Bulk-Absorption Charging Voltage

[joraz]

2 Concord 8D (258 AH each)
Freedom 25 Inverter-Charger (130 amp)
Trimetric 2025 Gauge

I'm dry camping and charging my batteries. They were 30% discharged. My Concords call for 14.2-14.4v absorption and 13.2-13.4v float. My charger (20 years old) is set as close to those numbers as I could get at the wet cell cold setting which is supposed to yield 14.4v bulk-absorption and 13.5v float.

I just started my generator (10K) and see that the charger is only putting out 13.5 volts and 47.7 amps. (same after a half hour or so) Shouldn't I be seeing the maximum bulk voltage right now?

While waiting for some input an hour has passed. The charger is now supplying 14.1v, still substantially less than the 14.4 I had expected.
Thanks.
jor

[joraz]

UPDATE from OP

Well, I finally got to the RV today (painting my house). Anyhow, as you will recall I was concerned that my 130 amp charger wasn't providing the necessary amperage to my two 8Ds. My Trimetric indicated it was only hitting them with 50 amps or so even when the batts were 30% discharged.

Anyhow, I ran the microwave and other stuff today with the inverter and reduced the batts state of charge to 89%. Then I plugged in. The Trimetric showed 50+ amps. Then I put an ammeter on the charger and noted over 100 amps. Same at the batteries. So... it looks like my whole problem is with my meter. Have to do more checking now. I'm pretty certain I have it all wired correctly but you know how that goes. It will probably end up to be user error. I'll post when I have the solution.
jor

[pnichols]

Referring to the two o'scope photos above .... I wouldn't say the PD was bringing the Onan to it's knees. The EU2000i isn't doing so good either. For both generators, the current sine wave tops and bottoms are getting flattened, and both voltage sine waves are terrible. The PD is definitely presenting a screwy load to both generators.

For informational purposes, there's an excellent concise summary by Wayne Dohnal in this forum thread:

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25119121/srt/pa/pging/1/page/2.cfm

Here's a quote of Wayne's comment from that thread:

"It has been a long time since I learned this stuff and my explanations probably aren't the best, but here's a shot at it. The only pure form of alternating current is the sine wave. Any other waveform is composed of multiple sine waves added, or combined together. One of the worst waveforms, a pure square wave, is made up of an infinite number of sine waves added together. In the distorted generator picture, the principal component is a 60 Hz. sine wave. The distortions mean that there are additional sine waves at other frequencies, and lower amplitudes, added in. These other-frequency sine waves are in most cases undesirable, resulting in higher transmission losses (wires and equipment run hotter), emission of radio frequency interference, and in some cases the connected equipment not working right. As others have said, almost all electrical devices have no problem whatsoever with the distorted waveforms from small conventional generators. Problems are really rare. The one I've heard most often is the timer on some microwave ovens not keeping correct time because of the waveform distortions. As a comparison, some problems are seen with "modified sine wave" inverters, whose output is closer to a square wave. This waveform is much, much dirtier than what comes out of the generators, yet many RVers have 100% success with it."

[pianotuna]

Hi,

Thanks Salvo.

Back in the days when I'd use double conversion with the 2500 watt Cobra MSW inverter the PD9140A would never go beyond about 34 amps. Voltage would drop from 14.4 to about 14.1. The specifications say it draws 600 watts but I have measured 723 watts (kill-o-watt reading). I don't remember the shore power voltage when I was testing.

[Salvo]

Not sure if Wayne tested the PD from shore power. The waveform would look similar to the 1000W Honda; sinusoidal with a flat top.

The PD brings the 3600W Onan down to its knees. It can't handle the very high current burst. The PD has a design flaw. Say you have a 800W PD. The converter pulls no ac current from the line until the sinusoidal waveform is near the top if its peak. Then, all of a sudden it wants all 800W! That means over 30A are demanded from a power plant that's not capable of providing that much current. See the current plot that looks like a lot of middle fingers? That's why you see the flat top, the power source can't provide that much current and the voltage can't rise. As a result of the flat top, the PD input peak charge capacitor doesn't get enough voltage. Hence the PD never goes into current limit (max current) during boost.

The Onan shouldn't have such a large flat top as we see here. Something gets scrambled and it goes berserk.

[Salvo]

dp

[MEXICOWANDERER]

Looks a lot like my EKG's

I got a boatload of guffaws and chuckles when I spent 2-1/2 times the amount for a KATO generator than what a LIMA or Stamford Newage would have cost. I guess the latest rage is industrial size Chinese generators that use 48-volt alternators powering large inverters. I prefer 1,200 RPM steady state.

Boy a magnetron would gag on that waveform above. Big Onans are pricey. Their control circuits look like they were conceptualized by Timothy Leary. Then there is the Generack-ack-ack-ack.

Some @#$/\&! Stole my recording 3-phase power quality analyzer several years ago. Yotta see what a 250 horsepower ice-plant motor startup does to power "quality". ¿560 degrees lag? Scope screen looks like a plate of spaghetti.

[pianotuna]

Hi Salvo,

Did Wayne happen to test against shore power too?

[Salvo]

pnichols wrote:

Salvo wrote:
Wayne D proved it. You read it. I believe he even had scope plots.

Do a search if you don't recall.

It's waveform sure looks like a sine wave (but with steep sides) to me.

Here ya go.



eu2000i driving the PD6160A as its only load. Voltage plot on top, current plot below.



The Onan under same conditions.

And that's why the PD does so poorly with the Onan. It's more like a square wave than sine.

[MEXICOWANDERER]

Read up on the subject of LC loading of utlility generators. Better yet write to Lima or Kato and ask them. Rectified alternators share the same issues. A rotor whose pole pieces differ in spacing or clearance suffers similar distortion as rotation saturates the stator unevenly. Many times it is NOT the primary harmonic that causes damaging waveform architechure but 2nd and 3rd harmonics. Even the MU value of stator laminations can worsen waveform distortion.

[pnichols]

Salvo wrote:
Wayne D proved it. You read it. I believe he even had scope plots.

Do a search if you don't recall.

Continuing just a little bit more off-topic, here's the thread that Sal is probably referring to showing a couple of generator output waveforms, one of them being that of an Onan Microquiet:

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25119121/srt/pa/pging/1/page/1.cfm

It's waveform sure looks like a sine wave (but with steep sides) to me. Read the whole thread to see what some posters say about why the Onan sine wave output appears perhaps not "perfect". Some comments state that it's most likely the quality of non-resistive loads being placed on it that cause the distortion in it's output waveform.

I suspect - during boost mode and bulk mode battery charging using chargers with poor power factors - that the Onan output curves will distort.

[Salvo]

Wayne D proved it. You read it. I believe he even had scope plots.

Do a search if you don't recall.

[pnichols]

Salvo wrote:
It's a modified sine. It's not an inverter gen. Wayne discovered this.

Sal ... with all due respect ... prove it.

I no longer have my "Electrical Machinery" textbooks but as I recall, a spinning shaft generator "must" output a sine wave. Common sense-wise and intuitively this seems right, too.

Nevertheless, I'm open to an education on this regarding how Onan has managed to change (if they have) a rotating shaft's smooth going-up/going-down voltage waveform (sine wave) into a discontinuous voltage waveform (modified sine wave). Again ... a noisy sine wave from an Onan I can buy ... but I don't understand how Onan can put out a waveform that is discontinuous.

By the way, note the link earlier that was given above showing oscilloscope screen shots of so-called perfect sine waves coming from some types of equipment. They consist of many, many very small steps (256 or more), attesting to the fact that they're of a digitally derived origin. A rotating shaft derived sine wave is continuous (but maybe containing noise), with no steps.

P.S. I apologize for going/staying off-topic on this but I can't imagine that Onan has been putting out junk waveforms ... either since day-one, or since Cummins took over ... especially at the prices those things cost. I have another rotating shaft generator that will not run some of our RV's appliances ... that the Onan will. That's a another head-scratcher (maybe grounding related).

🙂

[NinerBikes]

Criminy, guys, what kind of can of whoop azz did I open talking about sine waves on generators?

[Salvo]

It's a modified sine. It's not an inverter gen. Wayne discovered this.

pnichols wrote:

Salvo wrote:
Even if you got 120Vrms but don't have a pure sine wave (like Onan Microquiet gen

A bit off the OP's topic, but I don't understand ... how can a rotating shaft generator like the Onan not have a perfect sine wave shape buried inside it's AC output voltage curve?