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Author Topic: 24VDC to 120VDC  (Read 4687 times)
Justme
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« Reply #15 on: December 28, 2016, 04:16:55 PM »

I was thinking in terms of the His Lardiness Lord Frotter's experience with overdriven alternators when it comes to longevity.

Damm you.

I now want to go read that thread in its entirety again.

Been there done that twice now already.
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Scruff
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« Reply #16 on: December 28, 2016, 04:57:24 PM »

iirc His Lardiness' problems had more to do with belt alignment and pulley ratio than overloading.

The link you posted N2 is the same as the link I posted.  whistlie

Of course the difference between an aviaton alternator and an automotive alternator is the carbon content in the brushes, the rotation direction, the ventilation and 600.
I'm entirely happy to load the replacement alternator to design spec. combined with a 1kWh battery linked to a 300Wh battery.

The battery does what it's asked in my book, it's electron flow, I'm fitting an auxiliary traction battery not a cranking system as you are describing. 125% overload is assuming the load is running at full load, the system is 100% efficient and the pulley speed is at rated RPM.
I am designing to max. load, spec-ing to 50% duty expecting 20% duty...I assure you if I catered for 100% duty I'd have an awful lot of highly sophisticated deadweight.
« Last Edit: December 28, 2016, 06:30:06 PM by Scruff » Logged
marcus
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« Reply #17 on: December 28, 2016, 08:26:56 PM »

cessna 172 / piper cub 'old and primitive'? certainly. 'durable, reliable'; mmm... well, TBH that wasn't my experience  Grin . 'serviceable'? well they have to be that!

the good thing about the alt being on an aircraft engine is lots of cooling air, assuming you're not running it flat out on the ground. I'd be more worried about the drive to the alt - it's a long time (20yrs) since I looked under the bonnet of a piper but I seem to remember a regular car type single vee belt drive for the alt, and in my experience these can start to slip long before you get to 2kw alternator load. I guess if they fit 100a 24v alts nowadays they must use a suitable drive system? but i'll let you worry about that.

looks like a regular UL listed 120v inverter and, if possible, 120ac 'load' to save on 12v psu's is the way to go. Good luck!
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Scruff
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« Reply #18 on: December 28, 2016, 10:00:10 PM »

By old and primitive I was talking specifically about the engine mechanics and electrics, just the way I like 'em. I'm so used to looking at multiplexed garbage and problems with warning systems rather than the system it's monitoring eg. abs sensors. I find most modern auto-electrics more hassle than their worth after > 7 years of entropy. Features like limp home mode because the add blue ran out... fume
Can't even wire a tow bar without a black lekytronic box these days.  facepalm
Any machine running after 40 odd years has my respect.

Yurp single V-belts are muck and the Cessna is sporting one, probably want a 7 pk or better for intended porpoise. Haven't heard back from the rest of the "development team" after I sent them a ballpark cost and logistics appraisal. ...

...all academic atm methinks.
The load is DC, the reserve battery can be 120V, so if I go with the inverter it'll be alternator -> inverter -> battery charger/ full bridge rectifier -> battery -> load ...triple conversion  facepalm....anyone sees a DC boost reg. for big toys let me know...
« Last Edit: December 28, 2016, 10:09:09 PM by Scruff » Logged
jonesy
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« Reply #19 on: December 31, 2016, 03:52:45 PM »

I'd be tempted to go 24V to 230V ac, as you might struggle to get a 120VDC lipo charger for 120VAC.  I have stacked to get a high voltage charger in the past, so 2 x 48VDC (lab) supplies, then a charger for the last bit.  You need floating supplies with good low impedance.  I used LF types. HF ones might be unstable if you used a PWM charger.
In terms of 120V to 12V, pretty much any domestic/commercial wall wart/psu will work from around 90VDC to 380VDC. When I ran a 96V battery for my inverter I didnt find anything that didnt work.  Most commercial psu spec sheets will show a DC operating voltage.
Do be careful with any isolation switch at 120VDC.  There are plenty that will break off load, but ones that will break the kind of power you're talking about on load (emergency shutdown) are big and expensive.  I worked on a project with 200VDC motors and we found that the cheapest way to get on load isolation was series wired 3 phase switches; some are spec'd for DC on the data sheets.
I keep thinking that 48VDC would be quite easy to obtain (floating 24V DC/DC remote sense charger in series with main 24V), have a 40V battery after losses, then smaller DC/DC to 12V. Lots of telecom stuff for 48V, but probably easier to use triple converters.
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Scruff
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« Reply #20 on: January 01, 2017, 11:14:23 AM »

I was thinking of just using a rectifier on the inverter output and using constant voltage to charge the batt. 30 series cells = charge termination 4.0V p/c @ 120VDC.

Inverter output can be whatever's easy to work with though. I just hate imbedding losses in systems...triple converters... Roll Eyes alternator 50% efficient, inverter 85% efficient, battery charger 80% efficient or rectifier quiescent loss at full load 20W.

I decided against converting back down, another reason I like 120V I can use 'murican kit. Too much weight and liability otherwise. I insisted the load voltage be the transmission voltage. Radio silence since I sent a cost estimate in and put the foot down on 12v shenanigans.
« Last Edit: January 01, 2017, 12:06:33 PM by Scruff » Logged
jonesy
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« Reply #21 on: January 01, 2017, 12:14:36 PM »

I've never played with Lipo. The lion cells I've got will take as much current as you have.  I put a 1.3Ah cell across a dc supply and it took a massive current; it was worse with a taper charger as the open circuit voltage being >4V just seemed to encourage it to pull more juice and they never reached end of charge. 
What altitude are you working at? Pretty much anything is good for 2000m, but the dielectric properties start to change and it's worse with higher voltages ie dc/dc converters.
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Scruff
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« Reply #22 on: January 01, 2017, 01:20:36 PM »

I've never played with Lipo. The lion cells I've got will take as much current as you have.  I put a 1.3Ah cell across a dc supply and it took a massive current; it was worse with a taper charger as the open circuit voltage being >4V just seemed to encourage it to pull more juice and they never reached end of charge. 
[/quote]

Glossing over the fact that I ought to have temp. monitoring, cell balancing and active current limiting.  whistlie That's probably not going to happen for a prototype. The advantage of LiPO over LA other than the energy density is absorption = float. Once they hit 4.0V p/c theoretically the batt voltage ought to oppose the rectifier voltage and stop charging without intervention.

End of charge for li-ion is spontaneous combustion.


What altitude are you working at? Pretty much anything is good for 2000m, but the dielectric properties start to change and it's worse with higher voltages ie dc/dc converters.

150m to 300m
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Nickel2
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« Reply #23 on: January 11, 2017, 08:19:06 PM »

Are you allowed this sort of thing in a plane, or does it have to be FAA/CAA approved?

http://www.sp-shop.co.uk/Sterling-Power-Hi-Perfomance-24v-140A-Alternator-PN-AL24140.html
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EpEver 4210A at 24v
24V 400 Ah battery. (4x200Ah FLA)
EpEver STI1000-24-230 pure sine inverter
Of course it'll work. (It hasn't caught fire yet).
Scruff
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« Reply #24 on: January 12, 2017, 09:22:54 PM »

What's this in aid of N2? I want a power supply not a battery charger persay. I can use a properer charger on the deck.
You'll get full field from an alternator just by loading the battery enough.
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Nickel2
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« Reply #25 on: January 13, 2017, 08:27:52 AM »

Anyone got any ideas how to charge a 120V battery with a 24V alternator?
~ 2kW > 2.5kW would be ideal.

I'll settle for constant voltage if a charger is too much to ask for.


 Sad Only trying to help!   Cry    I seem to have misunderstood the original topic   surrender
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1.140kW mono south-facing at 49*
EpEver 4210A at 24v
24V 400 Ah battery. (4x200Ah FLA)
EpEver STI1000-24-230 pure sine inverter
Of course it'll work. (It hasn't caught fire yet).
Scruff
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« Reply #26 on: January 13, 2017, 12:52:32 PM »

No worries N2, I appreciate the input.
Methinks this project is a white whale.
I said I'd sort the power after they sorted the load and I've yet to hear back.

Sterling are kindov spoofers I find. Their products do work but the components they use are cheap and unreliable. The claims they make about advanced fast charging is 60% upgraded cable. I'm not denying they work but fixing alternator charge issues is like shooting fish in a barrel, they're always so bloomin' dreadful to begin with.

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