Why no auto LVC???

[littlejohn]

Have i missed something but there is no Auto LVC.. ie the ESC automatically detects the number of cells in the pack and set the LVC. Additionally, a custom LVC, where by you can set the LVC per cell. ie set to 3.2 and the ESC sets the LVC accordingly for the pack.
Why I ask? This would make changing between packs with different number of cells much easier.

Randy, if you read this. Can this be added to the next firmware ver for the RX8.. not so worried about the RS Pro, but would be nice nonetheless.

thx

[TekinTeamMgr]

I answered this on anothe fourm but I'll follow up it here as well.

We don't do auto cut off due to the possability that you can have packs overlap voltages. So we chose not do this for this very reason.

Chaging VC settins is a few button presses on the RX8 itself, no hotwire needed.

[ta_man]

Originally Posted by TekinTeamMgr

I answered this on anothe fourm but I'll follow up it here as well.

We don't do auto cut off due to the possability that you can have packs overlap voltages. So we chose not do this for this very reason.

Chaging VC settins is a few button presses on the RX8 itself, no hotwire needed.

Unfortunately, the cutoffs you can set with the buttons are not really safe for the batteries long term life. It is generally understood that for best life of a LiPo pack you should not draw it down below 20% remaining capacity. Voltage cutoffs in increments of 3V mean you end up drawing down to almost completely empty if you run to the cutoff.

How about this: A per cell cutoff voltage that could be set once with the hotwire (such as 3.5V/cell) and that is honored when you change the cell count with the buttons? That way, people who don't want to draw down their batteries all the way don't need the Hotwire every time they change cell count.

It seems that should satisfy your concern about overlapping voltages and still achieve the result requested for by the O.P. (and me too - I run 3.5V/cell)

[BrianG]

yeah, some type of adjustable value would be nice. Setting the # of cells you have, and the v/cell trip point would be nice to have.

ta_man: Wow, 3.5v/cell is actually quite high. The LVC would have to be designed to be less sensitive so that it doesn't get triggered simply by voltage drop under load during acceleration. 3.2v/cell seems to be the norm which allows max runtime without hurting the cell from deep discharge.

[ta_man]

Originally Posted by BrianG

yeah, some type of adjustable value would be nice. Setting the # of cells you have, and the v/cell trip point would be nice to have.

ta_man: Wow, 3.5v/cell is actually quite high. The LVC would have to be designed to be less sensitive so that it doesn't get triggered simply by voltage drop under load during acceleration. 3.2v/cell seems to be the norm which allows max runtime without hurting the cell from deep discharge.

Well, with my 4S cutoff set at 14V, I get at least 20 minutes from my MaxAmps 6000 packs and 15 minutes from my Fantom 4S 4300s. I've heard of people puffing the MaxAmps packs from running them too low and I want to avoid that. Actually, I've never even hit the cutoff - it is just there for safety. I usually want to to take a break and drive a different car after 20 minutes.

[BrianG]

I would be interested to see how much capacity (mAh) you put back into the cells once they do hit cutoff. Would give you an idea how much capacity you are losing by a high cutoff value. Better yet, if you have an Eagletree device, hook it up and see the performance over time.

I would also be interested to know how the Tekin LVC algorithm works. Does it average out quick dips in voltage (under startup or hard acceleration) to prevent false triggers, or are the cells actually staying above LVC all the time, even under heavy loads? I know from experience that the Novak external LVC (sorry to bring in a competing brand in the Tekin forum) is quite sensitive (time-wise) to any dip in voltage. As a matter of fact, I had to add a simple circuit to delay those dips somewhat to prevent false-trips.

[ta_man]

Originally Posted by BrianG

I would be interested to see how much capacity (mAh) you put back into the cells once they do hit cutoff. Would give you an idea how much capacity you are losing by a high cutoff value. Better yet, if you have an Eagletree device, hook it up and see the performance over time.

That is kind of hard to say because I have never hit the cutoff. And doubly hard because I almost never charge the pack up fully again afterward. Maybe one day I will just to find out. (I did that one time, a year ago to find out my amp draw with a different setup (MM/Neu 1512) but haven't tried it with the Tekin.) I've got an Eagletree. I might try it next time out.

The best estimate I can give you is that after 14 minutes of running my Hyperion charger estimated that I had 33% charge left in my Fantom 4300 4S pack. I don't remember if there was any marshalling needed in the 14 minutes but if so, it was not much.

That estimate could be off as much as 10% since it is based only on resting voltage and I didn't fill up the pack afterward to confirm the amount used.

[ticklechicken]

Originally Posted by TekinTeamMgr

I answered this on anothe fourm but I'll follow up it here as well.

We don't do auto cut off due to the possability that you can have packs overlap voltages. So we chose not do this for this very reason.

Chaging VC settins is a few button presses on the RX8 itself, no hotwire needed.

I had my MMM set to Auto-Lipo and I run 4s. I shut off my car to fix something and I must have been near 3.1 volts per cell (old firmware when only seeting was 3.0 v/cell). When I started the car, I only heard three chimes indicating the Auto-Lipo was set for 3s. With the new firmware, you can increase your v/cell, but there is still a risk in using Auto-Lipo. Those without the Castle Link cable are stuck with 3.0 v/cell. It's not likely to screw up when running 4s, but it did happen to me once. If I wasn't so OCD about counting the beeps, I would have had a problem. On 6s, you would only have to be at 3.5 v/cell to confuse the Auto-Lipo.

Personally, I think Auto-Lipo is not a good feature. Maybe it's okay for the Tekin, but it's not a good idea for the RTR's that come with the MMM. False sense of security for a likely unaware buyer.

[whitrzac]

Originally Posted by BrianG

I would be interested to see how much capacity (mAh) you put back into the cells once they do hit cutoff. Would give you an idea how much capacity you are losing by a high cutoff value. Better yet, if you have an Eagletree device, hook it up and see the performance over time.

I would also be interested to know how the Tekin LVC algorithm works. Does it average out quick dips in voltage (under startup or hard acceleration) to prevent false triggers, or are the cells actually staying above LVC all the time, even under heavy loads? I know from experience that the Novak external LVC (sorry to bring in a competing brand in the Tekin forum) is quite sensitive (time-wise) to any dip in voltage. As a matter of fact, I had to add a simple circuit to delay those dips somewhat to prevent false-trips.

well, from the 3 runs I made with my eagle tree before I keeled it... it def. doesn't cut out right away... I hit 7.3v under a 200amp spike....

and I did see someone puff a MA lipo by hiting the cutoff on the losi esc