balancer harness

[jefierro]

Greetings first post here.

I want to build a Y harness that will charge and balance two 2s lipos at the same time like if there where a single 4s battery, I have a Triton2 charger and the equinox cell balancer. just want to double check this first just to be safe and don't end up burning up my house.

this is the harness adapter i want to build


this is the original 4s adapter


thanks.

Originally Posted by jefierro

Greetings first post here.

I want to build a Y harness that will charge and balance two 2s lipos at the same time like if there where a single 4s battery, I have a Triton2 charger and the equinox cell balancer. just want to double check this first just to be safe and don't end up burning up my house.

this is the harness adapter i want to build


this is the original 4s adapter


thanks.

here is a link to a recent post, hope it helps

http://www.rc-monster.com/forum/show...263#post157263

[BrianG]

Using two seperate balancers is not a good idea IMO because a balancer works by discharging high cell(s) in a pack. It works off the relative voltage levels, not some absolute value. So, if two cells on one pack were at 3.7v-3.7v, and the other two in the other pack were at 3.5v-3.5v, each pair would be balanced, but not to each other. The only way this works if there is a way for the balancers to talk to each other, like in the LBA balancers.

However, you can use the 4s single unit balancer. From the picture you posted, I think it should be hooked like this:

[jefierro]

Sorry I should have explained my self a bit more earlier, the green boards are not balancers just balancer tabs connectors, Align/Equinox type if you must, not the same as the Hyperion tabs. The withe tab in my image connects directly to the equinox balancer, and this is the only link for the batteries to the charger. these adapters and balancer are rated up to 6 amps using both the main lead and balancer connectors.
my lipos are two maxamps 2s 5000mAh with align/equinox tabs (3 pins)

This adapter, so I intend it to be, a solution to charge and balance two 2s lipos as one 4s lipo at 1C(5amps) so the use of the main leads and the balancer tabs are needed to distribute the current over more wiring to eliminate heat at the connectors. Hope this will explain my intentions.


thanks all.

[BrianG]

I think I understand now.

However, in order to charge through the balance taps at 1C, I would use larger gauge balance wires (~18GA) and use better connectors... something like those multi-pin Deans or something like that. Otherwise, there will be too much voltage drop on the connector and/or the wires under the higher charge currents and the balancer might not function correctly. This is why charging through the main leads and balance off the taps works so well.

[jefierro]

The First time I tried to charge one lipo i didn't had the "High Current adapters" so I try to charge them only thru the balancer tabs, the Triton2 only charges at 1C no more and no less, so the connector promptly started to get hot. after no more than 2 min i had to disconnect them as the connectors where to hot. Now i have several "high current adapters" but the wiring is thin don't know the GA but are same wires as the second image in my first post but these do not develop heat as they use both main lead and balancing tabs, I temp them and where only 2 to 5°F above ambient. I Charge and balance each battery in ~80min. The triton2 gradually drops current after 80% charge so peak takes much longer.

do you think I'm having drop voltage at the connectors and/or thin wiring? should i expect similar temps or voltage drop in the proposed adapter? or should i jump of a bridge and stop asking silly questions?

[BrianG]

lol, there are no silly questions... well, there are, but we won't go there. So, no need to jump off any bridges...

Anyway, high temps on a connector and/or wire means there is a voltage drop. The amount of drop depends on the current flow and the resistance of the connector/wire. This voltage drop means the balancer will see less voltage than there actually is on the cell and may balance according to that erroneous reading.

Hot connectors are obviously bad and should be replaced with something with less contact resistance. Mini power-poles, mini-deans, etc can work - whatever you use, you probably want something physically small. Even though wires don't get hot, they could also be dropping voltage, but because they are fairly long, the resulting heat could be being wicked away. You could measure the drop with a meter (measure the voltage at the extreme ends of the wire). Remember, balancers are trying to maintain cell balance to around 0.05v, so ANY voltage loss can trick the balancers.

That said, if you want to charge and balance through the taps and don't want to replace all the wiring, I would make those balancer wires as short as possible. Wire has X amount of resistance per foot. So, it stands to reason that if the wire is shorter, there is less resistance.

So, go with good connectors that offer low contact resistance and at least 7-10A rating (higher is better even if you don't charge that high) and keep wires short.

Oh, since the charger charges at 1C no matter what, you can probably trick the charger into charging at lower rates by telling it that you are charging a lower capacity pack. So, if you want to charge a 2000mAh pack at 1A, set the capacity to 1000mAh. Just be aware that this will take twice as long and the charger may have a safety timer built-in to terminate the charge after X amount of minutes...

[jefierro]

Thanks that was most illuminating. other than voltage drop is this adapter doable? as the connectors are mostly fixed, I have Traxxas high current connectors and the tab that is used for the equinox balancer, the only ones I can change are the ones that connect the balancer tabs, surly those boards can take 5amps!?? or not?

I still have my doubts about the second red wire linking the two batteries at the balancer tabs. I don't know how goes the internal wiring of the balancer so i don't know if it's needed or not.