Chargers How are you charging at your flying site?

[fhu667]

Right now I charge at home, fly what batteries I have charged and then go home. However, that is about to change, and I would like to be able to charge at the flying site. I currently have two server power supplies powering an iCharger 306B, and it will be necessary to charge 6s batteries.

I have a 3500kw generator that was given to me, but that thing is a beast to load in the truck. It's also a pain to move in and out of the garage.

My truck uses dual batteries, so I don't know if I'd really run the risk of running down my truck batteries to where it wouldn't start. Is it at all practical to attach an inverter to the battery? It seems like it would be inefficient to convert dc to ac, and then convert it back to dc. Also, if my battery charger is 1000 watts, then I'll need an inverter capable of more. Is 1200 watts enough, and I wonder how long I can charge before my truck won't start?

I could also buy a couple of deep cycle batteries and connect them in a series. That would give me 24 volts, and I think I could supply this straight to my charger. Will this work?

Lastly, I could only fly where there is power available. I don't like that option, but I know one of you guys was going to say it!

Please comment.

 

[Slobberdog]

you can run a 12v battery and get 60 amp hours out of it, therefore getting the full potential out of the charger,

you only have to run 24v on your ps because your only putting 110v in on the ac side, I run a single hp 1200w ps off 240v here in the uk and get my 30 amps available.

 

[fhu667]

I don't have to have 24 volts? Maybe I need to read up a bit because I certainly don't understand. Let's see....
@12V - 500W
@24V - 1000W
But I can still run 30 amps on either?

Let's make an example of what I want to do. I'm also doing a little research as I type this, so correct me if I'm wrong. Let's say I have 2 - 5000mah 6s packs that are capable of being charged at 5C. And of course I want to parallel charge at the field.

My math tells me that I could charge them at a rate as high as 50 amps.
Amps * number of batteries * charge rate multiplier (c rating).

However, I'm only going to be able to set my charger to 30 amps for the charge rate, because that's all she'll do.
So if Watts = Volts * Amps, then that means i have 50.4 volts (2 - 6s batteries) * 30 amps = 1512 Watts. At 24 volts I only have 1000 watts available, and I have half that at 12 volts.

So with some reverse logic somewhere.....
Amps = Watts / Volts
1000 Watts / 50.4 Volts = 19.84 Amps (with a 24 volt power supply)
500 Watts / 50.4 Volts = 9.92 Amps (with a 12 volt power supply)

What does this mean? Well I'm not sure other than the fact that it's going to take longer to charge my batteries. How much longer? I think a 5000mah battery would take one hour to charge at 5000mah. I am no electrical expert, and I'm reading as I go. So if that is correct, then I need to charge 10,000mah, or 10 Amps. If I have 9.92 available with a 12 volt supply then that sounds to me like it would take just a fraction over an hour to charge my batteries with a 12 volt power supply, and just a bit over a half hour (0.504 hours or 30.24 minutes).

Now what I'm not sure of if there are some changes that make these calculations incorrect due to losses or inefficiencies. Hell, I'm not even sure if any of it is right! However, if I'm anywhere close on this it means that depending on my charge voltage I can fly once an hour or once every half hour if I only have one set of batteries for my 700.

As I said, I'm not sure about the match, but I think it's right. I give the following link credit for helping with my calculations: Understanding wattage in relationship to charging - TJinTech

 

[Slobberdog]

If you are para charging 2 6s batts then the voltage is 25.2v max and the amperage is doubled, you are still charging a 6s but you have 2 times the capacity.

What I was saying about the battery is slightly wrong in effect to get what you need

you would need a 300 amp hr bank at 12v to give you 1.5 hrs of charging capability at full power on your charger, so maybe not so price effective,

When it comes to the server power supplies they are rated 110v - 240v input and at 240v the supply will give you 12v output and depending on what supplies you have, the dps600pb supply will be 12v and 47amps at 575w but as you reduce the input voltage these values go down that's why you have to double up the supplies,

So if you have full input on one ps then you would have 575w out / 25.2v for your 6s packs would give you a max charge capacity of just over 22amps

 

[fhu667]

But here in the states we don't have 240v in our homes as a general rule. Most of us are at 110v. I wonder if that's why you only need one power supply in the UK? I have no idea what the output difference is at 110v compared to 220v.

 

[Slobberdog]

Not sure on most of them but here's my second charging power supply stats for you to see why I went for this option,

 

[fhu667]

And I guess if I go back to my first question about using deep cycle batteries, I would in fact need two of them to get maximum affect. At least it appears that way to me.

 

[cml001]

Generator!

 

[Slobberdog]

It would depend on the amp hr rating of the battery, but looking at the figures yes you would,

As cml001 has said above a genny is the easiest option,

 

[Stambo]

I would look for a VSR (voltage sensitive relay) and the largest 12v deep cycle battery you can afford.
Even a used one will do for a start.
Hook it all to your truck with some sort of quick disconnect plug and there is your power supply.

The VSR is designed to only connect the battery to the truck when the voltage is above about 13.5V.
This means while you are stopped the deep cycle battery is isolated, starting batteries are safe, start the truck and charge voltage rises above 13.5V so the deep cycle gets charged.
Used to use these for motor homes in a previous job to isolate the starting battery from the house battery.
You could monitor it with a volt meter if you wish.
Once you see how well it all works you could look at a second deep cycle if required.
In between times you could run the truck for a while to charge the deep cycle.

Using an inverter to convert to AC then a power supply to go back to usable voltage would be very inefficient.
You would still need a deep cycle battery to prevent flattening the start batteries.

In fact just the deep cycle would do for a start.
Charge it at home and see how many charges of your flight batteries you can get out of it.

You could even isolate one of your truck batteries and see how well it starts on the other.
Although cycling a starting battery like that would reduce its life quite a bit.

Lastly, even though your batteries may say that they are capable of 5C charge rate I would be hesitant to do so too often.
My Zippy Compact 4S 5000 say 5C but I rarely charge at over 1.5C or 7.5 amps.
I figure slower charge is more conducive to longer life.

 

[fhu667]

Man that generator is a back breaker. Although it would be a good reason to use it.

 

[Slobberdog]

Others on other sites have gone for generators like the Ryobi RYi 2200, home depot have them and they look a good size to haul around, but at $600 its not cheap but then I don't know what a deep cycle battery would set you back.

 

[fhu667]

Even one deep cycle doesn't give me all the power I'd like to have, but I do have an idle one in the garage that I can test with.

I think I'll look for some casters to mount on the generator, and see if I can find a way to make it a little easier to haul around. At least if I use it I'll know it works if I ever need it. I don't even know if it will start now since it's been sitting idle for a few years.

- - - Updated - - -

but i'm sure i can get it to start.

 

[pvolcko]

6s = 25.2v (full charge, 22.2v nominal).
5000mAh packs.

At 5C you're talking 25A at 25.2V output so equiv wattage of 630W per battery. Assume 90% efficency in the powersupply and charger so 700W input to the charging system per battery.

1400W if you're para-charging two at the same time.

If you're running 24V serial connected batteries for a power source that means for 1400W of input power roughly 60A at 24V. That's all in Ah actually, so 60Ah, if the charge ran full blast for one hour. At 5C you're talking maybe 10 minutes to charge them up, or roughly 10Ah would be drawn off the batteries per charge per pair of packs, or 5Ah per single pack (lo and behold, the capacity of the pack!).

Soooo... Your deep cycle battery bank should be sized to cover the number of times you want to recharge, plus some buffer (I'd say 20%) so you aren't overdischarging them, and the capacity of the battery you are charging is a good rough estimate of the capacity you'll draw off the deep cycle battery bank per charge (you're only actually charging up 70% or so of your pack capacity, but inefficiency will draw up the rest of the estimate). So for 10 pack recharges at the field, you'll want 5Ah * 10 * 1.2 = 60Ah of battery capacity. Rough deep cycle $/Ah is $2 and you need two batteries for each Ah to get up to 24V input so you'll spend about $220 to get a battery bank for 10 charges at the field.

Just realized I didn't account for the 25.2V output voltage vs 24V input voltage difference, so instead of 60A at 24V it is probably 63ish A instead, or 5.25Ah per pack drawn from the battery bank. 63A of bank capacity needed instead of 60Ah, etc.

Of course, you also said your charger will only do 30A output max. Luckily that doesn't change the capacity calcs, it will simply limit how fast the flight packs will charge up. Instead of 10mins it might take 15 to 20.

 

[Slobberdog]

6s = 25.2v (full charge, 22.2v nominal).
5000mAh packs.

At 5C you're talking 25A at 25.2V output so equiv wattage of 630W per battery. Assume 90% efficency in the powersupply and charger so 700W input to the charging system per battery.

1400W if you're para-charging two at the same time.

If you're running 24V serial connected batteries for a power source that means for 1400W of input power roughly 60A at 24V. That's all in Ah actually, so 60Ah, if the charge ran full blast for one hour. At 5C you're talking maybe 10 minutes to charge them up, or roughly 10Ah would be drawn off the batteries per charge per pair of packs, or 5Ah per single pack (lo and behold, the capacity of the pack!).

Soooo... Your deep cycle battery bank should be sized to cover the number of times you want to recharge, plus some buffer (I'd say 20%) so you aren't overdischarging them, and the capacity of the battery you are charging is a good rough estimate of the capacity you'll draw off the deep cycle battery bank per charge (you're only actually charging up 70% or so of your pack capacity, but inefficiency will draw up the rest of the estimate). So for 10 pack recharges at the field, you'll want 5Ah * 10 * 1.2 = 60Ah of battery capacity. Rough deep cycle $/Ah is $2 and you need two batteries for each Ah to get up to 24V input so you'll spend about $220 to get a battery bank for 10 charges at the field.

Just realized I didn't account for the 25.2V output voltage vs 24V input voltage difference, so instead of 60A at 24V it is probably 63ish A instead, or 5.25Ah per pack drawn from the battery bank. 63A of bank capacity needed instead of 60Ah, etc.

Of course, you also said your charger will only do 30A output max. Luckily that doesn't change the capacity calcs, it will simply limit how fast the flight packs will charge up. Instead of 10mins it might take 15 to 20.

Nice explanation Paul.........

 

[fhu667]

Thanks for that explanation. It does make sense.

 

[cml001]

U have a generator! I'll trade u a interstate battery that's less than a year old for the genny!