48VDC generator head

Re: 48VDC generator head

stephendv wrote: »

Using a midnite classic as a transformer seems an expensive option. In all cases it would be really neat if you could link the output voltage to the RPMs, so could effectively build a fuel efficient battery charger that slows down for absorb.

I already got four Classic 150's. The reason I'd be running the little generator is probably to maintain the bank during continuous heavy draw times like winter evenings when it's really cold and the wind isn't blowing. So all I have to do is put another breaker in the solar combiner to hook the little generator up to, go to the Mode menu on the Classic and select a different input source, start the little generator and voila! Diesel Powered Solar Panels! 8)

papa wrote: »

Hatz rates that engine at 3.5kW @ 3600 (I assume at sea level), so how did you arrive 4.2kW? Just curious.

I thought I had posted this but I don't know where the post went. Anyway - I assumed it was 6 hp. The engine was given to me because it wouldn't start. There's a snap ring on the injection pump that came off so the pump plunger wasn't following the cam. I put the ring back on and it runs fine. So I never actually looked to see how much power it has, and it don't say on it. I see it has 4.8 hp. No matter - I can match whatever with the Classic on it. If I need more power maybe I can put a little turbocharger on it and bump the fuel rate up a bit
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Chris

Re: 48VDC generator head

BB. wrote: »

Variable RPM Diesel DC Generator with an MPPT controller (Midnite Classic)--Now that could be a marriage made in heaven for optimum use of fuel. Use some sort of biodiesel fuel (i.e., oils from seeds), and it actually could be very sustainable.

Bill, when I emailed Ryan and boB about this and asked them if they thought it would work (they said it should), I had the theory that I can control the throttle on the little Hatz with a stepper motor using the AUX 2 PWM drive on the Classic with Waste Not.

The Waste Not mode pulses that PWM more and more as the batteries charge up. I've been using it for quite some time to operate my water heating system. I'm pretty sure the PWM output of the Classic can be used to drive a stepper motor to make the engine progressively idle down as the bank gets charged up. I haven't tested that yet, but the pulse width and voltage is about the same as used on most automotive applications for things like fuel injector drive and throttle control for cruise controls.
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Chris

Re: 48VDC generator head

The Classic's PWM does not control the load. It's merely an output based on battery voltage. The PWM CAN be used to control a load like I do with my water heating system where it drives a AC SSR that turns the 2,000 watt AC heater elements on. But I can also be used to control anything that works with PWM.

In the case of the generator when the voltage gets to the charge stage set point, minus the offset in the AUX 2 setup menu, the PWM starts pulsing. The more power that is applied to the situation, the higher the voltage will try to go, and the more the PWM pulses. So if the generator is charging and the voltage reaches Absorb set point, the PWM is going to start pulsing. The PWM signal can be used to operate a stepper motor to slow the engine down and reduce output. Now, output is reduced so the system voltage drops, the PWM reduces the pulse voltage and makes the engine speed back up, putting out more power.

PWM is very smooth at the high frequency it operates at in the Classic, so it will find a "balance" of how much generator output is required to maintain charging voltage. This I know beyond the shadow of a doubt will work.

The only thing I haven't tested is if the stepper motor I got, which is off a Cummins genset with an electronic throttle, will work with the Classic's PWM drive. The stepper motor says 0-5.5 VDC - 0 volts the plunger is fully extended, 5.5 volts the plunger on it is fully retracted.
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Chris

Re: 48VDC generator head

It could be. Cummins calls it a stepper motor and it runs the throttle lever on an old NT-series genset with electronic frequency control. Like I said, I haven't tested it yet to see what it does with the Classic.

This is for Rob - (Fordguy64) - is your Lister a 900 rpm engine? If it is this generator off my 12G turbines will work on it:

https://picasaweb.google.com/110979388690716770927/12GTurbineBuild#5757339619529501442

It's got pinned mags and I run that same generator at 1,200 rpm on the 350 MPPT turbines. It has 8.54 rpm/DC volt so at 900 rpm it makes 105 open DC volts. The gen rotors are 254mm. The winding resistance in wye is .47 ohm and the windings will handle 36 amps continuous. Your loaded voltage is always less than open. But if you "clamped" the voltage down to like 90 with the Classic, that would give you 32 amps @ 90 volts, or ~ 2.9 kW input to the Classic. I'd have to look up the efficiency curve to see what it is at 32 amps continuous output, but I think it's over 90%, or very close to it, so it will run fairly nice and cool at that power level.

If you don't have facilities to machine rotors, I got a set here with 1" bores (fit on a 1" OD PTO shaft), with the pin holes for the mags already drilled. I quit building generators with neo mags when the price went thru the roof, and designed new ferrite magnet generators instead. So these are a little rusty from laying around in my shop for the last two years, and I never sprayed them after I machined 'em:

Attachment not found.

The stator has 50 turns, 9 coils, 13 AWG windings and I can give you all the pin dimensions for the coil winder if you want to build one for your Lister. If your Lister is a 1,800 rpm engine, just wire the stator delta (or reduce the number of turns in the coils to 25) and it would still work. I have spun these small diameter generators up to 2,000 rpm and they hold up fine. But the bigger ones with 355mm rotors fly apart over 1,500 rpm. And the explosion is really impressive. It puts holes in the shop ceiling and blows the generator right off the test stand.
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Chris

Re: 48VDC generator head

Yes, permanent magnet generators are usually more efficient than wound field because the field strength is incredibly powerful compared to wound field. This allows windings with fewer turns of bigger wire which reduces internal resistance of the winding. They are also typically wild AC and run at very high frequencies - usually in the hundreds of hertz on a wind turbine.

The downside to permanent magnet generators is that they are extremely dangerous to work with during assembly, dis-assembly and handling rotors. The attraction force between the two rotors in the above generator that I referenced for a wind turbine is around 1,700 lbs. If anything slips while jacking a rotor down, and you happen to get your fingers in between you will not have any fingers left. When an uncaged rotor is removed from the generator it must be handled with care and packed away where metal objects can't be attracted to it. An uncaged rotor will turn metal objects in the shop into dangerous missiles from incredible distances, and if you happen to be in between a rotor and something it suddenly decides it wants, you're not going to be all that impressed with the situation.

Four years ago me and two other guys were replacing the stator in a Proven 7.5 kW turbine, jacking one rotor down. The jacking screw slipped out of the socket and one of the guys got his whole hand in between the rotor and the stator. It took us about 15 minutes to get the rotor jacked back off the stator to get him out. His hand was not saveable - they amputated it about 4" above his wrist.
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Chris

Re: 48VDC generator head

swmspam wrote: »

I'm not entirely convinced of this. MPPTs use a closed-loop feedback mechanism to "search" for the global peak power on a Voltage-Current curve.

I use Classics on all my wind turbines. You use the Wind Track mode in the Classic and program a curve for it. A piston engine generator is no different than a wind turbine - just uses a different engine.

The main advantage is not having to use huge cables from a high amperage DC genset to the battery. With the Classic I can transmit power at 120 VDC from the genset to the controller at low amps, and the high amp wiring is short from the Classic to the battery.
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Chris

Re: 48VDC generator head

swmspam wrote: »

So, to answer the fundamental question if a MPPT can optimize a piston engine, I think the data suggests "no".

The idea is not to optimize a piston engine. I can program a wind curve in the Classic to match electrical loading to available shaft power at any rpm I want to run the engine at. The idea is to optimize electrical efficiency. DC generators have absolutely horrible electrical efficiency on battery charging duty at high outputs - take a look at the Alten 2480 or 4850 as an example.

Our battery bank is in a utility room on the side of the house so if I want to charge the bank at full output how long do you think my wife is going to put up with a noisy Hatz diesel running only 10 feet away from the battery bank?

It's going at least 75 feet away from the house, on the other side of the shop, so we can't hear it running in the house. The total wire run length to get the power to the bank is about 85 feet by the time you make all the corners. By running that generator at 120 volts instead of 60 I cut the amps in half for the same power output, improving power efficiency in the generator head itself, the rectifier, and power transmission from the genset to the utility room.

If people want to put their DC genset right by the bank and listen to it run that's fine by me. If people want to lay 2/0 cable to get the amps from the generator to the bank from further away, that's fine by me too. But I'm not doing either. I already got a Classic, I got a place to hook the generator up by the solar array far away from the house where we won't be able to hear it running, so I'm going to use the high voltage/low amperage method "just because I can".

There's one other advantage to using the Classic on a DC genset - it provides a state-of-art charge controller that will do proper bulk/absorb and even EQ if you want - with temperature compensated charging stages.
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Chris

Re: 48VDC generator head

swmspam - interesting topic for sure - and it's not silly.

I have to point out, however, that with wind turbines and piston engine generators we do not use MPPT. It is a programmed power curve - a dyno curve that fits the unit being controlled. There are various curves for different wind turbine models on my website:
http://dairylandwindpower.us/Classic150_PowerCurves.html

The controller loads the wind turbine (or piston engine generator) identically to the way a dynamometer would load it. With a piston engine there are only two parameters that are adjustable for a given load - speed and fuel rate. Shaft power is a function of speed and torque (hp = torque x rpm / 5252). So if speed is reduced, torque has to increase to power the load. In order for torque to increase at the lower speed, the fuel rate has to be increased. This is where the brake fuel curve is established - in torque rise as speed is lost due to loading by the dyno.

So you have to forget the MPPT concept. Go to the dyno room instead. That's what we're doing here. That Classic, in conjunction with the electrical components the engine is powering (generator as the dyno, Classic as the controller, battery as the load bank) is the same thing as an eddy current dyno. And we get a torque reading from the dyno in the form of amps shown on the Classic's display, and a speed reading in the form if input volts on the Classic's display, and a hp reading in the form of real time watts. Subtract out the losses in the electrical equipment and we get brake power at the flywheel.

As you can see by the various power curves I have for wind turbines, I can make a wind turbine run any way I want with a Classic controller on it. I can do the same with a piston engine driving a generator.

Now we get the meat of the issue - and why you will not match a Classic controlled gas or diesel DC generator with a unit that is direct hooked. And why you can't match a Classic controlled wind turbine with one that is direct hooked to the bank. Ohm's Law is the determining factor. And the biggie version of Ohm's Law is I^2R power dissipation losses.

Let's consider a generator with a .5 ohm stator charging a battery bank at 60 volts. A permanent magnet generator develops a fixed amount of voltage for every rpm it turns because it has no variable field. The only thing that affects this is reactance losses in iron cores, but that's a different issue. So if this generator develops 80 open volts at 2,200 rpm, at 3,600 rpm it will develop 131 open volts. In order to get amps from this generator we have to "clamp" it to a lower (loaded) voltage.

OK, so let's try to charge our battery bank at 40 amps. With the direct hooked setup with the engine running at 3,600 rpm the generator is going to try to push 142 amps from the stator when you hook it up to the 60 volt battery. The engine won't maintain speed and it will lug down. When it lugs down we lose speed and have to increase torque. The balance will be found at 2,200 rpm - that's where you'll get 40 amps and the stator will be dissipating 800 watts. The power input requirement to that generator is 3.2 kW, 4.29 hp, or 10.24 lb-ft torque @ 2,200 rpm. The power efficiency of the generator is 75% - 25% of the shaft power being fed to it is converted directly to heat

With the Classic controlled unit, I can "clamp" the generator at a higher voltage of 120 and only require 20 amps from the generator. This requires an engine speed of 3,575 rpm. The stator is dissipating 200 watts. Shaft power requirement is 2.6 kW, 3.48 hp, or 5.11 lb-ft torque @ 3,575 rpm. The power efficiency of the IDENTICAL generator at the same power output (2.4 kW) goes to 92.3%.

Now - with the Classic I can adjust this to whatever I want to achieve the best brake fuel curve/generator efficiency combination just by pressing some buttons because it's a dynamometer. You can try to wind a generator for a direct hooked setup that's most efficient at peak output, and then you end up with too high of a engine speed requirement to get to the minimum 60 volts required for charging, meaning you'll never be able to idle the engine to provide charging current at the required 60 volts. Or you can throw massive amounts of materials at the generator and build a monstrosity that develops the required voltages with low enough resistance to get decent power efficiency - and end up with a small fortune just in the generator, not to mention an incredibly big and heavy unit.

No matter what you try to do with a direct hooked generator you can only tune it for one specific output at peak efficiency and live with a reduction in efficiency on each side of that. I will beat you with a Classic controlled one every way from Sunday with a generator that never falls below 90% power efficiency from cut-in to full rated output, and live with a very small conversion loss in the controller. Your best attempt at matching the best brake fuel curve to output with a direct hooked generator will be defeated by the increase in electrical efficiency I can get with the Classic with the same amount of fuel burned. There's a reason utilities use high voltage transmission lines stepped down to terminal voltages with transformers instead of generating 240 split phase right at the power plant.

I'm ALWAYS up for challenges. I'll build mine, you build yours, and we'll get together and run 'em with some test equipment and see who wins. We'd have to establish some baseline rules:
- that we both have to use the same engine - I'd propose a Honda GX200 because they're cheap and readily available
- use the same wire run from the generator to the battery bank - I'd set it at 20 feet to give the direct hooked unit a decent chance
- use a 24 volt battery bank (although I'd like to point out I can switch my setup to 48 volts by pressing some buttons on the Classic and loading a different curve for it)
- we can each use whatever generator we feel is necessary to do the job

The challenge is to simulate an off-grid cabin - we're going to charge a 232ah 24 volt battery bank (4 Trojan T105's) that starts out at 50% SOC, with a constant 1,000 watt load on the bank, to float, and see who can do it on the least amount of fuel. And once the generator is started you can't touch it - it has to do the job from start to float, and shut itself down (I'm just using the Classic's AUX 1 ON in Float to shut the generator down), without any intervention from a human. And all thru this the DC genset will be required to maintain PRECISE temperature compensated charging parameters to insure longest bank life and battery care possible in the long term.

That $650 for a Classic is starting to look pretty cheap when you want a REAL DC genset, huh?

And in the end we both end up with a DC genset for our homes, have a lot of fun, and have an excuse to drink beer.

I'd LOVE doing that. Wanna do it?
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Chris

Re: 48VDC generator head

The only thing is - I've never seen a wound field generator of reasonable size, cost and weight that can match a PM one for flux in the air gap. So that means higher resistance in the stator winding no matter what you do with a wound field. This is evidenced by Vestas, even though they use gearing in their wind turbines, have gone to permanent magnet generators with power electronics in lieu of the old wound field.

One of the "bad" things about PM designs is that the conventional iron core, or laminated electrical steel cores, that are used in traditional wound field generators tend to have some serious reactance issues with the extreme flux from a PM rotor. Those cores become saturated very easily with the powerful flux from neo magnets.

Even the most powerful wound field generators only have less than half of the airgap flux that modern PM neo magnet rotors can provide.
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Chris

Re: 48VDC generator head

inetdog wrote: »

(BSFC maps, for example) :-)

Brake Specific Fuel Consumption (in the old days when I got my mech engineering degree - lbs/hp/hr - these days the metrics are used). It's used on the dyno to predict and map engine fuel consumption vs power output. It is basically a function of the torque rise curve and thermal and volumetric efficiency of the design.
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Chris