Before I get all those "this is simple" replies... let me state once more as I have in other threads. The extent of my knowledge in electricity is that "I know it hurts to pee on the fence" THATS IT! Now... here is what I want to get straight before I burn down the house.... I have four 3.2 vdc 20AH LifPo4's. I need to run them in a mix of parallel and serial runs to get 6.4 vdc 40 AH. I know how to run two batteries in parallel... with parallel; the (-) post of battery "A" is connected to the (-) post of battery "B", then connected to the (-) end of the busbar. The (+) post of battery "A" is connected to the (+) post of battery "B", then connected to the (+) end of the busbar. Thats it.. I have now kept the same voltage, but doubled my AHs. I know how to run two batteries in serial... with serial; the (-) post of battery "A" is connected to the (+) post of battery "B", then (+) post of "B" is connected to the (+) end of the busbar. The (+) post of battery "A" is connected to the (-) post of battery "B", then the (-) post of "B" is connected to the (-) end of the busbar. Thats it.. I have now kept the same AHs, but doubled my Volts. My issue is how to mix these.... there are 3 or 4 ways on the net how to do this so I am not sure. I made a pic of what I think is the best way... is this the correct way, or is it wrong? This should result in a system with 6.4 VDC and 40AH... I think
So it looks like you put two in series and then put two in parallel. I use the same setup though I draw it differently. You could also put two in parallel and then put the two sets in series as well. It looks right to me. However I run each set with its own wiring to the bus bar to optimize the current flow on the wire. I personally wouldn't solder together the positives and negatives of each series pack before attaching to the bus bar. The current will be higher on the single wire attached to the bus bar as compared to having 1 wire per series pack attached. I only know of two ways to wire those cells to get 6V / 40AH and you are doing one of them. Though I would call yours a 2S2P pack. The other method would be 2P2S I guess. And I don't wire my batteries together permanently either.. fyi.. easier to charge single cells.. no balancer needed that way.
Sweet Jeebus! Why'd you change from the first one? It was good and way simpler, and achieved what you wanted Top one above is wired backwards, the + would be -... did that once without meaning to. Quite funny in practice. Second one is wired okay but is complex and uses lots more wire than your original. Go simple
OK, I'm getting a nice 7.4 VDC off of my Lifepo4s. Do I need to drop that voltage a little for the firing boards and receiver? I think the Viper ESC uses a BEC.... will that keep the voltage down to 6vdc for the receiver? I think the boards can handle the 7.4... not too sure though. Who has the Lifepo4s and what do you do for your firing boards?
The ESC should drop it for the RX. some firing boards and RXs are tolerant of 7.4, the majority not so. A suggestion would be to put a diode on each of the serial pairs. this not only drops the voltage (you might want 2 if you really want to drop to 6v or less), but keeps a bad cell on one side from draining the other cell s in parallel. I commonly wire my harnesses that use multiple SLAs with low drop diodes to keep a bad/weak 6v battery from drining the good ones. Haven't had to wire a new harness in several years, though. I have seen someone with a 2 SLA ship charge both his SLAs, plug them in to the harness to test, switch off and unplug the harness (but not from each battery) and have the system weak or dead after o 4 hour drive to the pond. One battery was bad, and the other one died trying valiently to maintain its brother's charge. Cheers, Wreno
I use a separate receiver battery so I don't have to worry about it... 6.0v nimh pack.. no resistors no diodes just plug it in and the firing boards I use work just fine.
Nope. BEC equipped ESCs (which is 99% of the low voltage ESCs on the market) supply enough current to power the receiver.
However: caution. Many ESC's BEC function only deliver up to 1A (some less). Depending on how many servos/elecronic switches you are running off of te RX power directly, you can overwhelm the 1A (more a problem in Big Gun, where we have rotation servos, depression servos, etc.) If you are running a RX battery, you should disconnect the red lead from the ESC, or you may bet a back-power that can fry the EXC under certain conditions. If you are running multiple ESCs, you should disconnect the red wire from all but one. Alternatively, if you have a lot of servo power draw, you can power them separately - an easy way is one of hese:servocity.com/html/servo_power_boards.html Cheers,
Wrenow is on the money there. The 1 amp my ESC provides is not enough so I use an adapter between the ESC and receiver and remove the red pin. I find that some firing boards draw more power than others and I don't want that to be an issue with a rudder servo or anything like that. I prefer not to alter the esc receiver plug for warranty reasons so the adapter works. Just keep the connections clean with corrosion X and then lube it with dialectric grease and you are in good shape.
Most of the HobbyKing ESCs 30A and up provide at least 2A and many 3A. They also sell higher rated dedicated BECs for extreme applications.
The Mtroniks 40 does not like this setup.. I had to take mine out. I have no idea why.. I tested it with 2 cells and it works fine.. 4 cells and it wouldn't work.you lose instant reverse.. it stutters. or doesn't backup at all. I think its trying to sense Lipo or something and as such the voltages are wrong.. I dunno.. Now if the one you have was made in the last few months.. maybe its fixed. Mtroniks tech support never replied to my request for help.. I put the banebots in and it worked fine.
Is this the ESC you use? banebots.com/pc/ELECTRONICS/BB-1245 I have two 550 cans on the Mutt, will the 12amp continous limit be ok?
