Current Daw

[paul330]

The posts I have seen indicate that the max current draw for a NG screen will be 8A.  Whilst I understand that various other components will be powered through it, it still seems rather high.  I am planning my electrical system for an IFR system and am looking at an E-BUSS.  20A is the limit and 8 for the EFIS is simply too much.

So:

Can you explain where all the power is going and if it can be reduced?

Will there be a seperate power input to the autopilot that can be independantly switched off for power and safety reasons?

I believe you will be offering a battery backup.  What is the estimated life time and can you put 2 in series to increase the capacity?

Love what you are doing but the current draw seems to be a major issue.

 

[dynonsupport]

First off, the 8A draw is what you should fuse and wire for. It doesn't mean it draws that all the time, or even ever.

Just the screen draws about 30W, which is about 2.5A on a 12V plane. Well over half that power is just to drive the crazy bright screens.

Everything beyond this is due to external loads. The biggest is when the battery is charging. The battery will only charge when your alternator is on-line, but it can add another 2A when charging. We could reduce that, but then the battery would take many, many hours to charge.

You cannot double up batteries. The one we sell will run the unit and many external loads for at least an hour, and more if you don't have a lot hooked to the screen or you turn down the brightness.

So we're at 4.5A. The rest of that is made up of the power sources for the remote modules. That 3.5A of extra power is all theoretical and what the screen can supply, not what we plan to use in a normal system. We'd expect a system with a single AHRS, single EMS, and single GPS receiver to only be about another .5A. If you really want to, we'll support lots of AHRS units, multiple EMS units, and all sorts of other stuff, the screen can do that.

The servos are always powered separately, like they are today. You don't really need to turn them off. If the AP is not engaged they only draw a few mA. We do suggest you have a switch in case you need them off in a failure where they don't stop for some reason.

So, in reality, a system not charging a battery, but powering an AHRS, EMS, and GPS, and at full brightness will be about 3A. That's actually only about an amp more than a D180 today, and you get a much brighter screen, a map, and synthetic vision. Yea for incredible advances in watt per processor performance!

 

[paul330]

That sounds much more like it!

One more question. Can the power to the battery charger have a seperate breaker and wire? That way, the charger can come off the main buss and be disabled on essential power - or is there some other way to disable if necessary?

 

[dynonsupport]

As I mentioned, if your alternator is not on-line (voltage below 12.5 or so) the battery won't charge. So it sort of does what you want already.

But no, you cannot power the charging circuit differently, nor turn it off manually. I guess we could add the latter in software if it was really something people wanted, but it seems like a workload increase.

If you really want to do it now, the best thing is to actually put the whole NG system on a switch. If you have to go to essential buss, don't you want the NG system running on it's battery? Kill the power to it, and it won't draw anything off your buss.

 

[paul330]

Not really.  The idea of an essential buss is that you can run essential systems indefinitely off a standby 20A alternator.  The ideal would be to have the back up battery (which would presumably fully charge) and then if the main gen failed you run the EFIS on the essential buss with the battery as final backup.

As it is, there is not enough amps available to cover the extra potential draw of charging the battery.  The answer then becomes to dispense with the option but then you lose one level of redundancy.