Max AMP

[Hoochykins]

What would you say the max amperage is I can use charging from a 4S/5S 5000 to 3S 2200 in the field with a ISDT Q6? Using deans connectors (if it makes any difference).

 

I usually charge at home with 5 - 7 amp but didn't want to push it from lipo to lipo if it could cause an issue?

Edited August 17 by Hoochykins

[Chris Walby]

First point IMO charging a 3S2200 at 7A is not best practice, 2.2A and perhaps 4.4 (2C), but not over 3C . A discharged 3S2200 to 30% is only going to take 45 min to charge so why you need to do it in 15 min seems unnecessary. For the cost of a couple of extra 3S2200 you could fly three times and after the second flight have a couple on charge.

 

Second point from experience using 4S5000 packs to supply a charger is that the charger will over discharge the supply pack to a pint of damage so you have to keep a near constant watch on it. E.G. 4S5000 charging 3S2200 packs. As a rough approximation and based on how hard you discharge the supply battery you would be ok charging your first 3S2200, but the second pack at worst case would take you to 4400mAh but that would take your supply battery to 12% charge left and its damaged at that point.

 

Could parallel the 4S5000 packs (of the same cell count) to add supply battery capacity, but again it will not stop the charger overly discharging the supply battery if the packs on charge are not fully charged.

 

PS a typical car battery is 54Ahr and the charger will probably cut out on low supply voltage before the supply battery is damaged.

[Ron Gray]

I know that I have posted this before but I now charge my Li-Po batteries at 3 or 4C, in fact I've also charged at 5C and the batteries haven't suffered as a result. You obvs need the power supply to be able to charge at these rates!

[Chris Walby]

Only from my perspective as I use GNB packs, but the manufacturer is quite clear as to their recommended charge rate. Copied from their advice sheet:

 

Would be interested to see what other manufacturers state as acceptable charge rates and whether the optional temperature probe on the charger must be used?

 

[Ron Gray]

For years the ‘accepted’ charge rate has been 1C but a post on this forum earlier this year prompted me to try higher rate charging. I originally started out at 3C and kept a close watch on temp but as this didn’t really alter I started to push it further with the same results. I should add that I only charge to 4.16v and try not to go below 30% remaining capacity when flying. Many charges later and the Li-POs are still OK!

[Cuban8]

Bought some new 3S 3000 lipos recently and the manufacturer's sticker on them quotes to charge at 1C only. I believe that this is a very conservative figure and although I don't push it too far or indeed have any real need to super quick charge at high rates, I'm sure it's very possible but with all the usual caveats being closely observed. I find 1.5C charging fine for my needs.

 

[Duncan Disorderly]

 

...now at 699 cycles each, with 499 of those charges at 12A  (3.6C) and I can't fly any faster than that, so two LiPos is all I need.

 

I'm told the Turnigy post-pandemic cells/QC haven't been as good, so next up on test will be a load of these:

[MattyB]

6 hours ago, Hoochykins said:

What would you say the max amperage is I can use charging from a 4S/5S 5000 to 3S 2200 in the field with a ISDT Q6? Using deans connectors (if it makes any difference).

 

I usually charge at home with 5 - 7 amp but didn't want to push it from lipo to lipo if it could cause an issue?

What is the discharge c rating of the 4S and 5S chargers packs? Personally with a setup like this I would stick with a 1-2C charge at max

[Chris Walby]

My reply was based on the information quoted in the OP and no doubt they can be charged at a higher rate with caveats like don't charge above x volts or discharge below y voltage so reverted to my known manufacturers guidance.

 

I charge off  12V DC power supply or the van's leisure battery 12V DC, so if you take DD's 6S4000 pack charged at 5C on the input side the charger will be pulling 40A.

Sorry but there is no way I am standing over the charger with its fan on full tilt and discharging the charger battery that hard just so I can have a flight pack in 8 minutes. I just buy another lipo or fly another model while I wait for the used pack to cool before charging at 1C, it will be ready in less than 45 minutes anyway.

 

At one of the clubs I fly from we have PV charged battery packs (sealed PB) and the most frequent problem was people charging high cell count packs (6S+) or the quantity of people charging at once. It only take 6 people with twin chargers (some have quad units) charging 4000 to 6000 packs at 1C and the average of 40A, if they  all go for the 5C option that's 200A. That is within the rating of the protective device, but done repeatedly it won't do the batteries much good and will find any weak points in the installation.

 

I can see why people might want to charge at 5C, but with all the additional precautions can't really see the benefit.

• If the pack has just been flown then it should be left to cool before charging, so the lipo won't be ready in 8 minutes anyway
• If charging at 5C the pack will get warmer than being charged at 1C, if there is no temperature detection then its best if you stand and watch it every second its charging
• Once charged at 5C the pack temperature should be checked before flight
• The supply has to be rated for the high current required
• Operating charger at higher currents (temperature cycling the electronic components) will shorten its life
• Its less efficient due to I2R losses

Manufactures engine advice, fuel up, start up, warm up, tune for max RPM and then give it a good thrashing, land refuel and repeat...sounds simpler that constantly watching lipos charge 🙂  

 

So what circumstances necessitate charging packs at 5C? 

[RottenRow]

Charging the 3S packs at 5 to 7A won’t cause an issue as far as current drawn from the supplying pack is concerned, as this will be a bit less than this at 4S and a bit lower still at 5S, though there will also be a small current to power the charger’s electronics. This will be well within the discharge rating of those packs (which will be capable of delivering many tens of amps).

 

However the problem comes, as others have stated, with not knowing to what level the supplying pack is becoming discharged, and terminating the charge before the supplying pack becomes excessively discharged.

 

That issue would exist irrespective of the charging current (1C, 3C or whatever) as you would still be drawing a certain proportion of the supplying pack’s total energy during each charge cycle.

 

Brian.

[Duncan Disorderly]

31 minutes ago, Chris Walby said:

So what circumstances necessitate charging packs at 5C? 

 

Read the thread I quoted. It would be unfair on the OP to repeat all of it here.

 

I find 3C or 4C hits the spot nicely, based on a fairly long term experiment. Do whatever works for you.

 

35 minutes ago, Chris Walby said:

If the pack has just been flown then it should be left to cool before charging, so the lipo won't be ready in 8 minutes anyway

Why? Mine charge/fly/charge/fly/charge/fly sometimes all day. They are ready in 10 minutes.

 

36 minutes ago, Chris Walby said:

If charging at 5C the pack will get warmer than being charged at 1C, if there is no temperature detection then its best if you stand and watch it every second its charging

They get about as warm as when they fly, so they stay the same temperature pretty much all day.

 

37 minutes ago, Chris Walby said:

Once charged at 5C the pack temperature should be checked before flight

Just warm to the touch. It's brilliant in the winter.

 

37 minutes ago, Chris Walby said:

Operating charger at higher currents (temperature cycling the electronic components) will shorten its life

As I said, 200 charges at 1C then 499 charges at 3.6C and still going strong. If this is reduced life then I'm cool with that for a £38 LiPo and a £50 charger.

 

39 minutes ago, Chris Walby said:

 

At one of the clubs I fly from we have PV charged battery packs

I provide my own Li-ion power pack because unless your club also buys your glow & petrol why provide leccy? Reading a recent thread on here about glow fuel prices, it's your IC flyers that you need to be subsidising as it's far more expensive than electric flight.

 

44 minutes ago, Chris Walby said:

then give it a good thrashing, land refuel and repeat

It is exactly the electric equivalent of this.

 

 

[Duncan Disorderly]

8 hours ago, Hoochykins said:

push it from lipo to lipo

 

Get  matey on BMFA Classifieds to make you up a 6S2P Li-ion pack, or make one yourself. Lots of advantages to doing it that way.

[Hoochykins]

A lot of info here!

 

I usually charge my 3S 2200's at 5a which is just over 2C if I'm correct? (Still new to it all) Only now and again if I need to charge quick before I leave I'll stick one on at 7a.

 

Also I'm only charging once or twice off a 4S 5000 as I got quite a few secondhand so I wouldn't want to use them flying, only charging in the field. I didn't think about over discharging them but it's a good point, I'll stick one of those cheap monitors on the balance cable so it will alarm when it's discharged to its safe level.

 

 

 

The jist I've got is I don't need to worry about discharging the source lipo to hard 👍🏻

 

I'll take a look at the 6S2P Li-ion, might invest in something like that next spring.

[Philip Lewis 3]

1 hour ago, Duncan Disorderly said:

 

They get about as warm as when they fly, so they stay the same temperature pretty much all day.

 

Just warm to the touch. It's brilliant in the winter.

 

Ideal temperature to operate a LiPo battery, about 35C.

 

So long as it isn't actually hot why not recharge it? In the winter it is likely to be quite beneficial to the pack as the one thing LiPo's don't like is being charged and used when cold.

[Duncan Disorderly]

2 minutes ago, Hoochykins said:

I'll stick one of those cheap monitors on the balance cable

 

Yes, or set the minimum input voltage level on the Q6 so it cuts out

 

4 minutes ago, Hoochykins said:

I'll take a look at the 6S2P Li-ion

 

It may save you tons of money in the long run. Or even the short run. Just scale it to your needs (mine are 6S8P). Have a look at the chargebox thread (it's quoted in the 4C charging thread).