CSM SL720 and cold weather

[Dedcalm]

I was under the impression that taking a fully charged (4.2V) warm Li-Po into the cold would cause over voltage thus risking cell damage as a result of essentially over charging it... My CellPro 10S has been charging on Cold Weather program for the last couple of weeks in my un-heated workshop. As such my packs dont suffer any 'thermal shock' issues of taking them out in freezing temps.

[Rotorhead]

Your impression is correct

[Ashley Davis]

the threads you reference all talk about 'no power' in the cold. Since all our motors work off of voltage (ie. KV or 'RPM per volt') how do you explain that nobody sees their headspeed go through the roof in the cold?

Surely if the voltage goes up then we should all be seeing better RPM from our machines and more power.

Sadly this isn't the case. It's also a totally moot point as the voltage to the gyro and rx was regulated, so the regulator would draw whatever it needed to make the voltage required for the rx. With a 2S lipo it's reducing the voltage, so unlikely that voltage is an issue here.

Essentially we are probably discussing very different things, you are talking about static voltage and I'm taking about loaded voltage or power delivery capability.

With regard to lipo storage the packs should be charged to 40% and then kept cold. Not because of voltage problems but because the chemicals degrade quicker if held in a high state of charge. If you reduce them to 40% charge and make the pack cold (refrigerate) then it stops degradation of the packs internals as the chemicals are less active in the cold. Freezing is a definite no no.

The Cellpro cold weather charging is because of capacity reduction not over voltage as explained earlier. Otherwise it would terminate the charge early due to this increased voltage in the cold would it not? Cold weather charging takes account of capacity reduction and also reduces the charge rate as the resistance of the pack to take charge is higher in the cold.

[J3DI]

I had an SL720 that played up once, turned out the temperature calibration data was somehow corrupted in the gyro. Returned it to CSM and they reflashed and updated the firmware and all was good again...

[Rotorhead]

the threads you reference all talk about 'no power' in the cold.

Keep reading and you will see the people talking about the voltages going up when you take a pack from the warm into the cold.

Since all our motors work off of voltage (ie. KV or 'RPM per volt') how do you explain that nobody sees their headspeed go through the roof in the cold?

Surely if the voltage goes up then we should all be seeing better RPM from our machines and more power.

Because .1 or .2 of a volt is not a lot of an increase, and the lower current supply ability causes a drop in the on load voltage, effectively the packs C rating has been reduced, and that means a greater fall in voltage for a given current draw.

Also we are talking about rx supplies on nitro helis here not main power on electric helis, so the loads are going to be considerably less than on an electric model.

Apples and oranges mate.

Sadly this isn't the case. It's also a totally moot point as the voltage to the gyro and rx was regulated, so the regulator would draw whatever it needed to make the voltage required for the rx. With a 2S lipo it's reducing the voltage, so unlikely that voltage is an issue here.

Yes, and the point I was making was that CSM's claim that it could have been a low voltage issue was doubly wrong, because of that and he took a lipo from a warm environment into a cold one.

Essentially we are probably discussing very different things, you are talking about static voltage and I'm taking about loaded voltage or power delivery capability.

And under small loads the static voltage will vary only a very small ammount, and thats what is the case here, no motor to be driven, no inflight loads, its not even started yet, just turned on, servos at next to no load...... near as static as you can get with everything on.

With regard to lipo storage the packs should be charged to 40% and then kept cold. Not because of voltage problems but because the chemicals degrade quicker if held in a high state of charge. If you reduce them to 40% charge and make the pack cold (refrigerate) then it stops degradation of the packs internals as the chemicals are less active in the cold. Freezing is a definite no no.

And if you charge them to say 8.4v (2s) and then cool them the voltage would go over 8.4v, which would risk greatly the packs health, discharging to 40% would put the voltage much lower than 8.4v, so any increase due to cooling from that point on would not be enough to go over 8.4v.

The Cellpro cold weather charging is because of capacity reduction not over voltage as explained earlier. Otherwise it would terminate the charge early due to this increased voltage in the cold would it not? Cold weather charging takes account of capacity reduction and also reduces the charge rate as the resistance of the pack to take charge is higher in the cold.

The reduction in the capacity causes an effective increase in voltage, you've still put in the same ammount of energy into the pack, but its capacity has lowered, that causes an increase in the voltage until the pack is warmed up again.

I hate using analogies, but think of it like a balloon in a pressure chamber, you inflate the balloon (charge it) then crush it with an external pressure (drop the temperature) the ammount of air in it hasnt decreased, but its volume has, so that air in there has increased in pressure (kinda like electrical pressure )

[Ashley Davis]

At this point we are just agreeing with each other, so I'll leave it at that. The key point I wanted to surface was that cold affects capacity.....this has knock on effects but to understand it all you have to view the effect as a capacity change. Once you do that the rest makes sense.

[squeaky pete]

I've been using CSM gyros for quite a few years now, even flown in 1ft deep snow whilst still snowing (T-Rex 700e) and not had an issue with the cold. It's more likely for the rest of your electronics to fail first.

Trev

thats just hardcore!!!

[steveru]

Thanks guys for all the replies.

Quick update:

I'm convinced that the Gyro has developed a fault or is just a big woose!!

Todays weather was warmer than the weekend with a high of 5 deg C but felt colder due to the wind.
The heli was placed outside to acclimatise and a fresh 2250mAh 2S Lipo battery was connected to the 2 in 1 regulator. When switched on the cyclic, throttle and mixture servos all jumped into life and the 720 REV light illuminated but not the SET light! Using my fingers I gently warmed the gyro being very careful not to disturb the connecting wires. After just a couple of minutes I tried again and this time the gyro servo moved into centre position and the SET light came on. The heli and gyro worked faultlessly throughout the flight until I switched the heli electrics off and then back on as the gyro didn't SET. A quick warm up and then off we go again

Therefore, I think I'll be returning it to CSM to be replaced or de-woosed!!

Regards,
Steve

[gramey]

Well I can vouch for the fact the battery was fully charged and full green lights were showing on the 2 in 1 yet the gyro still wouldn't set. Perhaps you should have followed the advice you give others and bought another 770, proper gyro that, not one of those gay plastic things!