Voltage drop booster for AC Generator

I gather you are using the AC output of the generator, and not a DC output. (Typically the DC outputs, when present, are of much lower wattage, because they are current-limited.)

You say that the generator is capable of running the charger. Do you mean that the generator rating suggests that it can run the charger? Or have you actually had the charger running somehow on the generator? Is the charger cord short and of adequate wire gauge? Connections sound?

Capacitors do not store AC, so I can't think of anything between the generator and charger that would help. Having some form of soft start on the charger would help, but that would mean rebuilding the charger.

There are complicated jury-rigged arrangements that could work, (battery and large inverter, etc) but they would cost about as much as a larger generator.

Thanks for the comment. Yes we are definately using the AC output. We have run the charger on the generator. This has been done by lifting the battery voltage to almost fully charged voltage with another source. The surge under these conditions is less and we have been able to start the charger on the generator. We can then remove the other DC voltage source, apply DC load to lower the voltage of the batteries and the smart charger will operate at 100% output quite comfortably. Once running the generator will run the charger without problem indefinately. AC power lead is only 1 metre long and has 10 amp rating.

Is the input voltage to the charger 120Vac or 240Vac?

240Vac

I have a suggestion. Only an idea.

Generator is self excited as usual.

Possibly the charger is thyristor controlled. Thyristor, no matter if the primary or secondary windings of the charger, detoriating the output waveform of the generator. Therefore self excitation, as well as the voltage regulator of the generator is being negative impressed from its self output.

Please make sure if it is not an overloading problem. Then try some resistive load, (Such as 150W) at the output of generator, to be fed together with the charger at the startup to correct the waveform. Then after you can switch it off.

If only for a short time why not insert the 80ohm inrush resistor which you can bypass with a power relay after a timer on delay. You can size the resistor power by the time needed but if its 10s or less maybe 100W should be OK.

Just a thought,

If your "system" runs after the battery has been charged from another source( lower draw) then borrow a 1500 watt gen set and give it a try. this should tell you the simple answer you are looking for. Note - the input power quality to the charger seems to be the issue. the charger may be drawing twice its ratting to get started . also how many batteries are you charging. 1 or a bank of 2,3,4+. if it is more than 1 then the load on the charger will seem more like a "short" causing the instability and protective shut down. in the end a larger gen will remove all issues as well as give you capacity for the big screen TV and DVD player~

If any generator set is overloading, the first indication appears mechanically and at the descelerating speed of the engine. (even inrush, motor startup, and other temporary overloadings)

However the friend in his first message, stated that no speed loss is resulting. This allows me to think this is not a power rating problem. The matter is not an overloading.

In my opinion, it seems like an excitation problem. Most of those small (Brushless) alternators are not having a separate permanent magnet exciter. They are using "Third Harmonic" method. The third harmonic (say 150Hz -180(Hz) from output of the generator is fedback by a capacitor, to the exciter windings and therefore alternator armature poles are magnetically excited, via the Voltage regulator.

Fast switching components (Such as thyristor controllers in the smart charger) are the croppers. Cropping the sine wave forms and also creating many harmful new harmonics. The new harmonics are not in the sine wave form. Those new harmonics are reverted to the generator output. Compensating those harmonics is difficult.

In this new case of the load is controlled by the thyristor controllers, the third harmonic, used for excitation for the generator exciter is open for negotiations. It may be not available, or with wrong polarity, or not in the sinus form. Eventually no excitation in the generator may occur.

Since the smart charger is rated to 400 watts, this means the generator has some 300 Watt surplus power. Using this extra power to feed two 100 Watt incandesant light bulb, may be a solution, still to obtain a sinewave third harmonic at the otput of the generator.

Kindest Regards

Bob,

Have you tried to reduce the current limit of your "smart" charger? This should limit the inrush current to a reasonable value.

Another possibility is to add an suitable AC capacitor at the charger's input to improve the power factor. This is because thyristor controls regulate by shifting the phase angle of the trigger point. This produces a very bad lagging power factor when low voltage is needed. This is probably the case when the batteries are low. A 10uF 440V motor run capacitor should do it. The risk is that it may increase the di/dt seen by the thyristors and damage them if they don't have an internal choke. Make sure that there is a step-down transformer before the thyristors. This will act as a di/dt limiting choke. You might need to disconnect the capacitor when the battery is almost fully charged if your generator doesn't like leading power factor.

Good luck

You may find that attaching the charger without attaching the batteries at all may help, then attach the batteries afterwards. One at a time if more than one battery.

The resistor idea in the 240 line might also help.....

I guess the problem is the "sudden" load is too high for the excitation control of the alternator to handle correctly.

A larger alternator would be an easy fix.......

Thanks for all the replys. I'm also convinced it is a winding or excitation problem as there is very little decay in rpm when the charger attempts to load the generator. I have had a volt meter on the output voltage of the generator. Voltage is sharply killed (over 100 volts) without the engine really straining. When I first installed the charger it booted up on most occasions (batteries were fairly well charged however). At this time I had a 60 watt incandesant lead lamp attached for lighting the area. After the installation was complete this lamp has been removed and since then the charger will not boot. I have been of course trying to reduce load as much as possible but I'm sure the problem is worse since removing the lamp. Today I will try a larger resistive load in parallel and see what happens. Will report back!

Hi Bob.

As far as understand you have made the trial of 60 watt lamp and the charger booted up. And when you remove the lamp, the charger did not boot.

This is what I am saying in my messages. You need some resistive load connected parallel to the charger.

I will be eagerly waiting to learn your result with more resistive load. (Such as two 75 or 100 Watts incandessant lamp)

You can easily check the engine RPM speed loss against the case of overloading. However this will cost you an extra fuel consumption.

Regards.

In parallel may help, but the poster (and I) meant in series, with a switch or relay shorting across it, to allow the resistor to be switched out for full charging level......

Half right, half wrong Andy,

Adding the batteries in increments may well be a "get around" solution.

Adding resistance in the AC line will exacerbate the problem. Putting a resistance in the DC line would do it but it would have serious power dissipation (not practical).

This charger is probably powering a boat of 35' to 45'.

I would like to know what make of charger Bob is using. I suppose it is one of the cheaper brands as all the better models have a soft start feature. Additionally, better models have a power factor correction circuit. This may well have a bearing on the issue as the input of a switch mode battery charger, which this is likely to be, will have a very bad power factor and this corresponds to the OPs observation of low voltage without engine loading.

Try the charger manufacturer to see if the charger has a remote control to limit the current. Many good units have this as a feature for just this reason and to avoid tripping low power shore supplies.

Adding the parallel bulb may well help this situation, but it is only a work-around.

Best advice, get a better charger or upgrade the generator.

Kind Regards

Chas

I rate you as about half right and half wrong too....

As neither of us have enough information to be 100% certain of a fix.

Have a great day.....

Chas,

The charger is a Xantrex TC4012. I just looked up the manual and a remote control panel is available. One function on this remote ,that I just noted, that is not available on the charger control panel, is a % load limiting function. Limiting the DC output to say 80% may solve the problem. This may well be a cheaper solution than a new generator or new charger! The charger was not that cheap!

Regards

Bob

Hi Bob,

Yes, the remote should do the trick, Just start it all up on minimum then key in the extra output.

regards

Chas

I believe you are correct that small generators do not have enough copper and armature mass to handle the inrush current, plus the voltage regulators are not that sophisticated. The Xantrex charger is the problem. It is too smart. Unless you are doing deep discharge/charge cycles with rapid recovery needed, a smaller charger may be your least expensive solution. Or talk to Xantrex and see if the minimum input voltage window can be adjusted?