3.7 to 5v ?

If you have an old auxiliary backup battery for a cell phone there is a circuit inside that takes the 3.7 volts of the battery and boosts it to 5 volts. This circuit will also allow you to charge the 3.7 Lithium battery with a standard phone charger. The only catch is that it may require a certain level of output current to remain on. In other words the 5 V device that you want to power with the battery might have to draw 20 or more mA to keep the circuit engaged.

John

Again, the device calls for "5V 1A". So if it requires "1A" and I have 11.1v - 3.5a and I step it down, or I have 3.7 with 10.5a with a step up, wouldnt that work ? 

Hi OT

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.

If you want to build a converter yourself there are some integrated circuits available that allow you to build a converter by adding the correct resistors, capacitors, and inductors. Unless you have a good back ground in electronics it might be a fairly steep learning curve as a first project.

I want to make a clarification as I get the impression from your question that you may think that the battery or power supply decides the amount of current that it will supply to the device. The battery or converter has an internal resistance and provides a voltage. The device also has a resistance. When the voltage of the battery is put on the device a current flows through the resistance of the battery and through the resistance of the device. This current is equal to the Voltage of the battery divided by the added resistance of the battery and the device and is measured in Amps. I could have a 5 volt battery as big as a house and I would get the same 1 amp current when I hooked up your device that I would get if I hooked it up to a much smaller 5 Volt battery. For this reason batteries do not come with an amperage listed on them. What you may see however is an Amp Hour or milli-Amp hour rating. These ratings give us some idea how much power is in the battery. The device that we put on the battery will determine how much current in amps flow in the circuit and if we divide that measure of Amps into the Amp Hour rating of the battery we get a rough idea of how long the battery will run the device before it runs out of power.

If I have missed your question you will have to rephrase it and try again.

John

I have reread your original question and I will add this. There is the same amount of energy in 3 batteries in parallel as there are in 3 batteries in series. If you had a 100% efficient switch mode converter to use in either case the device would run the same amount of time with the parallel as it does with the series configuration. For this to be true a switch mode converter would be required. There is also a buck converters called linear regulators which will also take 11.1 volts and change it to 5 volts. The linear regulators do not however do this efficiently and you would loose over 1/2 of your batteries energy to heat and your time of operation would likewise be cut in half. The linear converter will not work to boost from 3.7 Volts to 5 Volts.

John

John,  I understand the difference from Series and Parallel.   But as for the "Switch mode converter" ? Like the one in the attached photo ?  I'm only pointing out the component itself. Not the entire board. I found this on Sparkfun. This is a breadboard part. 

Or could I modify this part, insulate the bottom then just plug in my 3 series batts into  this and switch to 5v output ? I think this this entire board requires a 6 v input.

I'm not apposed to building my own pcb but I'll need a  schematic to print out if that's available online some where. As long as it has all the correct parts listed I need to install. I'd have problem with the calculations but it they already done then no problem for me

to build it.

But isn't this part already made and available ?

Oscar

https://www.sparkfun.com/products/15868

Attachments:

Hi Oscar,

If you want to use the batteries in parallel here is a boost converter on ebay, They are selling 5 of them plus shipping for half the cost of the Spark Fun module.

https://www.ebay.com/itm/6pcs-MT3608-DC-2A-Step-Up-Power-Booster-Module-2v-24v-Boost-Converter-Arduino-US/201897905217?hash=item2f020d8c41:g:JiwAAOSwjIRZkczl

Or if you want to use your batteries in series here is a buck converter that will allow you to reduce the 11 volts down to 5 Volts. this one even has a volt meter built into it.

https://www.ebay.com/itm/XL4015-5A-DC-Buck-Step-down-Adjustable-Voltage-Power-Converter-w-LED-Voltmeter/142968844998?_trkparms=ispr%3D1&hash=item21499b72c6:g:y8IAAOSwKAFdyOi2&amdata=enc%3AAQAFAAACcBaobrjLl8XobRIiIML1V4Imu%252Fn%252BzU5L90Z278x5ickk7d4nremBkvNKtcC0ZwqXDKxWjUbeS%252Brt4FDOu9xDC5GHYQTkvK0ElkeC7w1HV7cIUu2lJM%252Ft5mheSMoPyFW9S2mYvtGuX4InhtIc0ySelZElXaGukUolN12tTFBil7XlKnsd7mH%252B2Dr4E6%252BFyaNIuHz71FqLFC5IggfAWNQre8HyPLHZrJI6nb0UUxjvyJMescCkJmz%252BbRANTmrO56Oa4DRR7SCqo8CfBPEuj8WgR31CLyqNf%252FcDEBbkBcxpLO7xnQpDyCDRyMPR3VjlWlQtRZb0txIkSW4oLxEGSMmaSl5RMQYvf5eufX9s4QDXQ2JOv6Boe4if7blmkNQd69QdDIHxIzuaG%252BkGO2VwybShfxiUHzbDJeYP2QzjNvKrI2uosf3QWNYX7%252FKQspJD6R4TsHVhgkMX3XWXaxnC2FSaTrrrcLRaXs%252F9V7k2qp%252FNYGG%252BCtTyishz6pISgGZ0AzMwmiD8xa1KnEbMqIu%252BBh%252BTnimnIvYkY4VxxOmzye9qXg6vdM%252Bobp6gf%252FyRj3c%252Bfwry48zzQayvFcRIulPdzxcqPNsKbug9frhTp73PJ0WIhgHBVc7My%252F0ashWf9gYT%252BsBjRbHR3ZPuHYM2%252BsaOa%252B6LI4RiipBRfpT3JKTwRi1w0H01lHwiNPqMPAFPqyN%252B24%252BaGVHtwZCZCSDz9HrLLDLa1LhrpIhJlvJeTEr3w5fTJDuJnO4P9OPfOkqvIxM8B4hqfnsOceuwseFF8xka5jtr3b6ySQJMn49Tb%252BxyHIFpfbUMi%252BwqbPh8OxEmtDWsD5efrw%253D%253D%7Ccksum%3A142968844998a5ccf24819204b5e86cd2c0112057f5c%7Campid%3APL_CLK%7Cclp%3A2334524

Here is a link to the images available of different DC to DC converters. Sometimes I get ideas for which chips to use in a circuit from looking at these image displays in Google.

https://www.google.com/search?sxsrf=ALeKk00j8uk5UlPIfNC-CtlmSqEOrBkDkg:1600269210356&source=univ&tbm=isch&q=DC+to+DC+boost+converter&sa=X&ved=2ahUKEwimzs-u--3rAhVPaM0KHUEWDwUQsAR6BAgCEAE&biw=1920&bih=933

If you see a module that you want to build you can note the number of the main control IC and then go to a supplier like Newark and find that IC in their stock. Click on the link to the ICs data sheet and many times the data sheet will supply a typical or recommended schematic for the design of a circuit for the IC.

John

Another source in a slimmer package and fixed voltage but along the same lines as what John suggested are these:

• https://www.adafruit.com/product/1385
• https://hobbyking.com/en_us/kingkong-5v-3a-ubec.html?queryID=937cf1b75f83b9f96f0daf3037fcb8c5&objectID=20575&indexName=h…

I note the second one isn't in stock but there are others.  You may be able to get something like this at a local hobby shop where RC aircraft and such are sold.  They are DC-DC switching buck converters so your batteries would have to be in series.

Another source in a slimmer package and fixed voltage but along the same lines as what John suggested are these:

• https://www.adafruit.com/product/1385
• https://hobbyking.com/en_us/kingkong-5v-3a-ubec.html?queryID=937cf1b75f83b9f96f0daf3037fcb8c5&objectID=20575&indexName=h…

I note the second one isn't in stock but there are others.  You may be able to get something like this at a local hobby shop where RC aircraft and such are sold.  They are DC-DC switching buck converters so your batteries would have to be in series.

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.