R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Radio and Electronics

Reply
 
Thread Tools Search this Thread
Old 04-08-2015, 10:20 AM   #16
Tech Master
 
Join Date: Jan 2006
Location: El Mirage, AZ, USA
Posts: 1,320
Trader Rating: 4 (100%+)
Default

Everything these guys have said I agree with. BUT......

This the rule of thumb i have always used and has never failed me yet. Of course somebody will disagree bit o well take it for what it is.

What current do you want to charge your packs at?

For instance if you want to charge your packs at 20amps.

The charger you want to use has to charge at 20amps and the power supply you choose has to do the same thing produce 20amps thats it!!!! Of course a few extra amps wont hurt on the power supply side.

getting out the popcorn....
Bubonic-X is offline   Reply With Quote
Old 04-08-2015, 10:49 AM   #17
Tech Prophet
 
Wildcat1971's Avatar
 
Join Date: Apr 2012
Location: Arizona
Posts: 16,985
Trader Rating: 81 (100%+)
Default

Quote:
Originally Posted by Bubonic-X View Post
Everything these guys have said I agree with. BUT......

This the rule of thumb i have always used and has never failed me yet. Of course somebody will disagree bit o well take it for what it is.

What current do you want to charge your packs at?

For instance if you want to charge your packs at 20amps.

The charger you want to use has to charge at 20amps and the power supply you choose has to do the same thing produce 20amps thats it!!!! Of course a few extra amps wont hurt on the power supply side.

getting out the popcorn....
both have to have the watts. dont be fooled by amps. I have a hitec 550watt 30amp power supply that is 18v. I was charging 2 packs at once at 28amps each, for a 56amp load. 56x8.4= 470 watts.

Again, if a charger says 300 watt @ >= 24v, you will not get 300 watts of power from the charger at 12v. Watts takes into account the batteries voltage (1s,2s,3s...). Maybe you dont need 300 watts. 300 watts on a 2s is a lot of power 300/8.4=35.7 maximun, if the software even allows you to go that high. often they put in an "amp" hard limit in the software. But, 300/16.8v (4s) = 17.8amps. So that 20amp icharger could charge both 2s and 4s packs at 17amps with a 300 power supply at 18v output and a 300+ watt rating. But because the software hard limits a 20amp charge, you will never use all 300watts on a 2s charge. 20x8.4 = 168watts of power used to charge a 2s at 20 amps.
__________________
Support: Team Associated | Reedy Motors & ESC's | Sanwa Radios | Avid | Proline Tires
Wildcat1971 is offline   Reply With Quote
Old 04-08-2015, 02:43 PM   #18
Tech Master
 
Join Date: Jan 2006
Location: El Mirage, AZ, USA
Posts: 1,320
Trader Rating: 4 (100%+)
Default

been racing 30 plus years and I have never blown anything or got less charging power than I expected with that rule of thumb.
Leigh you crack me up your such a techy
Bubonic-X is offline   Reply With Quote
Old 04-08-2015, 02:48 PM   #19
Tech Fanatic
 
Orion_2kTC's Avatar
 
Join Date: Sep 2010
Location: Lincoln, NE
Posts: 893
Trader Rating: 9 (100%+)
Default

Get this and you'll have more power than you'll ever need at a cheap price. http://www.ebay.com/usr/strickproduc...p2047675.l2559
Orion_2kTC is offline   Reply With Quote
Old 04-08-2015, 02:56 PM   #20
Tech Prophet
 
Wildcat1971's Avatar
 
Join Date: Apr 2012
Location: Arizona
Posts: 16,985
Trader Rating: 81 (100%+)
Default

Quote:
Originally Posted by Orion_2kTC View Post
Get this and you'll have more power than you'll ever need at a cheap price. http://www.ebay.com/usr/strickproduc...p2047675.l2559
that is just a converted DPS1200. I can buy and convert those for like $35
__________________
Support: Team Associated | Reedy Motors & ESC's | Sanwa Radios | Avid | Proline Tires
Wildcat1971 is offline   Reply With Quote
Old 04-08-2015, 03:00 PM   #21
Tech Fanatic
 
Orion_2kTC's Avatar
 
Join Date: Sep 2010
Location: Lincoln, NE
Posts: 893
Trader Rating: 9 (100%+)
Default

Quote:
Originally Posted by Wildcat1971 View Post
that is just a converted DPS1200. I can buy and convert those for like $35
Fair enough. Working with computers and volatile cheap power supplies my entire working life I didn't have the confidence to mod one myself.
Orion_2kTC is offline   Reply With Quote
Old 04-08-2015, 03:00 PM   #22
Tech Prophet
 
Wildcat1971's Avatar
 
Join Date: Apr 2012
Location: Arizona
Posts: 16,985
Trader Rating: 81 (100%+)
Default

Quote:
Originally Posted by Bubonic-X View Post
been racing 30 plus years and I have never blown anything or got less charging power than I expected with that rule of thumb.
Leigh you crack me up your such a techy
Well, I ran into the issue before. bought a charger, then bought a 12-13.8v power supply and realized I can not get full power out of the charger. I never noticed the wattage rating at a given voltage. And come companies dont even list it on the site, you have to dig through the manual. trial and error and a bunch of research. It seems that most modern chargers are "maximized" for 18-24v. But, for 2s charging it is really not much of an issue. Since it low power. you were a 12th scale guy, lol. Why would you ever need a lot of watts for 1s/4 numh charging. But with todays ebuggy and 4s/6s batteries, it does come into play.
__________________
Support: Team Associated | Reedy Motors & ESC's | Sanwa Radios | Avid | Proline Tires
Wildcat1971 is offline   Reply With Quote
Old 04-08-2015, 03:02 PM   #23
Tech Prophet
 
Wildcat1971's Avatar
 
Join Date: Apr 2012
Location: Arizona
Posts: 16,985
Trader Rating: 81 (100%+)
Default

Quote:
Originally Posted by Orion_2kTC View Post
Fair enough. Working with computers and volatile cheap power supplies my entire working life I didn't have the confidence to mod one myself.
I concur, I use a converted DPS1200 that I did up myself and a few for friends, lol. That power supply is in use by more the 70% of the racers locally and pretty much every stock driver in the main. Even the local hobby shops are selling dps1200's with wraps on them now.
__________________
Support: Team Associated | Reedy Motors & ESC's | Sanwa Radios | Avid | Proline Tires
Wildcat1971 is offline   Reply With Quote
Old 04-08-2015, 03:47 PM   #24
Tech Elite
 
howardcano's Avatar
 
Join Date: Jan 2012
Location: Olathe, KS
Posts: 3,609
Trader Rating: 35 (100%+)
Default

Quote:
Originally Posted by Bubonic-X View Post
Everything these guys have said I agree with. BUT......

This the rule of thumb i have always used and has never failed me yet. Of course somebody will disagree bit o well take it for what it is.

What current do you want to charge your packs at?

For instance if you want to charge your packs at 20amps.

The charger you want to use has to charge at 20amps and the power supply you choose has to do the same thing produce 20amps thats it!!!! Of course a few extra amps wont hurt on the power supply side.

getting out the popcorn....
That's a safe rule if the battery voltage is substantially less than the power supply voltage. If the battery voltage is higher than the power supply voltage, then you need to do the power calculation in watts, and add a safety factor (30% or so extra), just like racer1812 mentioned at the start of the thread.
__________________
Howard Cano
When race results are re-calculated using the IOF (Index Of Fun), I always win.
1993 ROAR 1/8 Pan National Champion
howardcano is offline   Reply With Quote
Old 04-08-2015, 09:28 PM   #25
Tech Master
 
Join Date: Jan 2006
Location: El Mirage, AZ, USA
Posts: 1,320
Trader Rating: 4 (100%+)
Default

Quote:
Originally Posted by howardcano View Post
That's a safe rule if the battery voltage is substantially less than the power supply voltage. If the battery voltage is higher than the power supply voltage, then you need to do the power calculation in watts, and add a safety factor (30% or so extra), just like racer1812 mentioned at the start of the thread.
Now I'm really asking this question cause I dont know.... All of our equipment for racing has and will always be based on a 12 volt power DC. Back in the 80's we carried 12 volt car batteries wherever we raced or charged off the car battery whenever we could Park close to the track and had no AC.
The chargers themselves were always based on 12 volts and to this day has never changed.
That is the constant and the other constant back then was that a car battery could produce any current you needed. And of course the other constant is that we are talking about 2s packs.
Why does everybody bring 12 volts up when we know that is the constant?

Isnt how I think about it just easier then doing all these calculations? You want to charge at 6amps max then you get a power supply that will give you 6 amps or more depending on what you can afford. More current more money. Simple
Bubonic-X is offline   Reply With Quote
Old 04-08-2015, 09:46 PM   #26
Tech Prophet
 
Wildcat1971's Avatar
 
Join Date: Apr 2012
Location: Arizona
Posts: 16,985
Trader Rating: 81 (100%+)
Default

Quote:
Originally Posted by PFKAOG View Post
and another dps1200. see how popular they are
__________________
Support: Team Associated | Reedy Motors & ESC's | Sanwa Radios | Avid | Proline Tires
Wildcat1971 is offline   Reply With Quote
Old 04-09-2015, 12:31 AM   #27
MT4
Tech Initiate
 
Join Date: Dec 2012
Location: Singapore
Posts: 22
Default

I just started using two DPS1200FBA too

Is it normal that it gets hot, yes it's hot, not warm.

Just started on it for storage charging only for 2s, 3s, 4s lipo, individually. Start voltage on each cell was around 3.80v, end at 3.85v.

Psu was set on 12v & 24v, both time was hot. With iCharger 4010 Duo.

I could fry an egg on it

Last edited by MT4; 04-09-2015 at 02:14 AM.
MT4 is offline   Reply With Quote
Old 04-09-2015, 12:59 AM   #28
Tech Elite
R/C Tech Elite Subscriber
 
Join Date: Feb 2012
Posts: 3,347
Trader Rating: 114 (100%+)
Default

http://www.ebay.com/itm/221585175365

Best power supply, I use it to charge 8 2s 5000mah lipos at one time.
__________________
RULE #1 HE WHO HAS THE LOWEST FEEDBACK SHIPS FIRST
RULE #2 ALWAYS FOLLOW RULE #1
2016 Child Truck Giveaway! Click here for details!
http://www.rctech.net/forum/r-c-item...ters-here.html
Seether is offline   Reply With Quote
Old 04-09-2015, 01:02 AM   #29
Tech Elite
R/C Tech Elite Subscriber
 
Join Date: Feb 2012
Posts: 3,347
Trader Rating: 114 (100%+)
Default

Mt4 it should not be that hot, I keep mine in a non ventilation Ted box built into my trailer counter top and its lukewarm at best, charging 8 2s lipos
__________________
RULE #1 HE WHO HAS THE LOWEST FEEDBACK SHIPS FIRST
RULE #2 ALWAYS FOLLOW RULE #1
2016 Child Truck Giveaway! Click here for details!
http://www.rctech.net/forum/r-c-item...ters-here.html
Seether is offline   Reply With Quote
Old 04-09-2015, 05:07 AM   #30
Super Moderator
R/C Tech Elite Subscriber
 
Join Date: Oct 2007
Location: Rochester Hills Michigan
Posts: 7,232
Default

Quote:
Originally Posted by Bubonic-X View Post
Now I'm really asking this question cause I dont know.... All of our equipment for racing has and will always be based on a 12 volt power DC. Back in the 80's we carried 12 volt car batteries wherever we raced or charged off the car battery whenever we could Park close to the track and had no AC.
The chargers themselves were always based on 12 volts and to this day has never changed.
That is the constant and the other constant back then was that a car battery could produce any current you needed. And of course the other constant is that we are talking about 2s packs.
Why does everybody bring 12 volts up when we know that is the constant?

Isnt how I think about it just easier then doing all these calculations? You want to charge at 6amps max then you get a power supply that will give you 6 amps or more depending on what you can afford. More current more money. Simple
The key is the voltage of the pack being charged as Howard and several others has mentioned. Not everybody uses a 2S pack. For the ebuggies running 4S (or more) packs additional power supply current is needed to achieve the power required at the higher voltage. While the 1S guys need far less power supply current.

It's similar to all the threads asking why a common 50 Watt / 6 Amp changer will only go to about 3 Amps on a 4S pack. Not enough power. Yet the current draw from the power supply is about the same in both cases, 2S at 6A compared to 4S at 3A, despite the change in charge current.

With many of the higher powered chargers available a higher voltage supply is needed for the larger packs at high charge currents, due to charger input current limitations. It's far easier, cheaper, and more efficient to use higher voltage to achieve the high power levels.

In the '80s chargers like this Tekin BC100L were common. It came with a large power resistor to reduce the supply voltage when charging 1/12 scale 4 cell nickel packs, or a 10V or slightly lower power supply could be used (typically an adjustable voltage power supply). To prevent burning up the charger when charging these lower voltage packs. On the other hand it was simply not capable of charging a 12 cell pack with a 12V supply. Modern switch mode chargers have certainly increased the flexibility of chargers, but haven't altered the power relationships involved.


Last edited by Dave H; 04-09-2015 at 05:33 AM.
Dave H is offline   Reply With Quote
Reply


Tags
ac/dc, charger, power supply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 02:54 PM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net