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Old 12-16-2016, 04:45 PM   #1
Dude6935
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Default Series Hybrid Help Needed

So I have a project where I want to power a normal brushless heli motor with both AC power from a generator and batteries such that the system behaves as one uninterruptible power supply.

Essentially it is a series hybrid and I can't figure out an easy way to set it up.

Say I have an inverter generator which puts out 2000 watts max (1600w continuous). It also has a 12 volt DC output, but only at 8 amps.

I can run that AC power through a power supply (AKA rectifier?) to DC and run that to the ESC. But I am pretty sure I can't just splice in a battery pack between the ESC and the power supply, right?

I had considered running the 12v, 8 amp DC to a battery charger, then to the battery, but I don't know how to then run that battery to an ESC that is already connected to the generator's rectified power.

I have looked at generators, inverters, uninterruptible power supplys, etc. until I see them when I close my eyes, but I am quite stuck.
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Old 12-16-2016, 08:51 PM   #2
extrapilot
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There are a bunch of ways to do something like this. Simple would be a low-cost switching power supply- a PC or embedded systems type with whatever DC voltage/current you require as the out, and then parallel in a battery which has a power diode in between the pack and the switcher. With that, you have the switcher providing a DC supply to charge the pack, the pack to manage output when the switcher cannot (no AC input, or not enough supply power), etc. It isn’t quite this simple, because many switchers will shut down on overload- so you need to make sure the tolerance on shutdown is not exceeded by battery droop on peak demand.

You could use a power diode here, but you have about 0.7v loss in that link. At 50A, that is 35W, which is a lot of heat to dissipate. A better way is to use active switching (PFETs), where you can switch out the switcher as required, with very low loss.

I don’t think you will find this approach to be feasible for a helicopter. We don’t have the luxury of low power to mass ratio, and going from internal combustion to a generator to AC is inefficient. You would have to check on this- it depends on your generator and your IC plant, but gensets are not designed to be low mass- they are designed for reliable, continuous operation at high loads. You might do better with a BLDC as a 3-phase generator- then rectifying that and doing DC->DC conversion.
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Old 12-18-2016, 03:19 AM   #3
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You don't say the motor is actually powering a helicopter. Is it?
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Old 12-20-2016, 05:34 PM   #4
Dude6935
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Thank you, extrapilot for the suggestions. I like the idea of the switching power supply because I believe I understand the basic concept.

I tried to research the active switching (PFETs) but wasn't able to make any headway. Could you elaborate here?

I want to use all off-the-shelf components. So I am reluctant to try and build my own genset out of an ICE and a DC motor. I think small inverter-based gensets are going to be hard to beat.

npomeroy, it is an airship which uses RC heli components in the gondola.
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Old 12-20-2016, 09:19 PM   #5
extrapilot
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You could probably make do with a turnkey solar panel/battery switchover. Normally, they take the DC input from the panels, and route that to both the output and the battery (for charging). When the panel voltage drops below some set value, normally they then clip the linkage between the panel input and the battery, and route the battery to the output. I think this is more or less what you want, and you can get them for <$50 that can handle 30-50A at 24v DC. Note- some may not behave this way- and instead rely on the diodes in the panels to prevent reverse charging, but Im not aware of any quality switcher that does it that way.

If you needed, you could run a second component (a charger) from the genset to the battery, so that the battery is balance charged (assuming a lipo) by a specialized system. When the power fails to it- normally they have built-in protection to prevent reverse flow from the pack to the supply… So maybe a couple of components, but at least they are turnkey, and generally reliable and low mass.

Otherwise, you may need to learn a little about electrical engineering and microcontroller programming. Maybe a simple Arduino/Raspberry Pi could do the management for you, controlling the power switches (PFETs), and then you have a computer available to do other monitoring tasks, or to deal with navigation/telemetry/video etc. There are many people who could design/code this for you- myself included- but it will come at a cost that is probably many fold higher than using commercially-available switches like those used for solar or similar (wind, etc) installs.
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Old 01-09-2017, 01:57 AM   #6
Block137
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Replace battery with capacitors?
Or
Generator >> Switching >> Batt charger(preferably high power) >> Batt >> ESC
This way ESC is powered by charger and batt act act as buffer.
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Old 01-10-2017, 11:44 PM   #7
Anthony440
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Maybe just buy a vfd


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