Problem running USB Proto Board off of LIPO battery
Ragtop
Posts: 406
I am trying to run a proto board off a 3.7v 2000mah Lipo battery but it does not seem to get enough juice to operate. The indicator light is dim and it will not make a serial connection to the PC.
Might it work if I bypassed the 5v regulator or am I just out of luck. Works fine when I plug the board into the wall outlet.
Might it work if I bypassed the 5v regulator or am I just out of luck. Works fine when I plug the board into the wall outlet.
Comments
You can patch your 3.7V in to the 5V pads on the board if you are sure that you will not apply external power at the same time - I don't think you want that 5V feeding into your battery. I'm assuming you are using a protected battery or know what you are doing since lipos can be interesting [1] if you abuse them.
This also assumes that the dropout on the 3.3V regulator is low enough that it will still work. If not, you may not be getting 3.3 V to the processor (that's pretty close and your battery may drop below the required level pretty quickly anyway).
If you connect the battery to the 5V pads, anything that is connecting to 5V will get 3.7V instead. After a quick look at the schematic, I think this is limited to the PS/2, VGA, and servo (if you connect them to 5V) headers.
There has been some discussion recently about whether it is safe to apply a voltage to the output of the regulator (which you would be doing here) but you should probably be ok.
There are also boost regulators out there that will bump your 3.7 V to 5V (or higher for that matter) if you require 5V. This may be a better way to go and will probably get you better performance since the battery level is likely to drop below the regulator's cutoff pretty quickly.
[1] interesting = really, really dangerous.
The proto board is set-up as a GPS datalogger and I was hoping the rechargeable Lipo's would be cheaper then eating through 9Vs. I was planning
on changing out the batteries for charging instead of trying to charge the batteries on-board.
It has three 3.3V devices: the propeller chip, GPS, and SD card writer.
It's funny you mention that. I just got one of the ones with the 5V boost circuit.
I haven't used it in an application yet. I have used it to charge a battery once. It was a nightmare to unplug the battery afterward - even using tools. Some of these plug/jack pairs are extremely tight.
One thing to bear in mind for anyone interested in these is that they do not have any way to turn them off. The battery is always connected to the boost circuit. This is fine for a device that is supposed to be on all the time but inconvenient if it's not.
Sparkfun and Pololu (and I'm sure many others) both sell small boards with boost circuits on them if you need the 5V.
That's what I was talking about (unclearly) in my first post above. The 5V pads next to the regulators are connected to the input of the 3.3V regulator.
That's my plan. I just forgot to do it before plugging in the battery the first time.
AA NiMh are easier to use and safer. 4XAA are ok if you feed the 3.3V regulator, otherwise use 6xAA.
Massimo
Wiring the Lipo's power to the left pin of the 3.3v reg and ground to the middle ground pin did nothing. No indicator light came on. I am bypassing the switch but turned it on and off for good measure. Wondering if all those "back" circuits might be a problem.
I may just have to bite the bullet and build my own prop board for this with just a 3.3v reg.
Couldn't agree more, folks implementing these types of batteries really need to be careful and become thoroughly informed about the hazards(fire, rupture, battery longevity) before using them. Only use them with protection PCBs that protect against over charging, over discharging and short circuit conditions. If placing two cells in series use a mult-cell type protection PCB rather than two separate single cell PCBs. Li-ion cells have characteristics that are desirable (great Coulomb efficiency in both charge and discharge, awesome self discharge and outstanding energy density) and are worth the extra trouble.
To use a single cell for your application you could either use a boost converter (as schill recommended) to bump the voltage up to the specified minimum for the board or bypass both regulators and use a low dropout regulator. Some specialized linear regulators have dropouts below 100 mV, so you can harness most of the battery's capacity.
I think the problem now is because, for the regulator on the board, the input voltage is not high enough. 3.7V is not much more than 3.3V (obviously) so unless the regulator has really low drop out this will not work.
Instead of wiring the battery directly to the 3.3V regulator, did you try just connecting to the 5V holes on the board? It should be exactly the same thing electrically. I don't think (although I don't know for sure) that you are running into problems because of the 5V regulator.
I think the best bet is to use something specifically designed for this situation as suggested by Miner_with_a_PIC - either a regulator with very low dropout or a boost/buck converter to get to either 5V or 3.3V, depending on whether you need the 5V.
I will probably go with the low drop-out reg. Another wait by the mailbox.
I have some 3.3V zener diodes, someone mentioned running it through a diode.
What is the consensus on that approach?
Running lipo's in series is fine, as long as the packs have the same capacity and are charged to the same level. You can't charge them in series without a very specific charger that connects to both cells and keeps them in sync. My remote control stuff is all lipo powered, and all with 3 cells wired series for ~12v.
No. If you look at the schematic you can see that 5V ties directly to the input of the 3.3V regulator. It's just an easy way to make the connection.
The only way to buypass the power circuit completely would be to tie directly to one of the 3.3V holes. But then you'd be driving the Prop directly with the battery voltage which could be as high as 4.2V (I believe) and is outside the normal range for the Prop.
If you come up with your own regulation that provides 3.3V, you can connect that to one of the 3.3V holes. This will provide power to the rest of the board. It will also be going to the output of the 3.3V regulator but that should not be a problem. If you are concerned (and some people think you should be) then you can remove the 3.3V regulator from the board completely or disconnect its output pin.
The sparkfun charger will not be able to do this. You would have to charge them individually and then hope everything was good.
Shawn
Try the LDO (Low-dropout regulator) rated for 3.3 Volts - that could fix the problems: most wouldn't care if there's a 12V car battery at the input - it will regulate it to 3.3 Volts (as well, it will just quit working at 3.42 volts - thing to check for drop-out voltage in the datasheet!)
Or, you can try use the 2.7 - 9 volts to 3.3 Volts DC-DC converter (Texas Instruments have such kits if you can find it).
And, yes, you can try PMIC - some do have 3.3 V voltage regulator / charge pump which is already powerful enough to power the Propeller and few other things, as far as the inductor's current rating goes.
I just have to use the advanced Li-ion battery protector chip from Maxim Semiconductors, Inc. to protect the battery (although you would have to work a bit more for 3.2 Volts Li:FePO4 batteries - even spinel Li-Ion batteries are safe providing you don't leave it short-circuited for too long - although the MOSFET will just give up magic smokes and then dies totally open - 18650 batteries are pretty powerful, it can do 40 Amps short-circuit peak - did this risky test a long times and I was pretty surprised).
NiMH or Li-Ion, it doesn't matter as long as it's just the plain vanilla-favored 3.3 volts. (What comes in won't matter - many voltage regulators and DC-DC converters just take care of voltage conversion. Also, some LDOs provides the protections to Li-Ion batteries automatically (when it drops to 3.42V, it shuts down, and when shorted from 3.3V output, it also shuts down) - I still put in the battery protector chip anyways, as some can die short-circuited. I like to be on the safe side. I never have had any trouble with canned Li-Ion batteries like 18650 ever since.)