4S goes into half speed in 3 laps, while 3S runs for over 40 laps?

[1945dave]

It has taken several weeks now to lock in on a fact that I am having some kind of problem with my newest 4S (2 x 2S in series) battery setup. A Hobby King Surge Crusher with stock Turnigy 3674 2,045 KV motor, Octura X440 prop.Turnigy 120 amp ESC. The situation started from the first time I tried the new 4S setup with 4,000 ma batteries and 35 – 70 C discharge rating that I get almost no run time before the esc drops down to half throttle. The boat leaps onto plane and flies for about three laps then slows to that half speed safe speed. Opening everything up the batteries, esc and motor are pretty cool to the touch and then I put in my 3S setup (3300 ma and 20 – 30C) and it runs great for the duration of a normal 4 minute run. When I come home to top off the batteries the 4S batteries (2S one at a time balance charging) charge for 38 minutes and the capacity indicated on the charger to reach full charge is 1500 ma. Both batteries do this almost exactly the same. The 3S single battery charges 53 minutes and the input capacity indicates 2870 ma.

This is puzzling. I have considered several things. Is the ESC going into a protection mode for some reason? Are the batteries not delivering full voltage because of my series wiring harness? I only have the one 4S setup so nothing to compare it to easily. If I could make a run with a single 4S battery and eliminate my series harness that might tell me something. Otherwise I am at a loss trying to figure this out. I went back and completely reconfigured my B6C charger making sure the cutoff time was long enough (120 minutes), that the battery capacity was listed correctly as 4,000 ma, and of course that the voltage was correct 7.4 volts (2S) and the delta peak voltage was set to default for lipos as 4.20 volts per cell. This is a challenge. I really like the way 4S makes this Surge Crusher pop. A very noticeable performance increase over 3S. But the longest high speed run I can make is maybe 4 laps on 4S while I can make 30 laps on 3S with no problem before the half speed mode kicks in. any thoughts?

[martin]

This can be a common problem on Seaking & Turnigy 120a & 180a esc with the lvc cutting in to soon. A lot that have this problem use no lvc at all & time runs. What voltage do you have the lvc set at & are you using auto on the cells or setting manualy.

[roadrashracing]

3s 11.1 v x 2,045 kv = 22700 rpm
4s 14.8 x 2045 kv= 30266 2pm

as you can see the 4s is using lots more power so draw will be a lot more. If you are looking for more run time with your 4s setup get a lower kv motor.
I was told around 30,000 for racing or 25,000 for sport boating.

[1945dave]

Hello roadrash. Your math is right where i want it to be. I am not one of those guys that wants 10 minutes running time. I just find 3 laps really short before the low voltage cutoff circuit kicks in. The battery is not nearly discharged at that point.

Dave

[JIM MARCUM]

Hello roadrash. Your math is right where i want it to be. I am not one of those guys that wants 10 minutes running time. I just find 3 laps really short before the low voltage cutoff circuit kicks in. The battery is not nearly discharged at that point.

Dave

1945Dave, 1945Jim here. Martin is right, check the low voltage cutoff setting - it's likely set too high. If I recall correctly it should be set at 3.7 volts/cell due to voltage drop under load kicking in the ESCs low voltage cutoff. JIM

[Alexgar]

The infamous turnigy lvc problem

[JIM MARCUM]

1945Dave, 1945Jim here. Martin is right, check the low voltage cutoff setting - it's likely set too high. If I recall correctly it should be set at 3.7 volts/cell due to voltage drop under load kicking in the ESCs low voltage cutoff. JIM

PS: Dave, I recommend buying a T180 ESC as it is more adaptable & more bulletproof than the T120. Just my opinion. JIM

[1945dave]

Thanks for everyone's input. But, why does the lvc not kick in too early on the 3S batteries only on the 4S? How can I test the actual voltage that this occurs?

Dave

[1945dave]

Yep, I have the T180 on order but it is on back order so I have no idea when I can expect it.

Still would like to double check the actual voltage that this lvc circuit cuts in. I am not sure if cut off should be nominal 3.7 volts though. I am thinking it should be more like 3.2 volts under load. My B6C charger discharges lipo cells at 1 amp load until the cutoff voltage is 3.0 volts per cell. That might be too much but 3.2 volts per cell would not scare me.

Thanks, Jim

[Alexgar]

I have three t180s and the lvc only works o one its probably a qc issue

[1945dave]

Thanks Alexgar.Still would like someone to tell me how I can test the actual lvc number for my particular ESC and also also why it would function reasonablly for a 3S configuration and not the 4S?

Dave

[masonis1]

Now I debt know the answer and I have to saw my big ezrun 150a esc in my 1/8 trug does this and if I.come to a complete stop and then.it will go.full.power then.lvc then the.same. I don't know why it does it but I'm like the guy.above. Just answer why.and help instead of telling "the.notorious turnigy" I want help and sounds like the guy above does too.

Sent from my SPH-D700 using Tapatalk 2

[JIM MARCUM]

Dave, PM drwayne. He may have the info you need. JIM

[masonis1]

Then can you please post the answer here

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[jcald2000]

Turn OFF the voltage cutoff and time your runs. The low voltage cutoff is Not reliable!!!!