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Brown-outs with HV servo directly on 2s Lipo ? Or something else ?

Brown-outs with HV servo directly on 2s Lipo ? Or something else ?

Old 05-12-2013, 01:14 PM
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Default Brown-outs with HV servo directly on 2s Lipo ? Or something else ?

I'm running a HW Sct Pro Esc and 2s battery. I recently installed a Savox 1268 HV servo connected to my Esc (so not running high voltage) and noticed brown-outs, so I figured I'd hook up the servo directly to my lipo to
a) prevent brown-outs and
b) run it on 7.4v.
Tried that, seemed to work fine, now I was running my car again yesterday and I noticed after running for a while sometimes the steering wouldn't react properly again. The battery *was* running kind of low, but it still had enough oomph to power the motor...

To the best of my knowledge (which admittedly isn't very good) a 7000mAh 50C battery should be able to cough up 350 ampere, so to me it seems unlikely to be a brown out.. (?) The throttle was still working fine so the Esc hadn't even gone into LVC yet so I figure there should be enough power left to power the servo and RX as well.
So if it's not a brown out, what else could it be ?
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Old 05-12-2013, 07:46 PM
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Originally Posted by Pygmy
I'm running a HW Sct Pro Esc and 2s battery. I recently installed a Savox 1268 HV servo connected to my Esc (so not running high voltage) and noticed brown-outs, so I figured I'd hook up the servo directly to my lipo to
a) prevent brown-outs and
b) run it on 7.4v.
Tried that, seemed to work fine, now I was running my car again yesterday and I noticed after running for a while sometimes the steering wouldn't react properly again. The battery *was* running kind of low, but it still had enough oomph to power the motor...
Because the car was still capable of driving doesn't mean that there aren't large voltage fluctuations. The fluctuations can be large enough to cause the ESC BEC voltage to fluctuate as well. These cause the receiver to have issues.

Originally Posted by Pygmy
To the best of my knowledge (which admittedly isn't very good) a 7000mAh 50C battery should be able to cough up 350 ampere, so to me it seems unlikely to be a brown out.. (?) The throttle was still working fine so the Esc hadn't even gone into LVC yet so I figure there should be enough power left to power the servo and RX as well.
So if it's not a brown out, what else could it be ?
You're battery is capable of supplying many watts. Even when it's fully charged, the voltage fluctuates though. The thing is, those fluctuations don't get the voltage low enough to cause an issue. The following is from my 1/10 stadium truck with a Novak Pulse ESC and Trinity 3800kv motor. Take note of how large the fluctuations are. The ESC's BEC helps to flatten this out as they normally regulate to 6 volts. As I stated earlier though, when the voltage get's low, the BEC suffers as well. I can't seem to find the BEC graph I thought I had, so I can't display that info for you.

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Old 05-12-2013, 07:59 PM
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Originally Posted by Pygmy
I'm running a HW Sct Pro Esc and 2s battery. I recently installed a Savox 1268 HV servo connected to my Esc (so not running high voltage) and noticed brown-outs, so I figured I'd hook up the servo directly to my lipo to
a) prevent brown-outs and
b) run it on 7.4v.
Tried that, seemed to work fine, now I was running my car again yesterday and I noticed after running for a while sometimes the steering wouldn't react properly again. The battery *was* running kind of low, but it still had enough oomph to power the motor...

To the best of my knowledge (which admittedly isn't very good) a 7000mAh 50C battery should be able to cough up 350 ampere, so to me it seems unlikely to be a brown out.. (?) The throttle was still working fine so the Esc hadn't even gone into LVC yet so I figure there should be enough power left to power the servo and RX as well.
So if it's not a brown out, what else could it be ?




Put a glitch buster capacitor on it before you try to hunt down the electrical gremlins. UFO is on the money though with his very detailed chart on how the system behaves under load! Also, what receiver are you using?
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Old 05-13-2013, 01:53 AM
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My setup :

Losi Ten SCTE
Hobbywing 3656SD 4-pole sensored motor (4700kv)
Hobbywing SCT Pro Esc
LRP C3 Rx receiver
Gens Ace 7000mAh 50c batteries

I already ordered the Novak glitch buster (#5626) for the receiver side, and the Timing Esc powercap (#5689) for the Esc side with the idea "Overkill! Better safe than sorry !" before realizing I really don't know whether the powercap would be of any use...

So with regards to the Esc-side power-cap :
- would it actually be of any use in my setup ?
- am I correct it should be soldered with red & black wires directly on the esc's battery connectors ?
- does it actually help if I install it this way on my Esc, or would the Novak power cap only work when replacing another cap (instead of just adding it like I'm planning to do) ?

Yes, I do realize normally the proper order would be to do my research first and the buying second, I was caught in the heat of the "must fix! must buy new stuff!" moment

Last edited by Pygmy; 05-13-2013 at 02:54 AM.
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Old 05-13-2013, 03:29 AM
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- It will help some
- Yes, to the ESC battery posts/connections.
- More capacitance is good, Speed Passion which at least used to be HobbyWing based sells upgraded larger caps, Novak too for some models. Should be OK.

Is it primarily a servo issue, or is the radio not responding, weird throttle too? If the throttle is having issues putting the glitch buster in the receiver as normal makes sense. But if the throttle is fine and it’s just steering weirdness it might be better I think to put the buster closer to the servo, of course that likely means splicing into the servo wire.

P.S. Am I right in assuming the receiver is also connected direct to lipo?

Last edited by Dave H; 05-13-2013 at 03:40 AM.
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Old 05-13-2013, 03:43 AM
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Sorry, no the receiver is powered by the ESC since it only goes up to 6v. I figured no longer powering the servo from the Esc would mean the receiver should be fine.
As far as I could tell it was just a steering issue, but I thought it would be impossible for the servo to brown-out when connected straight to the lipo...
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Old 05-13-2013, 07:35 AM
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IMO, putting a capacitor one the battery posts won't do much (unless it's pretty large). When the voltage drops, the capacitor is going to dump to help maintain voltage. The power that it contained is going to flow towards the path of least resistance, which in this case would be the battery. If you're trying to save the steering with a capacitor, I'd splice it like Dave H recommended into the servo wires. The thing that I would add to that is that you'd need to include a diode to keep the power from flowing back to the battery when the voltage sags. This way the servo is sure to get all it can from the cap.

The other option, since you're setup to run HV, would be just to run a separate battery such as the one of the one's in the following links. They weigh the same to just over what the cap(s) weigh, and you're guaranteed no issues.

http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html

http://www.hobbyking.com/hobbyking/s...ade_130X_.html
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Old 05-13-2013, 07:51 AM
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Originally Posted by ufoDziner
IMO, putting a capacitor one the battery posts won't do much (unless it's pretty large). When the voltage drops, the capacitor is going to dump to help maintain voltage. The power that it contained is going to flow towards the path of least resistance, which in this case would be the battery. If you're trying to save the steering with a capacitor, I'd splice it like Dave H recommended into the servo wires. The thing that I would add to that is that you'd need to include a diode to keep the power from flowing back to the battery when the voltage sags. This way the servo is sure to get all it can from the cap.
Since the servo is wired to the same battery connectors on the ESC, wouldn't that be the same thing ?
According to what I read on the novak website the power cap is supposed to be soldered to the battery connectors..?
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Old 05-13-2013, 09:10 AM
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What receiver are you using?
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Old 05-13-2013, 11:12 AM
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This is precisely why I avoid HV servos.
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Old 05-13-2013, 11:38 AM
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Originally Posted by rcgod
What receiver are you using?
See post #4
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Old 05-13-2013, 11:39 AM
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Originally Posted by Pygmy
Since the servo is wired to the same battery connectors on the ESC, wouldn't that be the same thing ?
According to what I read on the novak website the power cap is supposed to be soldered to the battery connectors..?
If I understand what you're saying correctly, no. They are different. The cap that you're referencing is to smooth out the power of the system, not help the servo. If you have the cap attached to the battery terminals, as well as the servo wires, the cap will feed the battery when it dips. You only want it to feed the servo. Therefore you'd need to diode between the battery terminal and the cap on the servo wire so that when the battery voltage dips the diode doesn't allow the power to flow back to the battery, only to the servo.
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Old 05-13-2013, 11:39 AM
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Originally Posted by rcgod
What receiver are you using?
I was curious also... He stated LRP C-3... I checked the specs... RX Says 4.6v-6.0v input voltage... Castle 10amp BEC would be a great $20 fix... But not with that RX...
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Old 05-13-2013, 01:31 PM
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Originally Posted by ufoDziner
If you have the cap attached to the battery terminals, as well as the servo wires, the cap will feed the battery when it dips. You only want it to feed the servo. Therefore you'd need to diode between the battery terminal and the cap on the servo wire
Since my electronics knowledge is fairly non-existent, can you draw me a simple schematic on how to connect the diode(s) ? (Should I use a Schottky diode ? I'm trying to read up on this as we speak)
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Old 05-13-2013, 01:59 PM
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Originally Posted by goatsblood666
I was curious also... He stated LRP C-3... I checked the specs... RX Says 4.6v-6.0v input voltage... Castle 10amp BEC would be a great $20 fix... But not with that RX...
My LRP C-3 RX is powered by the Esc's 6v BEC, which only has to power this RX since my servo is powered straight from the lipo. I figured that would take load off my ESC so the RX would be fine and the Servo would be fine..
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