Help with understanding voltages and currents

[leyla1989]

So I’ve been trying to self learn of Google for the past week but no straightforward info and loads of different websites are now making my head mashed ! ….. I’m trying to understand voltages and currents And how they add up differently in series as to parallel !

So if we can post an example please to help me
Use 7.4v and 5000mah. As an example

This is my guess

In series 7.4 v would give you = 14.8v and a 5000mah current

In parallel 7.4v would give you = 7.4v and 10,000 mah current

I think I’m prob wrong

If there’s any other factors in understanding how they are added up or useful diagram as Google is just confusing things more

Thank u leyla
This is for two 7.4v battery’s

 

[Greywolf74]

In series 7.4 v would give you = 14.8v and a 5000mah current

In parallel 7.4v would give you = 7.4v and 10,000 mah current

This is correct. Series always adds voltages together with same capacity and parallel is the exact opposite. Adds capacities together but voltage remains the same.

 

[bill_delong]

Yes, you're on the right track, but mAh is considered "capacity"... the current doesn't flow unless a draw occurs and depending on the power of the motor will be how much current is drained.

Another important factor is efficiency where I've posted some results of going from 2S to 4S on my SCT here:
https://www.teknoforums.com/threads/build-review-sct410-3.1389/post-14872

and here:
https://www.teknoforums.com/threads/build-review-sct410-3.1389/post-22242

Simply put, 4S (higher voltage) is more efficient and will offer close to double the run time when running nearly the same Watt Hours

 

[tudordewolf]

So I’ve been trying to self learn of Google for the past week but no straightforward info and loads of different websites are now making my head mashed ! ….. I’m trying to understand voltages and currents And how they add up differently in series as to parallel !

So if we can post an example please to help me
Use 7.4v and 5000mah. As an example

This is my guess

In series 7.4 v would give you = 14.8v and a 5000mah current

In parallel 7.4v would give you = 7.4v and 10,000 mah current

I think I’m prob wrong

If there’s any other factors in understanding how they are added up or useful diagram as Google is just confusing things more

Thank u leyla
This is for two 7.4v battery’s

Your math is generally correct, but I believe there may be an underlying misconception about "mah" and how current works. "mah" stands for milliamp-hours - it's a measure of capacity against time. Current is measured in Amps, abbreviated "A", and milliamps are 1/1000th of an amp.

Voltage is supplied by the source, like a certain amount of pressure being available from a tap. If you had a big kitchen faucet and a tiny bathroom faucet on the same water line, they would receive the same pressure, but the one with a greater "draw" would be the one that allows more water to flow.

Current is drawn by the load, based on its resistance, sort of like a large faucet allowing more water to flow through it. (and reactance, but for the sake of discussion we'll model it as entirely resistive)

The mah rating of a battery doesn't directly describe the amount of power it can supply, but rather how long it can supply power for. The C-rating describes the amount of current a battery is supposed to be able to supply (some manufacturers are known to exaggerate this value), as a multiple of the current capacity. A 10C battery can supply up to 10 times its "mah" value as current. That is, a 500mah 10C battery can provide up to 5 Amps (5000ma) of current.

If you draw too many amps from a battery, it usually damages them, either immediately or from the rapid buildup of heat that occurs with overcurrent conditions.

 

[leyla1989]

thank you …. Understanding how the charger works so 14.8v. With 5000 mah.

Charging ing at 5 amps but the voltage increases from 14.8v to 16.8v. But these are not amps. I don’t understNd how amps make volts. I’m missing something and getting confused

Amps is the flow rate into a big reservoir ?
So the 5 amps flow into a reservoir of 14.8v which make the reservoir bigger in size to 16.8v

But we’re do 5000 mah fit in all this ….. confused

 

[bill_delong]

thank you …. Understanding how the charger works so 14.8v. With 5000 mah.

Charging ing at 5 amps but the voltage increases from 14.8v to 16.8v. But these are not amps. I don’t understNd how amps make volts. I’m missing something and getting confused

Amps is the flow rate into a big reservoir ?
So the 5 amps flow into a reservoir of 14.8v which make the reservoir bigger in size to 16.8v

But we’re do 5000 mah fit in all this ….. confused

Yes, Amps is current and mAh is Capacity (stored current)

Voltage is just the fuel gauge telling how much capacity is filled into the pack

https://batteryuniversity.com/article/bu-903-how-to-measure-state-of-charge

 

[leyla1989]

I think something is twigging I just need to digest one of the posts correctly
Any one find a decent easy diagram of how amps flow and volts ?

 

[tudordewolf]

Wait a min ignore this last message I think something is twigging I just need to digest one of the posts correctly

I think the key is that "ma" and "mah" are measuring different things. The first is a flow rate, and the other is a sum over time.

As for the 14.8 / 16.8v thing - that's the "nominal" versus maximum voltage of the battery. It's why we often refer to systems as 2S or 3S (or more), because it gets confusing fast, especially at higher voltages, what someone might be referring to. Nominal means its the average voltage from full to empty; a lithium battery at 100% charge has a higher voltage than one at 30%.

A lithium battery has a nominal voltage of 3.7 volts, which is where 14.8 comes from (4x3.7), but a maximum voltage of 4.2v, which is where you get 16.8 from.

You'll set a low-voltage cutoff in your ESC of something like 3.1 volts per cell, which is 12.4V. Seeing the charger go from 12.4V to 16.8V just means it's charging it back up to full.

I think something is twigging I just need to digest one of the posts correctly
Any one find a decent easy diagram of how amps flow and volts ?

I think what you're missing is ohm's law

Let's use light-bulbs instead of motors for a second, and I need to introduce a third value, "resistance"

Voltage is abbreviated "V" (volts, easy)
Current is "I" (from "intensity")
Ohms are "R" (resistance)
Power is "W" (watts) - this is the true measure of energy flow; volts times amps

Imagine we're using a 6V battery, with 1000mah of capacity.

You hook up a lightbulb with 6 ohms of resistance.

Current = voltage divided by resistance ( I=V/R )

6 volts / 6 ohms = 1 amp.

Power = volts times amps (W = V*A)

6 volts * 1 amp = 6 watts.

The lightbulb will glow with 6 watts of power, and the battery will last 1 hour.

You recharge the battery, and hook up 2 lightbulbs in parallel. They both have 6 volts across them, so each draws 1 amp, for a total draw of 2 amps.
The battery is now supplying 12 watts of power, and only lasts half an hour. Each bulb glows as brightly as the single one did before.

You get a second battery and connect it in parallel to the first. Their voltage is still 6V. The brightness of the bulbs does not change. Now their combined capacity is 2000mah, and they can power the 2 bulbs for a whole hour. You remove one of the bulbs, and now they can power a single bulb for 2 hours.

You replace the lightbulb with a more powerful one - counter-intuitively, it has a lower resistance, 3 ohms. You hook it up to your 2 batteries in parallel. and it draws 2 amps of current (6 volts / 3 ohms = 2 amps) - it's drawing 12 watts of power, (6 volts times 2 amps), glowing twice as brightly as the original bulb. It'll drain the 2 batteries together in 1 hour, or a single battery in half an hour.

It's fun stuff, and once you get the hang of it you'll never forget, it opens up tons of modding options to have a firm grasp of the theory.

 

[Jamr]

Saving this thread!
If anyone else wants to jump in with more relevant information, it would be nice to have it all in one place.

 

[tntpoof]

as voltage falls so does available amps.it also decreases

 

[bill_delong]

as voltage falls so does available amps.it also decreases

I want to caution that there are many variables to consider with this statement..

This is definitely not the case with post #3 above when I switched from 2S to 4S (increasing voltage) this caused Amps to decrease drastically because I switched from a 4000KV motor to a, 1800KV motor where I was drawing almost identical power in both cases, but I swapped Volts for Amps which made things WAY more efficient, temps dropped drastically and I observed nearly double the run times.

Voltage and Amps are both dependent on Watts (Power Drawn) as defined by Watt's Law (also mentioned above)

Watts = Volts x Amps

 

[Greywolf74]

I think something is twigging I just need to digest one of the posts correctly
Any one find a decent easy diagram of how amps flow and volts ?

As someone who struggled with these same concepts at one point I know how confusing it can be to try and decipher all of this information.

First let me start by trying to help clarify one point about mA and mAh. I know Bill and Tudor did this already but sometimes more explanations can help because I know for myself I can sometimes read 3 or 4 written explanations of something and only one of them might stick.

1) mA (milliamps) is a measure of current, just like Amps only a fraction of a single Amp. For example 5000mA is the same as 5A.
2) mAh is a statement of capacity or how many mA a battery can provide over the course of an hour. So similar to Bill's description above if you are drawing 5000mA (or 5A) from a 5000mAh battery, that battery should last for 1 hour before being depleted. If you're only pulling half of that (2500mA) then the battery will last for 2 hours. If your pulling twice as much or 10,000mA (10A) it will only last for half an hour.

Current, Voltage and Resistance​

"In a circuit, current is the flow of electrons. Voltage is the electrical potential difference between two points. Resistance is something that resists the flow of electrons.

Think about it this way: If you have water running in a pipe, the amount of water running is the equivalent of the current in an electrical circuit.

Then imagine that the pipe is clogged at some point. And only a little bit of water gets through. The water pressure on one side of the clog will be higher than on the other side. This difference in pressure between the two points is equivalent to voltage. You always measure voltage as a voltage difference between two points.

The clog itself would be the resistance.

• Current is measured in Amperes or A
• Voltage is measured in Volts or V
• Resistance is measured in Ohms or Ω

The relationship between current, voltage, and resistance is called Ohm’s Law.

Here is a nice illustration:"

Hope this helps.

 

[WickedFog]

As someone who struggled with these same concepts at one point I know how confusing it can be to try and decipher all of this information.

First let me start by trying to help clarify one point about mA and mAh. I know Bill and Tudor did this already but sometimes more explanations can help because I know for myself I can sometimes read 3 or 4 written explanations of something and only one of them might stick.

1) mA (milliamps) is a measure of current, just like Amps only a fraction of a single Amp. For example 5000mA is the same as 5A.
2) mAh is a statement of capacity or how many mA a battery can provide over the course of an hour. So similar to Bill's description above if you are drawing 5000mA (or 5A) from a 5000mAh battery, that battery should last for 1 hour before being depleted. If you're only pulling half of that (2500mA) then the battery will last for 2 hours. If your pulling twice as much or 10,000mA (10A) it will only last for half an hour.

Current, Voltage and Resistance​

"In a circuit, current is the flow of electrons. Voltage is the electrical potential difference between two points. Resistance is something that resists the flow of electrons.

Think about it this way: If you have water running in a pipe, the amount of water running is the equivalent of the current in an electrical circuit.

Then imagine that the pipe is clogged at some point. And only a little bit of water gets through. The water pressure on one side of the clog will be higher than on the other side. This difference in pressure between the two points is equivalent to voltage. You always measure voltage as a voltage difference between two points.

The clog itself would be the resistance.

• Current is measured in Amperes or A
• Voltage is measured in Volts or V
• Resistance is measured in Ohms or Ω

The relationship between current, voltage, and resistance is called Ohm’s Law.

Here is a nice illustration:"
View attachment 159467

Hope this helps.

That illustration...

 

[Greywolf74]

That illustration...

Dont get my dirty mind started.

 

[leyla1989]

There’s a lot of valuable knowledge in this thread thank you