low voltage cut-off

[urbs00007]

Purchased a couple Dimension Engineering CellShields. They are low voltage cut-off devices. It has a dial to set the cut-off voltage between 2.5 and 3.5 volts. I set it at 3.5. my fellow members of this forum recommend a 3.5 low voltage cut-off so that the resting voltage is around 3.7 volts. At 3.5 I cannot run the model as the low voltage cut-off kicks in almost immediately. So I called the manufacturer and asked them why it was kicking in so quick. They told me that they recommend a setting around 3.0 volts. I think I would destroy my batteries with that setting. why is there such a difference of opinion. I run revolectrix 420 silver graphenes 70c. 5,000 mah. 5s and 3s lipos. Any input is appreciated here. Thanks. By the way, these units are meant for electric aircraft. Is this why the recommended voltage cut-off is much lower ?

[Mxkid261]

FWIW I have a bunch of cheaper LV alarms and I usually set them around 3 or 3.2 otherwise they go off prematurely, doesn't matter if I'm running a newer high quality pack or a 5 year old beat up turnigy nano-tech. The pack's are never below 3.7 so I've never thought much about it, just figured they're over sensitive.

[urbs00007]

low voltage cut-off

FWIW I have a bunch of cheaper LV alarms and I usually set them around 3 or 3.2 otherwise they go off prematurely, doesn't matter if I'm running a newer high quality pack or a 5 year old beat up turnigy nano-tech. The pack's are never below 3.7 so I've never thought much about it, just figured they're over sensitive.

I am trying to come up with a low voltage cut-off that will allow me to run my setup for as long as possible without damaging my packs. timing my runs takes the fun out of it. is my goal impossible? how are the airplane guys running with 3 volt cut-offs?

[R2315]

I was interested in these cellsheilds as well but was worried about the 0-100% only throttle. I wasn't sure how slowing down in choppy water or the odd turn would effect it. Nevertheless timing is crucial and I'm not ready to trust these or the inaccurate LV alarms, I use those only to get a pass or two in after a timed run, I don't run my packs below 3.7 per cell... 30sec or so is not worth wreaking my packs or my boat. I found with the LV Alarm though it would set off during a run prematurely and if I stop the boat and wait a few seconds it would turn off and I would have at least one more pass above 3.7

[R2315]

Maybe the ones they produce for cars might better serve our application

[CraigP]

The batt voltage drops under a hard current pull, tripping off the LVC. There's not an easy solution... you have to set it lower so you can get the correct runtime, but it you just start cruising and quit running hard, then you can indeed over discharge and damage your batts. Remember, much past 3.6V and the voltage falls fast! You can pull up a LiPo discharge curve and see what I mean. So timing is really to only good tool that's cheap.

You can get a wifi data logger and get a readout of your used mah realtime on the shore... For me, that's a pricey route.

[R2315]

How about the Hitec HTS-SS Blue - Telemetry system, I believe you can program it to give you live alerts in real time on your phone for just about everything. Anyone using this?

[CraigP]

I watched a tutorial on this system. It's nice, but kinda pricey. But these real time systems are expensive.

[HTVboats]

looking at my data logger after testing with larger props for 2 lap and SAW runs, I see voltage drops to near 3.0v per cell easily. Still bringing in the boat and checking all cells they are well over 3.7 per cell. Under 3.75 per cell my setup is too aggressive be it SAW 2 or 6 lap heats. Check your cells after your run religiously and you will learn what you need about batteries and the load your trying to accomplish. Just like momentary high amperage spikes you get low voltage spikes under load. Some ESC's are more sensitive than others. Damage running cells continuously below 3.7 volts is different than a momentary spike below 3.0 volts. Bring them in above 3.7 per cell.
Mic

[kfxguy]

If your running the graphemes they don't damage that easily. Set it at 3.0 and when you get the first cutoff blip then bring it in. It shouldn't be below 3.5-3.7v resting at that point.

[CraigP]

Also to consider, most data loggers are placed at the end of all wiring and connectors, so it's also reading the drop of all that stuff. Some data loggers have an additional voltage input. You can place that directly across your batteries then see the difference in this reading to the data logger voltage. It will show you your drops. Make sure your wires and connectors are just warm to the touch after a hard run. If hot, then you should consider new connectors and perhaps larger wire. Hot wires and connectors are wasted power!

Note: my ET data logger came with 12 gauge wire. I found this not acceptable and replaced it with 10. I think 10 gauge should be the smallest wire used. My SW 180A ESC has 8 gauge wire on the input side. I run two 10's to that wire then land each 10 on the Cap Board, at different spots, to distribute the current over the Cap Board. Same for the negative lead. So I have a total of 4 #10 wires going to the Cap Board. BTW, two #10's equals a #8 wire.

[urbs00007]

alot of good information and I appreciate it. on my expensive builds I use graupner telemetry to monitor voltages. works well. my buddy's youngster is now driving my recoil 26 and doing great. before the recoil he was driving my daytona 37 with 3s2p in parallel for 10,000 mah. tried the remote lvc set at 3.5 and it worked great. when the lvc kicked in, the packs came back resting at 7.5 volts. got fired up and bought 2 more units to try on my twin cat. no good. too much draw and would hit the lvc almost right away. low draw setups work fine with the lvc units. not with higher draw setups. going to try setting lower shutoffs with the recoil. maybe I'll get lucky. if not, getting a decent stopwatch and will time the runs. I dont trust the youngster with my fairly expensive graupner radio. again, thanks everyone for your assistance. always learning !!!

[Peter A]

There is an inexpensive telemetry system. This one here at OSE

https://www.offshoreelectrics.com/pr...prod=ose-83279

I have run mine only a few times but it makes for an effective tuning tool. If you use power from your balance lead then it gives you the voltage in real time across two cells, and has an alarm which you can set. Added to that three temp sensors and gps that shows and records speed and gives a plot of your run.

Screenshot_2017-08-08-17-50-14.jpg

This was the first time I used it. The voltage only shows in real time, but it records the rest. I screen shot it from my phone. Did I mention it runs on android devices.

[Cobalt6700]

I run a CellShield on my mono and have found that it cuts off a little over the stated voltage too. I think I've got mine set at 3.4 and the packs usually show 3.6 straight after a run.

[urbs00007]

lvc

I run a CellShield on my mono and have found that it cuts off a little over the stated voltage too. I think I've got mine set at 3.4 and the packs usually show 3.6 straight after a run.

so your resting voltage after a run is 3.6? if so, has that damaged your packs. what is your setup?