K2 vs. StarkPower LiFePo4 batteries

Here is my e-mail conversation with the TechRep at K2.


I want to wire two 12v10aH K2 batteries in a parallel circuit to yield a 12v20aH pack. Is this acceptable? Will a single K2 charger charge both batteries simultaneously?

Great product!

Thanks, Mark



Yes, you can wire them in parallel and still use our charger to charge them up. Note, if you are dealing with high amperage, the parallel wiring doesn't mean double the max amperage.


Best Regards,

Mark Stoker

K2 Energy Solutions, Inc.

On Tuesday, April 14, 2015 at 11:53:31 PM UTC-4, wrote:
Here is my e-mail conversation with the TechRep at K2.


I want to wire two 12v10aH K2 batteries in a parallel circuit to yield a 12v20aH pack. Is this acceptable? Will a single K2 charger charge both batteries simultaneously?

Great product!

Thanks, Mark



Yes, you can wire them in parallel and still use our charger to charge them up. Note, if you are dealing with high amperage, the parallel wiring doesn't mean double the max amperage.


Best Regards,

Mark Stoker

K2 Energy Solutions, Inc.

Running 2 batteries always connected in parallel is/can be a bit different than having 2 batteries charged off a single charger in parallel.
A lot comes down to the state of charge in each battery when you start charging them as well as what (if any) circuitry is inside the battery.

"DC doesn't switch worth a crap either... interrupting a high current DC load is *really* hard on switch contacts and best avoided."

Better to get rid of switch entirely and just install a diode for each battery?

On Wednesday, April 15, 2015 at 1:03:37 PM UTC-4, Clay wrote:
"DC doesn't switch worth a crap either... interrupting a high current DC load is *really* hard on switch contacts and best avoided."

Better to get rid of switch entirely and just install a diode for each battery?

With diodes on each master circuit, you prevent back-feeding the discharged battery and the high current problem goes away. Keep the switches.

best,
Evan

I have two LiFePO4 batteries and two toggle switches. When it's time to
switch I simply turn on the second switch and turn off the first.
Click, click - it takes about as long to do it as to say, "click,
click". No problems.

On 4/14/2015 6:41 PM, Tango Eight wrote:
On Tuesday, April 14, 2015 at 8:23:29 PM UTC-4, Ron Gleason wrote:
On Tuesday, 14 April 2015 17:44:48 UTC-6, Tango Eight wrote:
On Tuesday, April 14, 2015 at 7:29:58 PM UTC-4, JS wrote:
I have used and charged two 10AH LiFePO4 batteries in parallel sans probleme.
Jim

On Tuesday, April 14, 2015 at 2:48:04 PM UTC-7, Ramy wrote:
Can one charger charge two identical starkpower batteries in parallel?

Ramy
Please take questions of this sort to the manufacturer of *your* batteries. The right answer is going to depend on the details of internal construction. And there are going to be some cautions if not an outright admonishment against this.

LFP batteries have very low internal resistance, so batteries in different states of charge will pass a very large current when connected in parallel until their voltage is equalized. If your batteries are fused as they should be (right on the terminal), you stand a fair chance of blowing fuses if you hook together batteries in reasonably different states of charge.

Here's a *great* time to ignore the "well, it worked for me" replies. It'll work acceptably well right up to when it doesn't.

My $0.02.

Evan Ludeman / T8
Damn you Evan, presenting common sense and logic. I looked on the K2 website and nothing mentioned about charging in parallel. However chargers are $50 buck, cheap insurance.

Not an excuse but this setup came with the plane I acquired. Buyer beware, but I should have checked the setup. yup ordered a second charger today. Thanks Evan.

Ron
No trouble!

So the next consideration is switching in flight. Same concerns apply...

I've never been able to figure out a good way to get a back up battery in my 20, so I have just one big honking 12AH battery. But if I had a dual LFP battery system, I'd use (appropriately rated) low voltage drop diodes to prevent back feeding the low battery with some mongo current during switchover. With my luck, I'd blow the fuse on my good battery....

-Evan / T8

--
Dan Marotta

On Wednesday, April 15, 2015 at 4:21:29 PM UTC-4, Dan Marotta wrote:
I have two LiFePO4 batteries and two toggle switches.* When it's
time to switch I simply turn on the second switch and turn off the
first.* Click, click - it takes about as long to do it as to say,
"click, click".* No problems.


Run your first battery down to 11.5 V, then put an ammeter in line and let us know what the surge looks like when you switch in the second battery (at full capacity). I'm genuinely curious.

-Evan

All commercially available "SLA replacement" LiFePO4 batteries have overcharge and over-discharge protection.
From my experience, if run in parallel they will have the same voltage. After a typical 5-hour flight with a full panel running, about 12V.
Charging two similarly discharged batteries in parallel worked well, but the chargers I was using at the time didn't quite have the voltage required for LiFePO4. I now use separate chargers that came with the batteries from Tenergy.
But underneath the workbench the glider batteries charge on, there's a bank of eight AGM batteries running the inverter/UPS on the entire house. They're running at 48V in series/parallel, under constant charge and discharge.
Adding a diode to your batteries will prevent your Strobl Solar system from charging them in flight. Discovered the solar panels unnecessary with LiFePO4.
Jim