Cant decide on a power supply

[Adiabatic]

18V max input is pretty low and that's why you need such a high current to get 800W output. D6+ for example accepts up to 30V DC and therefore only needs about 22A + losses due to <100% efficiency (I have read 90% power efficiency for DC-DC converters at these loads, which would be about 24A input, but 60W waste power, seems too high/underestimating efficiency, charger doesn't get that hot and the fan doesn't run that much) to reach its peak output of 650W.

I think you can get away with less than 60A supplied to that charger, though. Assuming 100% input-output efficiency, at the maximum input voltage of 18V you'll need 45A. At 90% efficiency, you'll need 49A.

 

[slick2500]

18V max input is pretty low and that's why you need such a high current to get 800W output. D6+ for example accepts up to 30V DC and therefore only needs about 22A + losses due to <100% efficiency (I have read 90% power efficiency for DC-DC converters at these loads, which would be about 24A input, but 60W waste power, seems too high/underestimating efficiency, charger doesn't get that hot and the fan doesn't run that much) to reach its peak output of 650W.

I think you can get away with less than 60A supplied to that charger, though. Assuming 100% input-output efficiency, at the maximum input voltage of 18V you'll need 45A. At 90% efficiency, you'll need 49A.

Eh I haven't come close to maxing out the 12v power supply that I have as I never end up anywhere near 400w when charging so I'm not too worried about it. Just kind of annoying that if ever wanted to use this charger to its full potential I would have to jump through a few hoops to do so. It's been trucking along for 5 years now so I can't complain too much I guess.

 

[Adiabatic]

I agree that this kind of extra power isn't needed in most circumstances, especially if the charger only has two channels to put it through and you don't like parallel charging. I charge two of the largest batteries I'd be willing to put in an R/C at 1C simultaneously and only just come close to maxing out the D6+ on AC.

 

[jkflow]

This is something that I still struggle to make sense out of, you have some of these DC chargers that require a 30v 1400w 60a power supply to be able to utilize their full power but trying to find a power supply that can actually output that much power is not that easy. I found one on eBay that is 30v and 1400w but only 47a. For my charger I need 18v, 800w and 60a.
Input Voltage Range: DC 12 - 18 Volts DC
Required Input Amperage: 60 Amps
Charger Circuit Power: 400 Watts x 2

A little math is at hand.
800W is what the charger can handle, at 12V that is 66.6A i.e. it won't even be able to generate 800W and be limited to ~720W
At 18V it's ~44A. Add ~ 10% loss for efficiency i.e. the 47A is pretty close to ideal.

https://www.ebay.com/itm/124771721992

 

[slick2500]

A little math is at hand.
800W is what the charger can handle, at 12V that is 66.6A i.e. it won't even be able to generate 800W and be limited to ~720W
At 18V it's ~44A. Add ~ 10% loss for efficiency i.e. the 47A is pretty close to ideal.

https://www.ebay.com/itm/124771721992

I thought it was less than that on 12v I could have swore someone else told me in another thread it was closer to like 400w. My psu is 12v 900w and 75a.

 

[Adiabatic]

His math looks right. At 12V you'll be limited to 720W input and ~650W output assuming 90% efficiency and a supply that can output 60A.

 

[KnowAir]

I've been contemplating ugrading chargers recently myself. I'm undecided as to what route I am going to take built in or external power supply. The one thing I wanted to add is how important the finishing rate is on a charger. My cheapo skyrc knockoffs take an unbelievable amount of time to finish! I usually end up shutting them off after 30 minutes at .1A..

 

[Adiabatic]

Can't comment on most other chargers but I have a D6+ and HTRC C240, both take around 40 minutes total to charge and balance from storage voltage at 1C.

 

[KnowAir]

Can't comment on most other chargers but I have a D6+ and HTRC C240, both take around 40 minutes total to charge and balance from storage voltage at 1C.

With what size and cell count? My cheapo chargers will bring a 3s 5500mah up to 12.5V in about an hour(from lvc), then take another hour to finish!!
Not complaing since I paid about $25 each..but recently I've become more concerned of the fire hazard these non regulated/UL listed chargers present.
Sorry OP, I have a bad habit of hijacking ✌

 

[Adiabatic]

I only do 3s (5000-6000mAh) on the C240 because it can only output a maximum of 100W on one channel and that's not enough to charge my 6s 5200mAh packs at 1C. D6+ gets the 6s packs and sometimes the 3s. The 6s take slightly longer to balance at the end, but no more than 5 extra minutes on average.

 

[Monster Dork]

I'm very much anti-fire, so I only charge one batt pack at a time on my single-channel charger.

Do not put switching power supplies in parallel. If you don't know why this is a bad idea, you should do some homework before hotboxing your bedroom with Lipo smoke.

One search for Meanwell switching power supplies should net you exactly the PSU you need. Pick your voltage (higher to rated max is more efficient), pick your wattage (based on biggest battery(-ies) you charge, and you're done.

Remember, max charge rate occurs at the beginning of the charge, and quickly drops off. You don't need much head room, just enough is fine.

Have fun, and keep a big bucket of sand ready for any arithmetic errors.

 

[jkflow]

Placing power supplies in parallel can be very tricky. You need to know what you are doing, series is a little easier, but there is the 'ground' that needs to be taken into account. Plenty of tutorials on Youtube for the cheap supplies.

There are 3 magic numbers for chargers.
1) Max voltage (6S, 8S etc)
2) Power per channel (needs to be 150W for a meaningful charge on 6S)
3) Balance current. Minimum of 1A or you will grow a beard watching them balance.

For DC chargers, pay close attention to the max rated input current. That will determine the max power and the minimum voltage required to get to that level.

 

[Adiabatic]

For the sake of brevity I didn't go into detail but yes, you should only connect PSUs in parallel if they're capable of load sharing, otherwise the voltage difference will cause problems. Many have a load sharing pin that must be connected between them in addition to the usual parallel wiring. Pretty common setup that the airplane guys use but you need to have some technical knowledge to build safely.

 

[Jerry-rigged]

On the comment about finishing the balance taking an hour - that is half the charger and half the battery. My lower quality packs are not matched as well, and so the LVC voltage will be off by a tenth or so. Then on the charge side, that same cell will lag again, so by the time you get to the balance stage, that cell is now 2-3 tenths off, which adds to the balance time.

My higher quality packs will LVC with each cell within a few hundredths, so when they hit the balance stage, they are often still closer than a tenth of a volt apart, so there is less balance to do.

All that, plus 2c charging means about 20 minutes total charge time from storage charge.

 

[chevys10zr2003]

I'm very much anti-fire, so I only charge one batt pack at a time on my single-channel charger.

Do not put switching power supplies in parallel. If you don't know why this is a bad idea, you should do some homework before hotboxing your bedroom with Lipo smoke.

One search for Meanwell switching power supplies should net you exactly the PSU you need. Pick your voltage (higher to rated max is more efficient), pick your wattage (based on biggest battery(-ies) you charge, and you're done.

Remember, max charge rate occurs at the beginning of the charge, and quickly drops off. You don't need much head room, just enough is fine.

Have fun, and keep a big bucket of sand ready for any arithmetic errors.

So you don't like my charging setup? Charging 12 batteries from a 2 channel charger.

 

[Adiabatic]

All you need to complete that setup is a few containers of flammable liquids, reloading powder and maybe some 1.3G commercial fireworks lying around on the bench.

 

[chevys10zr2003]

On the comment about finishing the balance taking an hour - that is half the charger and half the battery. My lower quality packs are not matched as well, and so the LVC voltage will be off by a tenth or so. Then on the charge side, that same cell will lag again, so by the time you get to the balance stage, that cell is now 2-3 tenths off, which adds to the balance time.

My higher quality packs will LVC with each cell within a few hundredths, so when they hit the balance stage, they are often still closer than a tenth of a volt apart, so there is less balance to do.

All that, plus 2c charging means about 20 minutes total charge time from storage charge.

The big thing that made a huge difference for me was getting a charger with a much better current drain for lipo balancing. I went from a Hitec X4 AC Plus which has a 300ma per cell drain to a Hitec X2 700 which has 800 and the final step of the balancing get dramatically faster.

 

[Monster Dork]

So you don't like my charging setup? Charging 12 batteries from a 2 channel charger.

As far as I am concerned, no, I don't like. I had a balance board burn up on me, I'm lucky the house didn't go with it. I don't trust ten-way splitters. One battery per balance lead is it for me now. But at least I ain't homeless. YMMV, IDGAF.

 

[chevys10zr2003]

As far as I am concerned, no, I don't like. I had a balance board burn up on me, I'm lucky the house didn't go with it. I don't trust ten-way splitters. One battery per balance lead is it for me now. But at least I ain't homeless. YMMV, IDGAF.

I only do that for the initial charge before I go out. After that they get charged individually. You definitely need to know what you're doing with it or you can mess up a lot of stuff in a hurry.

 

[KnowAir]

On the comment about finishing the balance taking an hour - that is half the charger and half the battery. My lower quality packs are not matched as well, and so the LVC voltage will be off by a tenth or so. Then on the charge side, that same cell will lag again, so by the time you get to the balance stage, that cell is now 2-3 tenths off, which adds to the balance time.

My higher quality packs will LVC with each cell within a few hundredths, so when they hit the balance stage, they are often still closer than a tenth of a volt apart, so there is less balance to do.

All that, plus 2c charging means about 20 minutes total charge time from storage charge.

Welp, that could be my issue..cheap batts PLUS cheap charger