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Author Topic: ST-3 , ST-5 or some other gen for 6/1?  (Read 6169 times)

jedon

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ST-3 , ST-5 or some other gen for 6/1?
« on: October 05, 2008, 10:15:51 PM »
I'm planning on charging a 48V bank of golf cart batteries off a 6/1 through an Outback VFX3648, which is the right generator to get?
An ST-3 matches the 6/1 output but I see a lot of people running an ST-5 instead. Is there a disadvantage to running an ST-5 instead of an ST-3?
GeneratorSales.com bundles Italian made Mecc Alte 3KW units with their 6/1's but they are a little more expensive, is it worth it?
Thanks!
-Jedon

Tom

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #1 on: October 06, 2008, 01:52:17 AM »
I'm running a 6-1 ST5 charging a 48v battery bank through a pair of vfx3648 inverters. My engine will run clean, once warmed up, putting out a steady 3120 watts. I've run up to 3400 watts, with a bit of black smoke. So it seems the 3KW head is a bit undersized. Also the stored energy in the flywheels will allow surges to quite a bit higher than 3KW. So I'd suggest you go with a 5KW head.

On my inverters I was disappointed to to discover that a feature I consider essential, generator support, is not currently enabled. What that does is combine the inverter and generator outputs to support larger loads than either could alone. Since I'm using 2 inverters I only have 13 amps per leg when on generator power. When I turn on the microwave it will draw the voltage low enough that the inverter/charger will trip out on the low voltage setting (108V) and go into inverter mode until the generator speeds back up. It then starts the cycle over again. If I had a 3KW gen head this problem would probably be much worse.

If you haven't purchased outback inverter yet, the xantrex sw series inverters do have generator support built in.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

jedon

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #2 on: October 06, 2008, 07:36:29 PM »
Tom,
Thank you for the info, this is very interesting to me.
I assumed the inverter always drew from the batteries and the generator charged the batteries having them act kind of like a capacitor when the generator is being run, handling peak loads.
Is your microwave situation happening because the batteries are low? Or is the inverter sensing enough power input that it ignores the batteries?
I was drooling over the SW6048 but didn't want to spend the $ for it yet.
-Jedon

assiduous1

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #3 on: October 06, 2008, 11:54:09 PM »
When I turn on the microwave it will draw the voltage low enough that the inverter/charger will trip out on the low voltage setting (108V) and go into inverter mode until the generator speeds back up.

Tom... I'm missing something here.  Unless you've got a lot of stuff running, the microwave (~1500W) shouldn't bring your voltage down to 108V.  That doesn't seem possible unless your batteries were really discharged and sucking up a bunch of juice.


Tom

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #4 on: October 07, 2008, 12:03:05 AM »
With the Out back it is an either or situation. The problem is not because the batteries are low, they have never been below 80%, but because I am overloading one leg the generator while the other is fully loaded.

What the Outback inverter does is set the max amps for charging. In my case I have it set to 13. As a load is added to that leg of the service the inverter cuts back on the charging amps until it is down to 0. From that point on the load is just passed on to the generator, so if it goes to 20 amps it just drags the voltage down until it kicks out at 108v.

When I planned the system I went with the 6-1 ST5 to keep the generator fully loaded most of the time. Had I known the issues with generator support on the Outback inverters I would have bought the SW inverters. They are not really that much more $ and do have some nice extra features for generators.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

MacGyver

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #5 on: October 07, 2008, 01:30:45 AM »
Tom, it sounds like you would benefit from a transformer like I used to balance the 2 legs.
I works amazingly well...
Steve

JKson (PS) 6/1 'roid & ST 7.5

MacGyver

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #6 on: October 07, 2008, 01:54:12 AM »
I'm planning on charging a 48V bank of golf cart batteries off a 6/1 through an Outback VFX3648, which is the right generator to get?
An ST-3 matches the 6/1 output but I see a lot of people running an ST-5 instead. Is there a disadvantage to running an ST-5 instead of an ST-3?


IMO, if you are ONLY going to use it to charge batteries, then the ST-3 is probably quite adequate.
If you are going to use it to drive loads directly, especially large motors and such, then it *may* be better to go oversized (ST-5) to handle starting loads better? I don't know.
Where it IS handy to have a larger generator (ST5, ST7.5) is when you are directly driving your house in the standard N. American 120/240 mode with the ST's windings in series. Loads may be way unbalanced and you may find that one winding on an ST3 is at max amps, while the other winding is doing nothing. So you can only use 1/2 the available power from your 6/1 without burning up your ST. A larger unit lets you run unbalanced loads without fear of damage.
Steve

JKson (PS) 6/1 'roid & ST 7.5

Tom

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #7 on: October 07, 2008, 02:26:05 AM »
With the Out back it is an either or situation. The problem is not because the batteries are low, they have never been below 80%, but because I am overloading one leg the generator while the other is fully loaded.

What the Outback inverter does is set the max amps for charging. In my case I have it set to 13. As a load is added to that leg of the service the inverter cuts back on the charging amps until it is down to 0. From that point on the load is just passed on to the generator, so if it goes to 20 amps it just drags the voltage down until it kicks out at 108v.

When I planned the system I went with the 6-1 ST5 to keep the generator fully loaded most of the time. Had I known the issues with generator support on the Outback inverters I would have bought the SW inverters. They are not really that much more $ and do have some nice extra features for generators.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.

jedon

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #8 on: October 07, 2008, 05:07:45 PM »
Tom, thank you for the extra info, I'll make sure not to do the same thing you did!

MacGyver, could you give some more details about how a transformer would help and where it would fit into the system?

Thanks!
-Jedon

MacGyver

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #9 on: October 07, 2008, 06:15:37 PM »
MacGyver, could you give some more details about how a transformer would help and where it would fit into the system?


I used a transformer to help balance the loads on my 120/240 system.
Here's a whole thread about it, including photos and connection diagram...

http://listerengine.com/smf/index.php?topic=3480
Steve

JKson (PS) 6/1 'roid & ST 7.5

Tom

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Re: ST-3 , ST-5 or some other gen for 6/1?
« Reply #10 on: October 07, 2008, 09:40:15 PM »
Steve,

I may try the transformer, after the final inspections are done. For now turning the microwave down to 80% power solves the problem.

The other solution I'm thinking about, that will also eliminate the flicker, is converting the ST5 into a 60VDC generator. That way I could just charge the batteries directly and it might be a bit more efficient too.

Then again perhaps by the time I get ready to do something Outback may have that feature implemented and a firmware upgrade makes it all good.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.