Going to buy the MCPX-BL

[5hane]

Sorry i missed that mistake , the main thing is not getting the decimal in the wrong place when charging IE 3amp instead of 0.3 amp

No "sorry" necessary. You've all been so patient with me.

Just to pick up on my last message. Can I assume that as the storage charging stopped at 3.7v, that 3.7v is fine for storage?
I haven't tried it yet but I expect that the discharge setting will be 3.7v as well, as has been suggestd it should be.
So discharging will be the same as storing using the Turnigy MAX80W charger.

[kenny d]

they are usually set to about 3.8v but 3.7v will be fine , I usually storage charge to about 3.84v , for me it just means it's closer to full charge & therefore takes less time to top up when needed , the most important thing is don't leave them fully charged for any length of time , Kd

[5hane]

they are usually set to about 3.8v but 3.7v will be fine , I usually storage charge to about 3.84v , for me it just means it's closer to full charge & therefore takes less time to top up when needed , the most important thing is don't leave them fully charged for any length of time , Kd

Excellent. Ta. Perhaps I have a choice and the voltage for different charging processes can be altered somewhere in the settings. II'l look into that later on.

[Peteski]

3.85 V per cell is usually the recommended storage charge, but not so critical. That's the default setting on my iCharger too. I would have thought 3.7 V was a bit low and more like the discharged (to 20% capacity) voltage I see in use.

[5hane]

I now finally have time on my hands so can really try to get to grips with understanding batteries.

Here's a few things still bothering me:

1. Why do they class lipos as 3.7v when they are fully charged at 4.2v? Shouldn't they be called 4.2v lipos?
2. As not everyone agrees that 3.7 is a good storage charge, how do I change the settings on my charger to storage charge at 3.84v or whatever it should be? The only instructions I can find online require a degree in maths to understand.
3. MAH = capacity, but I still cannot get to grips with what volts actualy is. I am reading all sorts of stuff online which attempts to explain, but it's still not fully clicking with me. Why can't a charger just tell me the battery capacity rather than volts seeing as the capacity appears to be the important bit? Plus, how can 4.2v be fully charged and yet take off just 1.2v and the battery is apparently buggered?

Edit: Grrrrrr some of that makes no sense. How can MAH = capacity, because someone said ealier in the thread that voltage indicates how full or empty the pack is, and isn't something full or empty refering to capacity?
Also, how can 3.84v be half full? By my calculations; half of 4.2 = 2.1

[Peteski]

Hi 5hane

In reality voltage is only an "indicator" of the state of charge of the battery (capacity) and in an ideal world voltage would actually be a constant value. But in reality voltage on a Lipo cell happens to drop from a fully charged 4.2V down to 3.7V as the battery cell discharges its current (amps). That's the only way voltage relates to the actual physical capacity of the battery, which is measured in milliamp hours i.e. the amount of current that the battery can provide (amps) over a length of time (hours). So for example a 1000 mAh battery might be capable of delivering a 1A current (1000 mA) for a period of 1 hour or a 2A current for half an hour, or whatever other combination of current/time depending on its maximum current rating and maximum discharge rate. The voltage remains more or less a constant value during this discharge process, but because Lipo cells characteristically do lose a little of their voltage as the battery discharges we can use this characteristic to give an indication of the state of discharge, but only as a percentage of the maximum capacity. So for example 4.2V indicates 100% charge and 3.7V indicates 0% charge. Voltage is not directly related to the actual capacity of the battery at all, but this slight characteristic drop in voltage during discharge of a Lipo cell can be used to give us a very good idea what percentage of the capacity remains.

So to answer question 3, voltage is actually the potential to provide a current flow (amps) against the resistance of an electrical circuit. (Ohm's law states that Voltage = Current x Resistance). A very useful analogy here is a hosepipe where the water pressure is the "voltage", the water flow rate through the hosepipe is the "current" and the the total volume of water discharged is the capacity (flow rate x time). You can see from this simple analogy, that the hose pressure (voltage) doesn't tell you anything about the volume (capacity) of the water supply. In the same way, the voltage of a battery doesn't tell you anything about the battery's capacity either, except for the fact that Lipo cells lose a bit of their voltage (hose pressure) as they discharge. I think this is where you are getting confused in trying to relate voltage directly to capacity as if they are the same thing.

The hosepipe analogy also explains why your charger cannot simply tell you what your battery capacity is. Your charger can see the hose pressure (voltage) and the water flow rate (Amps) but it has no idea how much water volume (Amp-hours) there is available in the tank before it runs out. In other words your charger can only measure what is coming out of the hosepipe, not the capacity of the water supply attached to it.

Hope the above helps to answer question 3 and your final edit. I have no idea how to answer questions 1 and 2. I guess they just took the lowest nominal voltage rating for Lipos, but it doesn't really matter at all.

[5hane]

Hi 5hane

In reality voltage is only an "indicator" of the state of charge of the battery (capacity) and in an ideal world voltage would actually be a constant value. But in reality voltage on a Lipo cell happens to drop from a fully charged 4.2V down to 3.7V as the battery cell discharges its current (amps). That's the only way voltage relates to the actual physical capacity of the battery, which is measured in milliamp hours i.e. the amount of current that the battery can provide (amps) over a length of time (hours). So for example a 1000 mAh battery might be capable of delivering a 1A current (1000 mA) for a period of 1 hour or a 2A current for half an hour, or whatever other combination of current/time depending on its maximum current rating and maximum discharge rate. The voltage remains more or less a constant value during this discharge process, but because Lipo cells characteristically do lose a little of their voltage as the battery discharges we can use this characteristic to give an indication of the state of discharge, but only as a percentage of the maximum capacity. So for example 4.2V indicates 100% charge and 3.7V indicates 0% charge. Voltage is not directly related to the actual capacity of the battery at all, but this slight characteristic drop in voltage during discharge of a Lipo cell can be used to give us a very good idea what percentage of the capacity remains.

So to answer question 3, voltage is actually the potential to provide a current flow (amps) against the resistance of an electrical circuit. (Ohm's law states that Voltage = Current x Resistance). A very useful analogy here is a hosepipe where the water pressure is the "voltage", the water flow rate through the hosepipe is the "current" and the the total volume of water discharged is the capacity (flow rate x time). You can see from this simple analogy, that the hose pressure (voltage) doesn't tell you anything about the volume (capacity) of the water supply. In the same way, the voltage of a battery doesn't tell you anything about the battery's capacity either, except for the fact that Lipo cells lose a bit of their voltage (hose pressure) as they discharge. I think this is where you are getting confused in trying to relate voltage directly to capacity as if they are the same thing.

The hosepipe analogy also explains why your charger cannot simply tell you what your battery capacity is. Your charger can see the hose pressure (voltage) and the water flow rate (Amps) but it has no idea how much water volume (Amp-hours) there is available in the tank before it runs out. In other words your charger can only measure what is coming out of the hosepipe, not the capacity of the water supply attached to it.

Hope the above helps to answer question 3 and your final edit. I have no idea how to answer questions 1 and 2. I guess they just took the lowest nominal voltage rating for Lipos, but it doesn't really matter at all.

Hi Peteski. Thanks for taking the time to explain all of that. I have read and reread it and it is starting to sink in a bit.
I'm going to have to see if there are any evening courses avaliable that touch on the subject of batteries.

I did have a little play with the charger today. The charger gave a reading of 4.20v when the charging ended, although my battery tester gave a reading of around 4.18 (I wont start worrying about that!).
The storage voltage result was 3.80, an improvement over the 3.7 it showed the first time, leading me to think I might have mistakenly selected Discharge the first time around.
It took a whole hour to charge 1 x 160mah lipo, that's slower than the stock single cell charger that came with the heli. I rdad somewhere that it would be ok to increase the amps to 0.2a.

[Peteski]

Hi Peteski. Thanks for taking the time to explain all of that. I have read and reread it and it is starting to sink in a bit.
I'm going to have to see if there are any evening courses avaliable that touch on the subject of batteries.

I did have a little play with the charger today. The charger gave a reading of 4.20v when the charging ended, although my battery tester gave a reading of around 4.18 (I wont start worrying about that!).
The storage voltage result was 3.80, an improvement over the 3.7 it showed the first time, leading me to think I might have mistakenly selected Discharge the first time around.
It took a whole hour to charge 1 x 160mah lipo, that's slower than the stock single cell charger that came with the heli. I rdad somewhere that it would be ok to increase the amps to 0.2a.

Yeah 4.18V is fine, I often find that they settle a tad below 4.2V and your tester could have a slightly different calibration to your charger.

3.80V is also fine for storage charge

The stock e-flite charger charges at 0.3A, which is fine too. Should take about 30 mins at that setting. Your best bet is to get a parallel charge board or harness so you can charge up to 6 batteries at a time.

[5hane]

Yeah 4.18V is fine, I often find that they settle a tad below 4.2V and your tester could have a slightly different calibration to your charger.

3.80V is also fine for storage charge

The stock e-flite charger charges at 0.3A, which is fine too. Should take about 30 mins at that setting. Your best bet is to get a parallel charge board or harness so you can charge up to 6 batteries at a time.

Cool ill increase the amps. I thought it might damage the batteries, but if the stock charges at 0.3a it should all be fine I guess.
I'm pretty sure I have what's needed to charge all 6 at one time- the charge harness, so will try that next time.

[Peteski]

Cool ill increase the amps. I thought it might damage the batteries, but if the stock charges at 0.3a it should all be fine I guess.
I'm pretty sure I have what's needed to charge all 6 at one time- the charge harness, so will try that next time.

Yeah, 0.3A is a 2C charge rate on a 160 mAh battery, which is perfectly safe and a good compromise between charging time and battery life on these little cells. If you are charging 6 of them in parallel, don't forget to increase the overall charge rate to 6x0.3 = 1.8A as the current is shared between them all. Also make sure they are all in the same state of charge too (within about 0.02V of each other)

[dillwhacker]

Peteski, I think you need some new beads on ya abacus dude LOL..

6x0.3 = 1.2A
(within about 0.02V of each other)

And 0.02V is very very tight, 0.2V is fine for paralleling up, IMO.

[Peteski]

Peteski, I think you need some new beads on ya abacus dude LOL..

And 0.02V is very very tight, 0.2V is fine for paralleling up, IMO.

Oops, corrected now to 1.8A (I was actually charging 4 of them at 1.2A while I wrote it and got confused!)

I'm sticking with 0.02V match for parallel charging though. 0.2V is a big difference in actual state of charge as there is only about 0.5V difference from flat to full charge. Maybe I'm being too cautious? Or maybe state of charge is really unimportant?

[5hane]

Thanks both. Will be trying not to burn the house down shortly

[dillwhacker]

Well, Ok, I tend to be a bit cavalier with these things, but 0.02V is a very close match - like closer than most multi-cell LiPos match internally cell-to-cell.
Maybe with big >5000 mAh batts you need to be careful, but I still think you are safe with a fused balance board.
With tiddly little LiPos, the internal resistance is large relative to the voltage difference, so I would just say avoid full charge / flat, but otherwise don't worry, just connect them up and charge.
IMHO

[Peteski]

Well, Ok, I tend to be a bit cavalier with these things, but 0.02V is a very close match - like closer than most multi-cell LiPos match internally cell-to-cell.

My multi-cell lipos are all matched within 0.01V across cells, I've never actually seen one of mine out by more than that. I do always balance charge them, but I presume everyone does.
Maybe you are right about the 1 cell batts not being important to match when charging, but I just do it anyway for good practice. Obviously for a multi-cell pack, 0.02V is proportionally less of the total battery voltage and therefore I would adjust my matching limit accordingly.