Maximum voltage 9Xtreme board can handle

[vahegan]

We all know that the 9Xtreme board can handle much wider input voltage compared with stock 9X board and that it uses much more efficient switching regulators. My question is, what is the maximum voltage that can be applied to the board? This is probably limited by the regulator chip used and the capacitors at the input. Is it like 35V max?

I am asking this because I came across some inexpensive 14500 LiFePO4 batteries which are the same size as conventional AA batteries. LiFe-s are 3.2V, however, and get to 3.8V when fully charged. That is, if I put 8 such batteries in 8S1P setup into the original battery holder of the 9X, I will end up at 30-31V fully charged. Will the board be able to handle this voltage efficiently?

Or, is it better to try to modify the battery holder for a 4S2P setup? This will result in 15-15.5V when fully charged and I assume it should be in the acceptable range. Another advantage is that this latter setup will not require a 8S charger.

[MikeB]

It's not so much the 9Xtreme, but the Tx module as the battery voltage is also supplied to this.
The FrSky XJT is reated up to 15V, while the DHT (and DJT I assume as it is the same thing in a case) is rated to 13V.

I would therefore suggest limiting the battery voltage to 12V, or THREE of the cells you are suggesting.

I would also suggest NOT using the battery holder supplied with the 9X. These are likely to provide poor connections to the cells.

DO, however, use the wires and plug from the battery holder to connect to whatever battery you use, and be SURE not to reverse the battery connection.

Mike.

[s_mack]

It never occurred to me anyone would want to use high voltages like that

The voltage range of the 9Xtreme is suitable for any 2S or 3S Lipo application... that was the target. It was NOT designed to handle anything greater than fully charged 3S (12.6V). On the low end, it should be OK down to a somewhat depleted 2S (let's say around 6.4V). The other "common" setup is going to be the 8xAA drycell options, which is of course 12V and within that range as well.

When designing for power, the goal was to improve upon the 9X but not necessarily to the extent that any battery configuration possible would work. Getting components that work at 15V and above is much more complicated and expensive, and frankly there's no benefit to it for this application. Like I said, it never even occured to me that anyone would try!

The stock 9X couldn't handle voltages under around 7V, which meant a 2S was impractical because you needed to keep it fully charged. A 3S, however was wasteful because everything above 7V was burned off as heat due to the inefficient linear regulator. The 9Xtreme improves both situations. A 2S is happy all the way down to its normal discharge levels and a 3S is efficiently used with the switching regulator.

[vahegan]

It's not so much the 9Xtreme, but the Tx module as the battery voltage is also supplied to this.

So the radio module is supplied directly from the battery? I thought the battery is only connected to the 9Xtreme which was handling the power supplied to all other components inside the case.

The FrSky XJT is rated up to 15V, while the DHT (and DJT I assume as it is the same thing in a case) is rated to 13V.

OK. I'll be using XJT, so I assume, theoretically, I could have up to 4S of LiFe, which is 15.2V fully charged.

I would therefore suggest limiting the battery voltage to 12V, or THREE of the cells you are suggesting.

OK, then I'd be probably better off using 1500mAh LiFePO4 3S batteries from HK

I would also suggest NOT using the battery holder supplied with the 9X. These are likely to provide poor connections to the cells.

DO, however, use the wires and plug from the battery holder to connect to whatever battery you use, and be SURE not to reverse the battery connection.

OK, got it. I am sure I won't mix the polarity, at least if the board is correctly marked

It never occurred to me anyone would want to use high voltages like that

Oh, I am a strange person known to often attempt things no one else would think of doing

The voltage range of the 9Xtreme is suitable for any 2S or 3S Lipo application... that was the target. It was NOT designed to handle anything greater than fully charged 3S (12.6V). On the low end, it should be OK down to a somewhat depleted 2S (let's say around 6.4V).

When designing for power, the goal was to improve upon the 9X but not necessarily to the extent that any battery configuration possible would work. Getting components that work at 15V and above is much more complicated and expensive, and frankly there's no benefit to it for this application

OK, thus the operating range is from 6.4V to 15V. I think it's worth mentioning this in the specs section so that anyone interested to know would easily find out.

Like I said, it never even occured to me that anyone would try!

Well, I thought that since the stock battery holder was designed for 8AA cells and since there are 3.2V LiFe cells that would fit nicely in this, than why not give it a go if the voltage would still be in the acceptable range. When I design small circuits I usually connect the power through a LM2596 based board which are available in China for $1/pc. or even less. They are rated at up to 35V input voltage. The efficiency is around 80% due to the use of a Darlington transistor as the switching element but this is sufficient for most non battery operated circuits. I was assuming that you used a similar circuit but with a more effective FET-based switch or maybe even synchronous rectification if you are talking about 96% efficiency but I didn't expect the voltage limit to be as low as 15V

The apparent disadvantage of my idea with 8 LiFe cells was in having to use a 8S charger and in having to make a 8S balance connector for the battery. It turns out that there are many other disadvantages, so I'd rather not go this way.

Thank you, guys, for all the comments and explanations.

[MikeB]

Yes, the battery does only go to the 9Xtreme, but the soft power switches for the modules switch the battery voltage, not some lower regulated voltage.

I normally use LSD (Low Self Discharge) Nimh cells, you can use 6 to 8 cells. This has the advantage of being able to be charged using the charge socket in the side of the Tx.

Mike.

[vahegan]

I normally use LSD (Low Self Discharge) Nimh cells, you can use 6 to 8 cells. This has the advantage of being able to be charged using the charge socket in the side of the Tx.

Mike.

Yeah, that's an option. I thought about using eneloops, but by using the internal charger the battery cannot be balanced, as they did not provide for the connectors between the cells. Well, with a little work, a balancing connector can surely be added for using with an external balancer...

[jhsa]

You do not need to balance charge eneloops..

João

[vahegan]

You do not need to balance charge eneloops.

Why not?

[s_mack]

OK, thus the operating range is from 6.4V to 15V. I think it's worth mentioning this in the specs section so that anyone interested to know would easily find out.

Nope, not 15V... I make no assurances whatsoever that 15V would not fry it. I designed it with 12.6V being the upper limit. It might survive 15V, but if so then its a happy coincidence and not by design.

2S, 3S, or 8xAA. Stick to that

4xAA might work. I think it'll work down to 6V. But again, I wasn't expecting anyone to try so I don't really know.

[MikeB]

All NiMh cells may be charged at c/10 continuously with no damage or problems. After charging with a peak detect charger, you may simply charge them at C/10, or less, for a while. This will ensure any cell that is at a lower state of charge than the others becomes fully charged.

Mike.

[jhsa]

You do not need to balance charge eneloops.

Why not?

well, I'm not an expert in batteries but I guess the NiMhs are more voltage tolerant than Lithium based batteries and also will balance automatically.
Lithium batteries can not be charged or discharged at any time over a certain voltage or the cells will get damaged, that is why balancing is very important...
Never heard of balancing NiMhs anyway..
Again, I'm not an expert in batteries..

João

[vahegan]

Nope, not 15V... I make no assurances whatsoever that 15V would not fry it. I designed it with 12.6V being the upper limit. It might survive 15V, but if so then its a happy coincidence and not by design.

Hmm. Sounds very strange to me. What components do you use that 12.6V is OK but 15V is too high? Sounds very strange to me. And it is always suggested for any design to have at least 20% safety margin to maximum recommended ratings for any electronic components. Or, do you mean that the efficiency of the switching regulator will drop beyond the specified value? But normally that must be well beyond frying any components.

All NiMh cells may be charged at c/10 continuously with no damage or problems.

Oh, I didn't know, this explains it perfectly. Thank you, Mike. It seems to me now that Eneloops or alike may indeed be the most convenient solution so far.

[Kilrah]

NiMH "balance" themselves on their own as long as you're charging them slowly (C/10-C/20). Cells that are full simply dissipate the excess as heat while the other finish charging. Obviously the current must be low enough for that amount of heat to stay reasonable.

[s_mack]

Hmm. Sounds very strange to me. What components do you use that 12.6V is OK but 15V is too high? Sounds very strange to me.

Why does that sound "strange"? 12.6V is 12.6V, 15V is higher than that. 15V is actually quite high for consumer electronics, with the vast majority of modern devices operating at 5V. There are literally millions of components out there, and they all have different voltage capabilities. Here,I randomly selected a component on DigiKey... happened to be a common capacitor. It is rated to 10V. So I didn't use that one, because I wanted to design for 12.6V. Strange?

And it is always suggested for any design to have at least 20% safety margin to maximum recommended ratings for any electronic components.

Where is that rule? 20%, 10%, 40%... the fact is, if a component is rated for 12.6V then it is declared to work reliably at that voltage or lower. It will *probably* survive @ 15V, but it isn't rated for it. As I said, the design specification was for 12.6V, not 15V. I'm not saying it will blow up @ 15V, but that was not the design intent so it *might* blow up @ 15V! What's it matter... you know the specifications, so simply choose not to exceed it. Can you suggest any reason at all for using 15V? There's no point in using 12.6V other than it is a common battery. The device requires 6V so there's really no reason to use anything higher.

There, forget 20%... I gave you 200%!

[jhsa]

I believe the RF module could be more of a problem than the radio itself. Depending on which module is used of course. I don't know any RF module that is rated for higher voltages either.

João