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Old Aug 27, 2010, 08:24 AM
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Crawley Down, UK
Joined Mar 2005
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Dual A123 charging with single rx (common ground)?

Just moving up from 50cc models to 100cc models and I am going to use dual A123 packs now. Currently use a Cellpro Multi 4S as my charger and this has served me well with my current setups using a single A123 pack.

My setup with use dual A123's connected via a dual mechanical switch to a single Futaba 6014 rx with an Orbit Powerjack. The dual switch has dual charge ports so I planned to connect the balance leads of the the A123 to these.

My question is can I charge one pack at a time with the Multi 4S without having to open the model up and disconnecting one of the pack from the rx?

I understand that I can now use two Multi 4's and they will overcome the common ground issue but will one charge one pack at a time?
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Old Feb 01, 2011, 02:43 AM
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Common Ground

Did you ever get an answer to this?

I'm not a rocket surgeon and am trying to understand the common ground phenomena. It seems there is common ground issue with the scenario you are asking about which is charging two batteries with two chargers while connected to a receiver, and there is a common ground issue related to the power supply while charging two batteries.

I'm sifting through some posts reading as much as I can on it.

In this post http://www.rcgroups.com/forums/showthread.php?t=298802 it says the following;

Quote:
"common ground" is only an issue if you are attempting to charge individual cells in a series-connected battery (common in LiPo) - in which case, you'll end up shorting cells. Otherwise, it makes no difference running multiple chargers off one power supply. I run three on my 20A PSU..
Does this mean that if the batteries being charged are not using a balance charge that all is well?

Is there a sketch or tutorial somewhere that may be an eye openere for me?

Thanks for any ideas
Bob
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Old Feb 01, 2011, 07:55 AM
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Quote:
Originally Posted by andyjayh View Post
Just moving up from 50cc models to 100cc models and I am going to use dual A123 packs now. Currently use a Cellpro Multi 4S as my charger and this has served me well with my current setups using a single A123 pack.

My setup with use dual A123's connected via a dual mechanical switch to a single Futaba 6014 rx with an Orbit Powerjack. The dual switch has dual charge ports so I planned to connect the balance leads of the the A123 to these.

My question is can I charge one pack at a time with the Multi 4S without having to open the model up and disconnecting one of the pack from the rx?

I understand that I can now use two Multi 4's and they will overcome the common ground issue but will one charge one pack at a time?
Hi,

The Multi 4 chargers will still have a problem with common ground issues and you should not attempt to charge this way as it can damage your charger. You must break the common ground (negative wire) in order to charge multiple packs with multiple chargers.
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Old Feb 01, 2011, 09:28 AM
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Thanks Howard

I'll take your advice, and keep reading so I better understand in my mind what's going on and why.

Take care
Bob
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Old Feb 01, 2011, 10:38 AM
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Quote:
Originally Posted by Howard Matos View Post
Hi,

The Multi 4 chargers will still have a problem with common ground issues and you should not attempt to charge this way as it can damage your charger. You must break the common ground (negative wire) in order to charge multiple packs with multiple chargers.
Okay now I'm confused but I cannot locate the thread/picture....

I've had a number of exchanges with you folks about the common ground issue starting with my 10S and understand what the problem is, but in the course of those exchanges I seem to remember you posting different information about the Multi-4?

IIRC, you indicated at some point in the past that a pair of Multi-4 chargers could be used at the same time on two packs having a common ground (through the rx buss) with no problem? It seems like I remember a picture you posted of that setup on a bench? It is possible I saw that on another forum, but I was thinking it was this forum. It is also possible it was posted in a thread related to the 10S rather than the Multi-4 but I've scanned through the threads here to no avail.
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Old Feb 01, 2011, 02:35 PM
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http://www.rcgroups.com/forums/showt...3#post11834754
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Old Feb 01, 2011, 03:08 PM
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Hi:

It is true we posted information in the link Steve supplies. But later, we discovered there are still problems with this scheme. Sorry, we have to retract this old information.
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Old Feb 01, 2011, 03:32 PM
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Howard, good to know which one of you to trust.
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Old Feb 01, 2011, 05:34 PM
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Common

Does the Multi 4 statement carry through the entire line of chargers, 10S thru Powerlab 8?

Thanks
Bob
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Old Feb 01, 2011, 07:41 PM
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The Multi4 was the only one that was advertised (in a very limited fashion) to have this feature so I doubt any support it. Remember, you can still charge batteries with a common ground as long as the two chargers are powered from different sources (eg. two different lead acid batteries or one on a battery and one from an AC to DC power supply).
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Old Feb 02, 2011, 10:21 AM
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Quote:
Originally Posted by SteveM732 View Post
The Multi4 was the only one that was advertised (in a very limited fashion) to have this feature so I doubt any support it. Remember, you can still charge batteries with a common ground as long as the two chargers are powered from different sources (eg. two different lead acid batteries or one on a battery and one from an AC to DC power supply).
Hmmm.....

Wasn't aware of that but it's kind of interesting. I won't be pursuing that option since I tend to just use my 10S off a deep cycle 12V battery at the field. I do have a Multi-4 as well, but since all my models are on A123's the only time I charge batteries with very few exceptions is at the field and I'm not 'gonna be lugging two big batteries to the field with me.... lol

Thanks for the clarification Howard, but is there any chance we can get this common ground issue addressed somewhere down the road?
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Old Feb 04, 2011, 09:08 PM
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I balance charge two A123 with my Cellpro 4S at the same time by doing then in parallel..
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Old Feb 04, 2011, 09:15 PM
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Common

I find Steve's comment interesting as well.
In post #7 in the link below, Bob Ritchey from Smart Fly has this to say ->


http://www.flyinggiants.com/forums/s...ad.php?t=25739

Quote:
The common ground problem has been around a very long time, anyone that has ever used two batteries with a receiver has run into this. We did not feel it was necessary to hit people over the head with warnings. Most people "should" be familiar with it now. You CAN charge one battery at a time even with both batteries connected. You CANNOT charge both batteries at once with a single dual-output charger or two separate chargers if they cannot handle the common ground system. These are rules. I can get technical on why these are the rules if you like. Let me know.
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Old Jan 18, 2012, 04:40 PM
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Originally Posted by Howard Matos View Post
Hi:

It is true we posted information in the link Steve supplies. But later, we discovered there are still problems with this scheme. Sorry, we have to retract this old information.
Hate to dig up a thread this old but the question remains. I remember Howard posting this:

http://www.rcgroups.com/forums/showt...3#post11834754

I didn't remember the later retraction:

http://www.rcgroups.com/forums/showp...94&postcount=7

So not thinking about the retraction I got a second Multi 4 the other day with the idea of using two of those instead my 10S. After a discussion over on FG, someone pointed out the issue with using a common power supply so I came back here looking and found the retraction. The responses in this thread don't seem to indicate if you can use two chargers with separate power supplies?

Other question is that I spent quite a bit of time both on the phone and e-mails with one of your engineers when the 10S was about to be released. He told me that it was possible to have a software solution to the common ground issue but that there was not enough memory in the 10S to include that programming. So.... can the issue be addressed with software? If so, what about an update so the Multi 4's could do it?

Thanks in advance Howard!
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Old Jan 18, 2012, 07:43 PM
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Quote:
Originally Posted by Zeeb View Post
Hate to dig up a thread this old but the question remains. I remember Howard posting this:

http://www.rcgroups.com/forums/showt...3#post11834754

I didn't remember the later retraction:

http://www.rcgroups.com/forums/showp...94&postcount=7

So not thinking about the retraction I got a second Multi 4 the other day with the idea of using two of those instead my 10S. After a discussion over on FG, someone pointed out the issue with using a common power supply so I came back here looking and found the retraction. The responses in this thread don't seem to indicate if you can use two chargers with separate power supplies?

Other question is that I spent quite a bit of time both on the phone and e-mails with one of your engineers when the 10S was about to be released. He told me that it was possible to have a software solution to the common ground issue but that there was not enough memory in the 10S to include that programming. So.... can the issue be addressed with software? If so, what about an update so the Multi 4's could do it?

Thanks in advance Howard!
Hi:

You can charge 2 common-ground connected packs across 2 Multi4 provided that the PSU's are isolated. You must be careful and you must do this correctly, or you could have a bad situation on your hands. You have to check for continuity between the PSU negative outputs. If there's continuity, don't do it. For many PSU's, there exists common ground because the DC outputs are connected to the AC ground.

If you attempt this with a Multi4 and a single PSU, or 2 PSU's that are NOT isolated, the only thing it buys you is that the chargers should not be damaged.

There is no software solution available for this. We thought we had it when we announced the Multi4 could do it, but further testing revealed there were problems we forgot to consider.

There is a sticky at the top of the FMA forum which covers the same things I've mentioned above. Check the thread:

http://www.rcgroups.com/forums/showthread.php?t=1122223

I just updated the links a week or so ago. This sticky is based on 2 packs connected in series, but similar problem for 2 packs with common ground, so it still applies.

Tim Marks
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