HarryC

My Feedback: (1)

I have a JC 160sx kero start. Does anyone know what minimum voltage the JC ECU will allow before it either refuses to start, or may stop when actually running?

The reason I ask is that I am wondering about running it on LiIon rather than Lipo, and the nominal voltage and voltage under discharge of the LiIon is a little less than Lipo. I have run it successfully on LiIon but with recharging regularly, and I wonder how far down i can take the LiIon before the JC ECU complains. I have telemetry on the turbine battery so I can monitor it against any min voltage allowed by the ECU.

Dave Wilshere

Your using 2s A123?

The low voltage threshold which gives 50% turbine power (yellow/green flashing light) is between 6.0v and 6.6v. Unless the battery collapses in voltage its unlikely to stop, the max pump voltage will be around 4v.

I guess it depends if your batteries will deliver over 6v under the pump load (which is quite small)
My rule is if it has enough energy to start a kero turbine I fly (but on 2s Li-Po)

If you have your battery type set at 6N Ni cell type its nearest your battery type

HarryC

My Feedback: (1)

Thanks Dave. I am using Jeti Power Ions which actually start at the same 8.4V as a lipo but their nominal voltage is 7.2 rather than the 7.4 of a lipo, and their final voltage is 2.5V rather than the 3V of a lipo, so their discharge curve sits at a lower voltage than a lipo, at half discharge on a 5amp load I could expect around 6.5V. Telemetry shows the pump alone taking less than 1A at idle, haven't looked at it at full power, the ECU must take a little too but I expect that is very small.

Are you saying that at less than 6.6V the ECU will drop the engine to half power only?

Dave Wilshere

Harry

I think its below 6.6v The older ECU's were designed with Ni battery technology in mind and 1.1v per cell (6) was the weak battery warning and 1.0v per cell was the empty figure, so 6.0v

I don't remember exactly the figure it triggers the half power...will check, maybe the 6.0v figure

Len Todd

I have found that while the voltage appears to be staying up on the GSU readout, the battery may still not be able to deliver the current necessary to start, when ~50% of the battery's mah has been used. The voltage appears to stay up, but the turbine just will not complete the start cycle. Kind of like Dave said, if it starts, there is enough mah left to fly. Mine uses about 400-450 mah per flight, including a start. Other JC pilots in the club here that have tested various batteries have been seeing ~ the same consumption per flight.

mick15

Harry, why do you not use a jumper battery to start, as I.ve always done? Use a simple "y" lead with a fully charged 8v LiPo. You can then fly all day on the airborne battery which only has to power the pump.

m

Len Todd

Now there is an idea I had not thought of! Just have to be careful not to connect a fully charged LiPo to a significantly discharged one via the Y.

mick15

Len, it makes no difference whatsoever, besides you only have both connected for a second or two. Start on the larger battery connect the airborne, disconnect the start, fly.

m

Dave Wilshere

That's why we keep these.

Len Todd

Guess maybe you have never seen a LiPo go up in smoke and burst into flames. I have had two LiPos do that. One was a direct short and burned thru the plane out onto the floor and bubbled up the concrete. That one caused a total loss of the plane. The other was connecting two on a parallel charge cord before they went into the plane.One was fully discharged and the other was apparently fully charged. Fortunately it was out of the plane when I connected them to the Y. Lesson learned there was better charged battery management.

Of course, HarryC is not using LiPos, so in his case, it is irrelevant. But, if someone reads this and is using LiPos it is an opportunity to avoid the lessons I learned the hard way! Whether or not one chooses to learn from others mistakes is totally up to the individual.

Zeeb

My Feedback: (41)

My word, if you're worried about the LiPo battery safety and considering the possible risks/issues with "jump starting" your turbine, why don't you just get the A123 mod done on the ECU and run one of those batteries?

K.O.

My Feedback: (16)

+1

Len Todd

I am running V10 ECU. Don't need the mod.

You are right though, An A123 eliminates the problems for a fire. However, it is still not good to parallel up a fully discharged a123 to a fully charged one. The current inrush is still there. My point was if someone reader using LiPo does what was suggested, they could have a serious problem.

For me, I started out with LiPos. I am stuck with them for a while and there are specific reasons to use them.

I went with LiPo becasue A123s are not as light and compact. Two 2000 Mah LiPo Receiver Packs fit right up in the nose. Two are perfect for the powersafe capability and the CG comes out right on with two receiver packs up there. Also, two of these 2000 mah LiPo packs are only slightly heavier than one 2000 mah A123 and they LiPos are a lot thinner.

From an electrical perspective A123 would be better because they are designed to deliver higher currents for a longer period of time. That does seem to help on starts. But, using two a123s is just too big and heavy for my particular application.

Enough said. This thread is wandering off topic.

.

Zeeb

My Feedback: (41)

My response was for the OP who's running a P-160SX and it would have the Ver. 6 ECU which does require a modification to run A123 batteries.

Point being there isn't any perfect battery solution but I personally would not be relying on an Li-Ion battery for my ECU/starter operation. Their current output is way to restricted requiring a much larger mah rated battery to get the required discharge capability and they take overnight to charge.

HarryC

My Feedback: (1)

You must be thinking of old technology. The Li-Ions I use are rated at 40A continuous, 80A burst, near 2C fast charge, and weigh less than the equivalent Lipo.

Zeeb

My Feedback: (41)

Would you mind providing a link describing the above battery technology, I can find nothing that has the specs you list for Li-Ion?

HarryC

My Feedback: (1)

http://www.jetimodel.com/en/katalog/...r-Ion-RB-5200/

Len Todd

The 2000 mah LiIo in my Checkmate charges up in about 25 minutes. ?? It is also about 25-30% larger and ~25% heavier than my 2000 Mah LiPo Receiver Packs. ?? It uses about 100 mah per flight.