Dual A123's, Power Expanders, and Charging

[Sin City Jets]

I have been getting a lot of questions about "I heard you can't charge two batteries if you have a power expander while they're hooked up."

I checked with the people that actually know what they're talking about (unfortunately I'm not one of them) and I wanted to pass the answer on. So the answer is.....simple but complicated, but here goes:

There are two types of chargers...."High" side and "Low" side. A HIGH side charger keeps track of how much energy it is putting in to the battery via the POSITIVE lead. A LOW side charger keeps track of how much energy it is putting in to the battery via the NEGATIVE lead......so, with that in mind, IF you have a HIGH side charger, you CAN charge both battery packs at the same time, even if they are connected to the power expander. If you have a LOW side charger, you CAN NOT charge both packs, at the same time, while they are both connected to the power expander.

Now, IF you do have a LOW side charger, you still have a couple of choices:

1. Charge only one battery at a time. If you only charge one battery at a time, you CAN charge the battery even if both are connected to the power expander.

2. Disconnect one (or both) connectors from the power expander. If one of the batteries is disconnected from the power expander, you CAN charge them both at the same time.

Now, you are probably wondering, how can I tell if I have a high or low side charger....good question. Chances are, the place you bought it from, and even the manufacturer may not know (unles you get a technician). So, with that in mind, better safe than sorry.

FINAL WORD: You WILL ruin your charger and battery if you charge two batteries at the same time while connected to any power expander IF it is a LOW side charger. Charge them one at a time, or disconnect one battery from the expander.

I hope that clears it up for some.

PS this is true for all batteries, not just A123's. I just like putting A123 in the title

[crazyjoe]

I just had that very conversation with someone at smartfly
I have to a123s into power expander pro w/failsafe switch
I called cellpro and tried to find out how their charger operated but wasn't able to explain the high side low side deal to the tech so he couldn't tell me how his charger worked he just told me to disconnect one bat.
One of the benefits of using a123s is being able to quick charge at the field in between flights but taking the canopy of to charge is a pain in the rear
So if anyone out there with more electrical knowledge could find out which way the cellpro 4 charges that would be great

[DKjens]

	Quote: Originally Posted by Sin City Jets
	FINAL WORD: You WILL ruin your charger and battery if you charge two batteries at the same time while connected to any power expander IF it is a high side charger. Charge them one at a time, or disconnect one battery from the expander.

Here you mean if you have a LOW side charger, right, not a HIGH side charger?

[psk560]

How will charging through the powerexpander ruin it? If you are charging with a current that the unit can handle won't that be ok? Won't a y-harness put the packs in parallel (Which they are anyways when you use two packs). The parallel cicuit will allow a charger to charge the packs. Balancing is a different story.

Craig

NOTE: try at your own risk. Use a multimeter to measure current and voltages!

[Rolling Thunder]

The batteies share a common ground. Some chargers do not work with a common ground. I use my old Powerflight, fromeco, and TP 1010c chargers through the power expander with no problem.

My buddy has the hobbico quick field2 charger and he can't charge both bats at the same time.

[psk560]

Even when put in parallel?

I used the cellpro and y-harness to charge my packs. I measured the current that went through the ground wire through the recievers and I didn't measure a current. That must mean it charges through the positive lead. Is that correct? A high charger?

Craig

NOTE: try at your own risk. Use a multimeter to measure current and voltages!

[bodywerks]

Using a power expander is nothing like using a Y-harness. You are not paralleling two batteries. If you parallel batteries, you run the risk of power failure if one battery goes dead or shorts out, because the other battery will either feed the dead battery or fail as well if there is a short. With a power expander, both batteries only supply power if they are within 0.2 volts (or is is 0.02?) of each other. If one drops out of range, then you only get power from the higher voltage battery, until they equalize again.
Still, I think all this hooplah about dual charging is if you balance charge, which is TOTALLY unnecessary - regular charging should still be OK, but I haven't tried it myself yet...

[Rolling Thunder]

There are some chargers that will not work with a common ground system when charging 2 batteries. The Hobbico field charger II is one of them.

[Sin City Jets]

	Quote: Originally Posted by DKjens
	Here you mean if you have a LOW side charger, right, not a HIGH side charger?

Good catch DK. Here I was trying to do a good deed and almost screwed everyone up!!

The post has been corrected!

[crazyjoe]

So does anyone know if the cellpro 4 which most people are using to charge a123s is a high or low charger

[Sin City Jets]

Unfortunately....no (at least I don't)

[Pale Rider]

	Quote: Originally Posted by crazyjoe
	So does anyone know if the cellpro 4 which most people are using to charge a123s is a high or low charger

Not sure if this is what you are asking but the Cellpro4 charges at 4A