Thanks Oli for the new thread.

In the other thread I've been recommending the JR/Spektrum powersafe RXs. They have dual battery inputs with large gauge wire and heavy duty connectors to bring the power to the RX. They also have circuitry that works to draw down the two batteries evenly built into the RX and offers some isolation.

I highly recommend the A123 batteries in a parallel setup as well, and agree with the great source of information you listed at Hangtimes hobby/No BS batteries. That whole site is recommended reading. One thing about internal resistance and voltage drop that is important to remember...when using a parallel setup, (two batteries with two separate paths to the RX) the internal resisitance is effectively halved giving you even less voltage drop for the entire system. Another plus to parallel setups.

With the performance of A123/LiFe batteries, the voltage drop under load is very low. There's been some concern in using two 1100mah packs in parallel to give a total capacity of 2200mah. The worry is that if one battery or connection fails, the single 1100mah pack will not be up to the task. By all accounts and data, it will be up to the task, but will not give you multiple flights...so you'd better be doing proper preflight checks to assure that both packs are supplying power to the RX and you haven't had a battery,switch, or connector failure.

With the JR/Spektrum powersafe RXs, you have an indicator light for each battery system that lets you know that both are supplying power to the RX.

The other thing that I try to do is avoid regulators and that's another reason why I dont use Lipos/Lions and have gone to A123/LiFe packs. Regulators are just one more component that can fail and cause trouble. For the same reason I also avoid D cups and other similar items. There's also some small variances in the outputs of regulators, even of the same make and model, that can cause some peculiarities in a parallel system (two batts thru two regs into a powersafe rx). One regulator putting out slightly more voltage than the other battery/regulator combo will supply most of the current to the RX and the batteries will drain unevenly when used with a powersafe RX or other device that tries to balance the two batteries in a parallel setup.

So a parallel system using A123/LiFe batts with no regulators is a great setup. Using a JR/Spektrum powersafe RX with the included softswitch is my choice because it also uses heavy duty wiring and connectors for better current carrying capacity, and removes switches from the power path that increase resistance and are another failure point. It also evens out the drain on the two battery packs and provides some isolation between the pack.

As for capacity, I try for five flights between charges and roughly 40-50% capacity left in the batteries after those five flights. Typically, we are going to use somewhere between 150-400mah per flight depending on the size of the model, number and type of servos, flying speed, and flying style. Using my rule of thumb for capacity, if you only use 200mah per flight that would be 1000mah used for 5 flights. With a 50% reserve capacity left in the batteries we'd therefore want to be carrying at least 2000mah onboard....So two 1100mah packs would be fine. If we were using 400mah per flight, then we'd use 2000mah in five flights and would want 4000mah onboard to have enough reserve. That would suggest that two 2300mah packs would be the ticket.


KMac