Today I did a full cycle run of the Kubota Generator using the new Arduino based alternator regulator and throttle controller. And here is a graph from the debug log data that was produced:
Two things to notice:- See how flat the Watts line is during Bulk phase?
- Likewise, notice how the Amps line drops during the Bulk Phase?
This is the result of the key goal for the project - maintaining a constant load on the driving engine. As the battery voltage increases we need to lower the Amps delivered in order to maintain a constant Watts load delivered (and pulled from the Kubota engine). Almost without exception, no alternator regulator is able to do this. (I only know of one other, and it costs a LOT of $$. Like a couple $1,000). I want to maximizing the the capabilities of the generator when it is running, and hopefully reduce overall run time.
One can also see the engine RPMs being managed - as the battery approached full charge, the amps dropped off quickly and the resulting load on the engine was reduce. So we slowed the engine down. Need to work on that fuzziness in the Field PWM on the right.
You can see more here: http://smartdcgenerator.blogspot.com/
I'm impressed.
ReplyDeleteLet me see if I understand what you have done. I believe most multi-step alternator regulators use maximum alternator output until the transition from bulk to acceptance, and under that scenario because voltage is steadily increasing the work done by the alternator (watts) is steadily increasing. It seems like this would be good if the energy available to drive the alternator was greater than necessary for charging, such as an engine driven alternator on the main propulsion engine. And I am under the assumption that this charging routine would be used to charge the batteries in the shortest amount of time.
It appears that you have chosen to stabilize the load on the charging engine at the expense of time, at least in the bulk stage, and furthermore, to reduce the engine output when charging loads are reduced.
Am I correct? If not, please explain. And if so, what are the other advantages (besides stabilized engine loading) that can be obtained?
Hello. And Thank you. Glad to see someone is watching so close!
ReplyDeleteYou got it almost right. All that you said in the 1st paragraph is spot on, and in the 2nd you are right that I am stabilizing the load - but the result should be to reduce, not increase overall generator run time. And here is why:
In the case of using the main engine to drive an alternator there is a LOT of excess capacity in the engine, so the limit really becomes the battery and alternator - just as you pointed out in your 1st paragraph. However, with a small engine / generator project - we need to size everything around the peak-power point. In a 'traditional' regulator approach this would be the point where the system ends the bulk phase and enters the acceptance phase. It is when system voltage is highest, and the battery is accepting as many amps as the alternator will produce. It is the maximum load point for the engine, and one needs to make sure the alternator is small enough to not overload the engine at this critical point. More so: anything before that point will have lower system voltage due to the battery SOC, but fixed amps due to the alternator, and hence lower total watts / load. Anything after that point has fixed volts (due to the regulator), and reducing amps due to the batteries acceptance rate. On either side of that peak point there is less total watts being delivered, and hence less load on the engine.
What this project does is still size the system to the peak point, but by using a larger capacity alternator – and actively regulating the Amps – we are able to ‘Back Fill’ during the earlier parts of the Bulk phase. In the example above, when we are before the Peak Point and the system voltage is limited by the battery SOC, by using a larger alternator we can ‘up the amps’ some – the voltage stays the same (it is battery limited), and with the Amps increased we are able to bring the total Watts - and hence engine load- back up to the peak point. Side note: IF we had gone ahead an used this larger alternator with a traditional regulator we might have been OK at the beginning of the Bulk Phase, but once we got to the Peak Point we would be greatly overloading the Kubota engine.
And this is why the Watts line is flat during the entire Bulk phase – the controller is regulating the total watts being delivered at all times to ride on the max capability point of the Kubota engine. In effect, the limiting factor now becomes the capability of the Engine, not the capability of the Alternator. And by taking advantage of the previously wasted capacity in the early parts of the Bulk phase, total generator run time should be reduced.
Once we cross into acceptance phase, the battery becomes king – both in terms of voltage and the amount of amps it will accept. Hence the Watts begin to drop off. That I added full throttle control was a ‘feature creep’ of this project – seeing as I had a way to start and stop the engine via the throttle, it was not much more effort to control its speed.
And in the end – it is stabilizing the engine load that is THE advantage. But more so that we are stabilizing it a the peak capacity of the engine, taking advantage of all is ability during the entire Bulk phase. That was the primary driver for this project. The rest is just icing on the cake.
-al-