Hello,
I am super new to electronics and working on a project where I want to connect a USB port to my Ebike battery.
My battery is 36V and 10 amp and I want to connect a USB port to charge my phone on the battery.
I have a step down converter to get the voltage to 5V but what about the amp's can it fry devices I connect, I think I am missing a componant.

Thanks for the help!

 

A voltage source, such as a battery, supplies the current required by the load, according to Ohms law. It does NOT supply the maximum available current to a load unless the load requires it.

 

that is all you need to step down DC voltage.
one thing to keep in mind is that 36V is rather high for device that only tolerates up to 40V.
That voltage will become higher during charging voltage for example....

 

Yes, indeed 40V is not enough for the input rating of the buck converter.
Look for a buck converter with at least 50V max input rating. There are some Recom 3 terminal regs with 72V input tollerance. You need to allow for volts rising during battery charging as "panic mode" says. Also an electric bike will have a lot of tranzients on the power supply so a tranzorb on the regulator input will be a good idea.

 

Hello,

As @panic mode said, the 40 Volts limit may be short during charging.
Perhaps a version of the DC-DC converter using a LM2596HV might be a better idea:
https://www.ebay.com/itm/DC-DC-LM25...786332?hash=item419895289c:g:6bkAAOSwpDdVE7pZ
That has a upper limit of 56 Volts.

Bertus

 

Wow, Thanks so much for the responses!
@panic mode @bertus @dendad

I ordered this step-down converter. So if i set the output voltage to 5V I can connect a USB port to the other side and it should work?
Is this the only component that I need? or is there another?



Thanks again, Your responses really helped me out!
P.s. Is there a smaller version of these buck down converters? Like a version that smaller so its easier to fit in my battery casing?

 

I ordered this step-down converter.

WOW! THAT'S A LOT OF REGULATION DOWNWARD. Consider how many amps (or milliamps) your cell phone is going to draw. You're going to have to dissipate a lot of heat through that LM317 regulator. Lets assume you're only going to use 200 mA (and that may be a lot, maybe not). Lets also assume you're max voltage during operation is going to be 40 volts. You're going to have to drop 35 volts. 35 (volts) X 0.2 (amps) = 7 watts. That doesn't sound like a lot, but it is. That's 7 watts of energy you're going to be converting into heat energy. If you put this in an enclosed container it's going to build a lot of heat. Eventually it will fry.

A buck converter (BC) is a far better choice. Since I'm not real familiar with how BC's work I can't say for sure, but I believe they work on a similar principal to how PWM (Pulse Width Modulation) works. They're on for a moment and off for a moment. Depending on how long they are turned on and how long they're turned off you get an average voltage. If it's on 10% of the time and off 90% of the time (and they operate on a relatively high frequency) you get 1/10th of the total voltage giving you an average voltage. In your case, 10% of 40 volts is 4 volts (average).

The device you ordered is cheap for a reason. It isn't likely going to suit your needs. Like I said, if your cell phone draws 200 mA to charge, that's an additional (5x0.2=1) one watt, bringing your total dissipation to 8 watts. AND given that this is not a perfect world, there's going to be other draws on it as well. Wire does not conduct 100%. a 100% conductor is called a super conductor. So there's going to be even more losses. And your battery voltage (on your bike) is going to waste energy and drain the battery faster.

[edit] It's interesting they are calling this "REGULATOR" a "BUCK - STEP DOWN CONVERTER". It's just a regulator. Does not operate the way a buck converter does. At least not to my understanding.

[edit #2] https://en.wikipedia.org/wiki/Buck_converter

What you bought is a linear regulator.

 

Hello,

The step-down regulator shown in the link of post #6 will not work.
The LM317 is a linear regulator with a maximum working voltage of 40 volts.
The naming linear will tell you taht a lot of heat will be dissipated when current is drawn.

Better use the regulator I mentioned in post # 5.

Bertus

 

I've recently seen several instances of linear regulators described as "buck" or "step down" by Chinese vendors.

It is rather like "DIP" - many Chinese vendors use DIP to mean "through-hole."

 

Given how long it will take to charge the battery from a USB port wouldn't a dedicated charger make more sense in the long run?

 

I've recently seen several instances of linear regulators described as "buck" or "step down" by Chinese vendors.

Which describes any linear regulator, since they can't do "boost".

 

Thanks everyone so much for the answers!

@Tonyr1084 So is a buck converter good, will it overheat, what are the options?

@bertus so is the item in #5 a proper buck-converter? Will it overheat or last?

 

Hello,

A buck regulator has a switching circuit, that cuts the power in pieces and stores the pieces in an inductor to smoothen the output-voltage.
Read this wiki article for more info:
https://en.wikipedia.org/wiki/Buck_converter

As the switching happens very fast, hardly any heat will be generated.

Bertus

 

The term Buck Converter is generally referring to a switch mode supply that has a lower output voltage than the input. A Boost converter is the opposite. That reg you purchased is no what is normally called a buck converter. It is always a good idea to check the Chinese addverts as they are often misleading.
And yes, a Buck converter is what you need NOT a linear regulator that operates as a series variable resistor to waste the excess voltage as heat. A switch mode regulator is either on or off so wastes much less power. It switches very fast, usually some thousands of time a second and the switching is filtered out so the resulting output is a steady voltage, more or less.
For power supply basics, have a look through these pages. There is a section on linear regs and switch mode.
http://www.learnabout-electronics.org/PSU/psu10.php
Also, a switch mode supply is much more erricient.
If you want to have a reg to supply 5V from a 40V supply at 1Amp, a linear regulator will draw 1Amp from the 40V battery and drop 35V across it, so 1Amp at 35V = 35Watts of wasted heat.
A switch mode supply only draws the same power (plus a bit for losses that are in everything) from the battery as is supplied to the load, so output = 5V at 1Amp = 5 watts. You will save almost 35Watts for each amp if you so to a switch mode. And at 1 Amp out, the supply will warm, not "catch fire" as the linear one would want to.

I see Bertus beat me

 

Thank you all so much for all the answers!

 

As others have mentioned, what you need is a good buck converter. An LM... voltage regulator will get REALLY hot, and will get destroyed. I recommend these buck converters:

https://www.amazon.com/eBoot-LM2596...76&sr=8-1-spons&keywords=buck+converter&psc=1

They are rated for 40 volts on the input, but some people could even get away with 50 (not recommended!) - so it's good for your 36V drill battery. And, in addition, they are very efficient. They will save a lot of power and also not melt and/or start smoking. Plus, it is always good to have some extra for future projects.

 

As others have mentioned, what you need is a good buck converter. An LM... voltage regulator will get REALLY hot, and will get destroyed. I recommend these buck converters:

https://www.amazon.com/eBoot-LM2596...76&sr=8-1-spons&keywords=buck+converter&psc=1

They are rated for 40 volts on the input, but some people could even get away with 50 (not recommended!) - so it's good for your 36V drill battery. And, in addition, they are very efficient. They will save a lot of power and also not melt and/or start smoking. Plus, it is always good to have some extra for future projects.

I have tested these some years ago and they fry up well before 50V

Depends if your 36V battery really has 36V if it is lead the voltage can be upto 14V and usually settles close to 13V. Then you pretty much have 40V. Lithium battery cells in fact are not 3.7V but can have upto 4.2V when fully charged.

I would not use the modules even at 41V but 40.00 are OK.

 

Well, whatever regulator the OP decides to use they can always throw some zener diodes or a power resistor in series with the input to reduce the voltage and wattage.

I would suggest six 5.1 5 watt zeners using a "euro" style terminal strip to mount them. At 200mA that's 6 watts right there, and 30 volts to boot...

There are also other ways to "pre-regulate" as to reduce the wattage of the final regulator.

EDIT:
Ok, so 4.3 volts would be better...

 

complicated

https://www.ebay.com/itm/HRD-Conver...ch-Step-Down-Power-Module-N-B1I2/183070575075

this one is for upto 48V and low cost, you get 12V out. You need another converter for 5V though but they are low cost also

https://www.ebay.com/itm/DC-DC-8-60...lation-Step-down-Module-200W-15A/332552160640

this module is adjustable directly and good for upto 80v

https://www.ebay.com/itm/10A-DC-to-...r-120W-24-60V-36V-48V-to-12-DROK/222793445858

If you can afford it, this module is waterproof you get 12V out

https://www.ebay.com/itm/DC-DC-5V-3...own-Converter-Module-Car-Voltage/282227299303

this is lowcost converting directly from 36V

I dont like the idea using a 40V rated chip on a 36V battery, i have seen these chips latching up at less than 50V
So if you design circuits for aviation (air plane) you would never work so close on the margin, fully charged battery has more than 36v, then you get transients from the large motor well in excess of that, you dont know if theres transient absorver or not, and this transient absorver also may fail.

Of course you could, suppose you only charge when it is not moving, not starting, and the battery not totally full, it will actually work most likely for a long time. But its close to the margin of these ICs which often is 40V, they only need a few volts more to fail.

Theres LED voltmeters too for 100V you should put one in parallel the line from the battery, and a good quality switch, and check the voltage before turning on, dont start it when you charge.

You may laugh about all this but over the years i have scorched many voltage converter modules.

and theres USB pinboards too, finally, no need to make a pcb and solder the socket yourself.

 

So this one goes all the way up to 60V but the question is will it over heat?