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Old 17-10-2020, 13:21   #1
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Westerbeke 8.0BTDA - Voltage Drop Under Load

Hello All,

Looking for advice from someone who knows this particular genset VERY well. It's a 2003 Westerbeke 8.0 BTDA with just under 3000hrs.

Generator is in good condition and operates well, with one exception. The genset loses about 10v under load per 2KW of power produced. So at 50% load, it loses about 20v.

The reason it is losing voltage is because the genset is slowing down from 61.5hz to about 59Hz.

I have been through the no-load adjustments recommended in the manual. I don't believe the motor is weak as I can *crank* up the RPM speed or the voltage and the engine has no problem driving it. The problem is consistency.

If I get the no-load voltage and Hz at 121-124 and 61.5Hz, then loaded at 50% the voltage has already dropped to 108v.

If I set the voltage and engine speed higher so that it's in an acceptable range when loaded, then unloaded, it's much too high.

My instinct is that this must be something to do with the governor....perhaps it needs replacement or adjustment, but other than changing the RPM, I'm not sure what adjustments I could make.

Does anyone have experience with this issue on this particular genset? Unfortunately, Westerbeke tech support has not been helpful in diagnosing the issue.

Thank you in advance.
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Old 17-10-2020, 14:33   #2
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Do you have the Technical Manual?
Have a look at the troubleshooting table (attached), and go from there.

If you want to PM me an email address, I can send you the manual (it's 13mb). Or if you have an idea what the issue is, I can copy the relevant part out of the manual and post it here.
Attached Files
File Type: pdf page 1 troubleshooting table.pdf (94.3 KB, 12 views)
File Type: pdf page 2 troubleshooting table.pdf (96.0 KB, 6 views)
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Old 17-10-2020, 16:04   #3
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Thanks. I have all the manuals and have gone through the troubleshooting guide.

Unfortunately, the only thing in the guide that would describe the symptoms, would be an overloaded unit, but as I said initially, even at 50% load, the genset doesn't seem to hold it's RPM's. It's dropping about 60 RPM at 50% load.

I suspect a problem with the mechanical governor, but I'm not well versed enough in what might need adjustment in the governor like the weights or spring replacement etc. to know where to start.
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Old 17-10-2020, 17:15   #4
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Does your generator have the optional electronic governor? Otherwise, it's just the adjustment screws and shims. Sounds like it might be in spec:

Quote:
e. Load the generator to the rated amperage output
corresponding to the hertz speed of the generator.
Rated Loaded Speed
60 hertz: loaded speed, 58.5 - 59.0 hertz
50 hertz: loaded speed, 48.5 - 49.0 hertz
The lowest acceptable voltage at full rated output
(amps)
60 hertz: 108 - 11 0 volts
50 hertz: 205 - 210 volts
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Old 17-10-2020, 18:51   #5
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

On my 4.5 kw Westerbeke, I always had a problem. To get it to run at a nominal 120 volts when loaded by the 80 amp battery charger, I had to set the no-load voltage up to 132 volts. That required changing the over-voltage threshold for the charger to get it to turn on. I suspect that the whole mechanically regulated Genset idea just doesnít regulate very closely. +/- 10% is 108-132 volts. Being exactly 60 Hz across that range is going to be tough. You could probably get closer regulation with one of the newer, fancier electronically regulated Genset , but only at the cost of more complexity.
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Old 18-10-2020, 08:28   #6
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Thanks Bycrick. I've tried upping the no load voltage in the past, but my no-load to full load voltage drop is about 40v. I've ended up making sure I just don't load up the genset very much to avoid too much voltage drop.

It's just too big of a swing to subject electronics to, and far more range than a properly working mechanical governor should allow.

I'd still love to hear from someone who has experience with this particular mechanical governor. Some of the later units were shipped with an AVR (automatic voltage regulator), but my wasn't one of them.



Quote:
Originally Posted by Bycrick View Post
On my 4.5 kw Westerbeke, I always had a problem. To get it to run at a nominal 120 volts when loaded by the 80 amp battery charger, I had to set the no-load voltage up to 132 volts. That required changing the over-voltage threshold for the charger to get it to turn on. I suspect that the whole mechanically regulated Genset idea just doesnít regulate very closely. +/- 10% is 108-132 volts. Being exactly 60 Hz across that range is going to be tough. You could probably get closer regulation with one of the newer, fancier electronically regulated Genset , but only at the cost of more complexity.
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Old 18-10-2020, 09:04   #7
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

If you’ll allow a little speculation. Have you read out the actual change in engine speed between no-load and full-load output? That would maybe tell you whether or not it’s a mechanical problem (governor?) or electrical problem. I had one Genset problem where the bridge rectifier had one of the four diodes open up. This reduced the field current and produced low output and low load capacity. The only "regulation" is the result of the Genset core reaching magnetic saturation. On mine, the maximum output at rated RPM is actually set at the factory by putting shims between pieces of the generator core.
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Old 18-10-2020, 09:07   #8
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Mechanical governors are calibrated for 3% speed droop, or a 3 % change in frequency with a 100% change in load.
Voltage regulators can operate on volts/cycle or voltage control mode. A 3 to 6 % range is normal for a 100% load change. This voltage is being measured at the generator terminals.
Most generators have a dedicated electronic card for voltage control. Your voltage regulator is out of cal and the mechanical governor is performing itís function properly. The voltage control circuit is at fault.
Poor brush contact, on generators with brushes, can give the same symptoms
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Old 18-10-2020, 09:22   #9
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

I have a much older Westerbeke WMD-8 with a similar problem. It would run at the correct speed and voltage under no load, but when loaded it would slow and with enough load die. The problem was a fuel filter on the engine. I have external filters Racor filters, but this is a small filter that is part of the genset motor itself.
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Old 18-10-2020, 10:42   #10
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Fuel filter. Sounds like it is worth changing it.
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Old 18-10-2020, 10:49   #11
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Quote:
Originally Posted by lorenzoj View Post
Mechanical governors are calibrated for 3% speed droop, or a 3 % change in frequency with a 100% change in load.
Voltage regulators can operate on volts/cycle or voltage control mode. A 3 to 6 % range is normal for a 100% load change. This voltage is being measured at the generator terminals.
Most generators have a dedicated electronic card for voltage control. Your voltage regulator is out of cal and the mechanical governor is performing itís function properly. The voltage control circuit is at fault.
Poor brush contact, on generators with brushes, can give the same symptoms
I agree with Lorenzoj that the governor is doing its job because your frequency is only dropping to 59 Hz under 50% load. Since the engine is running at the right speed but the generator isn't producing enough power, its got to be a voltage regulation issue.

These kind of problems are tough to diagnose because there are a lot of pieces to the puzzle, and to test some of them, you have to remove the electrical end from the generator. For example, the diodes on the armature that rectify the field voltage have to be unsoldered to test them, and that can't be done with the armature in place. You can test a lot of the other pieces of the excitation system without taking the thing apart, but yours sounds like a subtle problem that will require expertise and time to diagnose.

Here's a thought for you: Westerbeke sells rebuilt generator ends. The last one I installed was about $2300, also for an 8Kw generator. If you were my customer, that's what I would advise you to do.

Best of luck.
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Old 18-10-2020, 11:12   #12
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

I donít know about the 8kw Genset. But my little 4.5 has two fuel filters on it. One actually looks like a small fuel filter with a metal basket held onto the base with a retaining ring. The second filter is "hidden" inside the fuel pump, and accessed by taking the bottom off the fuel pump. Neither one of them is very big, so they might well be dirty if you havenít looked at them for a while.
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Old 18-10-2020, 13:15   #13
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Lorenzo/Byrick,

Thank you for the thoughtful replies. I agree with most of what was suggested up to your conclusions.

Your comments about probable/acceptable drop for a mechanical regulator are correct. A 3% drop at full load would be a Hz change of 1.8 HZ. Which from 61.5-62 should leave me around 60Hz at full load. This would be more than acceptable and should have an accompanying voltage drop of perhaps 10v or so.

At full load I'm dropping to 56Hz and 40v which is like a 10% loss of RPMs.

With these gensets, voltage is tied to Hz. Unit slows down, Hz drop AND voltage drops. Maintain Hz and voltage is also maintained. While these parameters can be individually adjusted in a no-load state, once running, they are tied together.

To any who have suggested it, it's not a fuel flow problem. Filters are clean and engine is lots strong and will easily produce more power, it's a speed *maintenance* issue, not a power production issue.

Does anyone have any actual experience with the governors on this particular model of generator?


Quote:
Originally Posted by lorenzoj View Post
Mechanical governors are calibrated for 3% speed droop, or a 3 % change in frequency with a 100% change in load.
Voltage regulators can operate on volts/cycle or voltage control mode. A 3 to 6 % range is normal for a 100% load change. This voltage is being measured at the generator terminals.
Most generators have a dedicated electronic card for voltage control. Your voltage regulator is out of cal and the mechanical governor is performing itís function properly. The voltage control circuit is at fault.
Poor brush contact, on generators with brushes, can give the same symptoms
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Old 18-10-2020, 15:39   #14
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

Page on the governor (pg 37). Personally I'd do the exciter rotor check first (pg 102) (no need to de-solder anything). Attached
Attached Files
File Type: pdf pg 37.pdf (140.6 KB, 6 views)
File Type: pdf pg 102.pdf (73.8 KB, 5 views)
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Old 19-10-2020, 15:56   #15
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Re: Westerbeke 8.0BTDA - Voltage Drop Under Load

This is what I'm after! Thank you.

Quote:
Originally Posted by Lodesman View Post
Page on the governor (pg 37). Personally I'd do the exciter rotor check first (pg 102) (no need to de-solder anything). Attached
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