3.7 to 5v ?

Sorry I wasn't very clear on this. If you pull up the last link to a page of Google pictures of converters I only meant that if you look closely in some of the picture you will be able to identify the part number of the main IC that is being used. If you then do a search and find the data sheet for that particular IC they often have suggestions for circuits with schematics and recommended parts on the data sheet.

John

Frank, isn't the second part your recommend for LiPo Batteries only ?

There isn't any information on the second part linked but in general a BEC is RC lingo for voltage regulator.  2S-6S LiPo is the way they are designating the allowed voltage input but a voltage regulator doesn't really care where the voltage comes from as long as it is in spec.  Where battery chemistry and perhaps packaging would be important is where there is also a charging circuit which this does not have.

The Adafruit product is also a BEC but has information on the regulator used.  It is a MP2307.  Reading the datasheet it is apparent it is just a buck regulator.

Your question is a good one.  If uncomfortable, look for additional information like Adafruit gives or one of the other recommendations here.

I agree with the boost converter scenario. Using the batteries in parallel implies self balancing and that could help with their life cycle, also you can upgrade to more batteries to achieve longer capacity or less batteries to achieve a more compact design.

That is a good question. If your device is designed to run on 5 Volts and it draws 1 Amp yes you can obtain this from either a step up converter (called a boost converter) or from a step down converter (called a buck converter). I will assume 100% efficiency for these conversions. In the case of the 3.7 volt boost conversion the converter will draw 1.35 Amps from the 3.7 volt battery in order to deliver the 1 Amp at 5 Volts. If the efficiency is less that 100% AND IT ALWAYS IS the current draw from the 3.7 volt battery will be more than 1.35 Amps. In the case of the 11.1 Volts and a buck converter the converter will draw at least 0.45 Amps from the 11.1 Volt battery in order to deliver 1 Amp at 5 Volts. There are DC to Dc converters on sale on ebay that will allow you to do either of these conversions.

Hello John,

So would you say it would be better to go with a series circuit configuration for more efficiency and less heat ?

Oscar

Hi Oscar,

As long as you use a switch mode converter, whether the batteries are in series or parallel  it will both work about the same for heat loss. If you are going to try to charge the batteries in the unit the Parallel would have some advantage as mentioned by a previous poster. Otherwise it is your choice and may also depend on whether you find a buck or a boost converter that you like.

John

Hello John,

I ordered the boost converter and I'm waiting for it to show up. But I have another question concerning a different device: if I have a larger capacity batt with the same voltage output as the device requires, do I necessarily need a protection board of any kind between the batt and the device ?  Thank you, Oscar.

Hi Oscar,

This is a great question.

There are two main dangers involved with Lithium Batteries. #1 is over charging them and #2 is allowing them to discharge below a certain point. These two conditions can damage the batteries permanently and in some cases cause them to overheat and catch fire. We have all seen the videos of devices exploding into fire. That is the purpose of the battery protection devices. They know when the battery charge is getting too low and they disconnect the battery from the load or they sense when the battery is fully charged and they stop more charge from going into the battery.

Now if you have a way for the your device to stop working before the battery gets too low and if you are removing the batteries to charge them on an approved charger then you probably do not need the protection circuit. I for example use lithium batteries in many of the LED flashlights that I have around the house. When the light beam from the flash light starts to get weak I remove the batteries from the flash light and put them into a special Lithium battery charge that has its own battery protection circuit and recharge them. I do not have separate protection circuits for these flashlight batteries.

We all like to use the Lithium batteries because they have what is called high density energy storage. Lots of energy in a small and light package. Unfortunately the side effect is the danger that all this energy presents if something goes wrong. Since the lithium battery is fussy about how it is charged and its intolerance of being fully discharged, battery protection circuits are important. All devices that use a lithium battery have the protection circuits built right into the battery packs.

Another way that protection circuits help the charging of lithium batteries is the situation where we want to charge two or more lithium batteries that are in series. Here the problem is called a balancing problem. If the batteries are not perfectly matched one battery may get more of the charge than the other. This is caused by a difference in the internal resistance of the batteries. This allows the charger to put a higher voltage across one battery than across another. Ultimately this damages the batteries and can cause failure of the battery pack. The protection circuit can sense the condition of each battery and treat each one as if it is the only battery that is being charged.

If you see the protection circuit as a way to protect the battery while it is being used and while it is being charged you will better be able to decide if a protection circuit is needed in your application.

John