about limiting the Charging-Current of a Li-Po
like You would with the SLA Battery.
This also means that the Li-Po will accept a Charge much faster than the SLA Battery.
Easily twice as fast, but consider the fact that it will take a huge AC Power-Supply to accomplish that feat,
and super-fast-Charging REQUIRES WATCHING THE BATTERY as it charges, the whole time !!!
A 1-C or 2-C Charge Rate is generally completely safe, and doesn't require any special attention.
Potentially excessive Temperature build-up is the issue with super-fast Charging.
The quality of Battery-Construction is usually the determining factor.
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super-fast-Charging REQUIRES WATCHING THE BATTERY as it charges

I have to run off and do other stuff, so I'll get to the rest of your points a bit later. But, there is no requirement for "super fast charging" of any sort here. Either the system is connected to power and being used, or it's connected to external power and "sleeping", or it's disconnected from external power and being used. 2/3 of the time it's connected to external power. More like 80% of the time.

But, if I felt like it, couldn't I simply monitor temp buildup with a sensor?

Again, thanks so much for your help. Tomorrow I will start reaching out to electronics suppliers and I will have a much clearer idea of requirements thanks to our discussion.

 

And yeah, that max amps site is waaaaay out of budget. I may need to reconsider the lead acid situation. My other problem is they're much heavier obvs.

 

It's maxamps.com btw

 

From what I can tell by the datasheet, LTC4412 is my best controller option. However, datasheet specifies up to 6 LiIon cells in series. Thoughts?