LRP SPX8 question

[sime46]

I have one of these and am very happy so far. My question is, although the manual says the BEC needs 7.4v, would 6v work? I've bought a 4s pack and was gonna plug the BEC into the reciever to give it a 6v supply to the speedo BEC. Otherwise the manual suggests picking my feed up from the balance plug on my 4s pack. Any help greatly appreciated. Cheers.

[Marvin]

No, I think it means 2S input max, for 6V output. Remember, the BEC can only take 2S, so if you're looking to run more than 7.4V then you'll need a separate BEC or a Rx pack.

[ojoloco]

I'm guessing it's 7.4v min, since the ESC is intended for 2-4S and all the info i could get about it didn't mention anything about external BEC's required.

Little off-topic, LRP SPX8 combo is light! I saved 123 grams from the MMM-2200Kv to the RX8-1900Kv, but this is even lighter! 100g less than the Tekin...I would be under 3000g now if i had the LRP...


PS: Yes, i'm a lightweight freak

[Tyson]

I have the SPX8 fitted in to my HB Ve8, If you run 2 normal stick packs to make 4s your ok. I do this using 2x Trakpower Dark 5000mAh 40c batteries.

There is a wire coming from the SPX8 with a switch that connects to the bridge wire between the 2 stick packs. Because you are taking a negative referance then the switch wire coming from the bridge wire is 7.4v.

When the system is connected in this way it does not unbalance either of the 2s packs (LRP designed it to work this way), if you are using a proper 4s single pack then it is not recommended that you connect the SPX8 to the balance port as it will unbalance the 4s pack, due to the reciever and all its devices draining one cell of the 4s pack unevenly.

Hope this explanation makes sence

You are right with the weight and size of this speedo, its so small it allowed me to make the HB Ve8 into a saddle pack like the caster. This turns it from a cool car to an awesome perfectly balanced car

[Marvin]

What? Yeah right, discharging one pack quicker than the other doesn't unbalance them, right on...

Also, that's a bit useless for anyone not using two stick packs. 7.4V max is rubbish - that's one of the reasons it's so light. By the time you add a BEC, it's not so light anymore, and you're limited to 4S max, unlike the Tekin, 150A Hobbywing, Losi and MMM, which don't need a separate BEC, and can run 6S (aside from the Losi, which'll do 5S).

[Tyson]

Perhaps i didnt explain right, tried to make it as simple as possible this time!

Connecting the BEC input wire from the SPX8 directly inbetween 2 saddle stick packs (4s) is apperently the best method as LRP only make stick packs no more than 2s. (They designed it around there product line not a 3rd party battery supplier)

The MANUAL states that if a single 3s or 4s battery is used, then you must correctly identify the the right pin on the balance plug of the 3 or 4s battery.
(This means that you are taking the supply voltage and current drain from particular CELLS within a 3 or 4s pack which also combined with other CELLS in the PACK supply the ESC)

*Perhaps this current drain from powering the RX, PT and servo on particular CELLS within a 3 or 4s PACK, could posibly leave those CELLS within the PACK at different voltages? i.e UNBALANCED CELLS in a PACK*

*Perhaps it might be better, if you use an external BEC when connecting a single 3 or 4s battery pack with the LRP SPX system?*

*IMO

I am also not telling anyone to go buy this system because it is better than MMM, Tekin, Losi etc, i was explaining the operation as dictated by the manual supplied with the SPX8. (I just own one)