I looked again thru the Operations Manual for the DCX3000 and don't see anything close to a curve or specs as to what current limitations are imposed as a function of battery voltage. For 48v operation, the photo of the output connector shows 53.3amps at 52.5v. But that's it.
And we know that they default to zero output above 56v.
It's pretty likely that the current limit drops, probably linearly, from 53amps (at 52.5v) to Zero (at 56v).
So here's what happens:
· You head out into a high power demand scenario (upstream, against current, fast, etc.) and, wanting to save power, you fire up the genset. You're delivering 50amps from your generator but you're still running a 40amp deficit.
· You connect up the second DCX3000 which attempts to put out 50amps also. In response, the battery voltage rises. As the pack voltage rises above 52.5v, both generator outputs drop. The outputs will continue to drop until the voltage stabilizes.
To get both gensets to continuously put out 50amps each:
· You need to ensure your pack voltage stabilizes below 52.5v while both gensets are running and your loads are going.
A story:
When I was doing a 45-mile trip upstream on the Columbia River one day (back when I had 36v lead acid pack), I had my Honda EU2000i running and had 2 chargers plugged in---one was a 36v Lestronic and the other was a Vicor Megapac loaded with five (5) 48vDC, 4amp modules. At one point, my generator was throttling up and back, repeatedly. I looked into it and noticed that the Lester's output was going up, then down, repeatedly as was the pack voltage and the net current to the batteries. As I increased the boat motor's throttle, this effect went away. But I still didn't seem to get full current out of my Lester---it was only, say, 15amps, not 20amps. I increased the throttle some more, and voila! The Lester was up to 20amps along with the Vicor and I ran at this maximum all day. For me, what worked was to observe the NET CURRENT into the Battery Pack and to set my boat speed such that Net Battery Current == ZERO amps. And as long as the pack voltage was below the voltage where the Lester put out its maximum, I was getting maximum steady power from the genset thru the chargers. I didn't need to look at pack voltage until later when I found that I needed an extra 5amps to make the headway upstream that I needed. And so I drew a deficit, but it was manageable and I made it back with only a few spare electrons left…
-Myles
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Thursday, June 29, 2017 10:10 AM
To: electricboats@yahoogroups.com
Subject: RE: [Electric Boats] Re: Current 48 VDC alternator/generator options
Arden-
A couple points.
First, it's expected that the 2 DC-output gensets would share the load equally when paralleled. If that's not what you want or expect, then you'll have to modify one of the gensets to not throttle back with voltage or to somehow adjust or move its "load curve" higher.
Second, that "load curve"---as I understand the specs for the genset, there's no stated load curve---nevertheless, it definitely follows one. It appears that the 48v genset defaults to zero output below 42v and considers a battery FULL at 56v. Presumably, the genset will deliver FULL RATED CURRENT at the low end (42v-someV). What the generator does between the lower limit and 56v is anyone's guess. If it's like the Lestronic charger, the current will drop somewhat linearly with voltage. But then there's the fact that it assumes lead acid batteries and that it should put MAX power thru the Bulk charge voltage phase, then taper the current down when it approaches the max voltage. And there's the rub: Where does it start tapering? If they don't put it in writing, we don't know. As mentioned, the LESTER chargers start tapering right away and they taper towards 5amps or near zero instead of tapering according to keeping Max Power. IF (big IF) the DCX were to deliver Max Rated Power up to 56v, you'd expect about 30% drop in current from 42v to 56v, and with 2 gensets, you should get Full Rated power but with 60% max current. At 48v, you'd expect even more current.
So this is a bit strange.
Are your gensets rated for 48v Lead Acid or 36v?
If 36v, you shouldn't get ANY output above 42v from either genset.
Bottom Line: You deserve to know the load curve for the genset. See if you can get it.
-Myles
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
Sent: Wednesday, June 28, 2017 10:58 PM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Re: Current 48 VDC alternator/generator options
Myles,
Now that testing and practical use of the AlphaGen DCX3000 has been accomplished I can say that I can't seem to get two of them to spool up past 50 amps. A single unit will put out 50 amps but adding another running AlphaGen DCX3000 to the mix only lowers the current on both of the units.
They do function quite well and certainly extend the range but I still can incur an amp hour loss over time and I'm not happy about that as at times I may require 40+ amps on the negative side to run with conditions over and above what the generators and solar are bringing in.
Conservatively that limits my run time and gives me "X" number of hours at 40 amp deficit.
I'm currently sourcing out another Honda 2000 and a couple more 48v chargers.
I recently procured a Honda 2000 and am able to run a couple of my 48v Lestronic II 17910 chargers on it and produce 30 amps.
I figure if I had another identical setup to that I would save weight on the boat and always have 60 amps at my disposal. Combined with solar and I can then be inputting close to 90 amps back into the back. Therefore I could be fully charged in 4.5 hours.
Also I can motor most anywhere for 60 amps turning prop for 30amps a side on each of my outboards. I can pack over 20 gallons of gas on board so at that rate I can motor for a really really long time without incurring a major amp hour draw if needed.
Arden
Posted by: "Myles Twete" <matwete@comcast.net>
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