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Small torroid transformers - buy, or make up?


Antfarm
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Greetings, as part of my microhydro system I need to connect a 3-phase AC generator to my 48V battery bank.  I'm advised that as part of the connection I need 3 units of a 117Vac primary, 24Vac secondary transformer?  320W.  (See attached spec sheet)

I can get them from the USA but freight and tax are an issue.

Can I get them off the shelf locally, or can I get them made-up?

Thanks

 

 

 

732.242.pdf

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What are you connecting these generators to? If you use an inverter that has DC inputs, like a Sunsynk, I'd look at rectifying the 120VAC 3 phases and feeding it into one of the 2 MPPT inputs, that way, the inverter would take care of the batteries and obviously also generate the 220V or so AC that presumably you ultimately want...

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I have a victron multiplus inverter/charger. Ideally I'd like to feed in the power to an MPPT to charge the batteries and protect the kit from the turbine, but cash is a constraint as it seems I need a 150V MPPT. So thought to charge the batteries direct and have a clamp or diversion control to protect from overspeeding

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Well, yes and no, you may still need transformers to bring the voltage to something that the Victron can handle, but I suggest using the Victron, after all, else you need some extra electronics to monitor and ensure the batteries aren't overcharged/undercharged etc.

If you can bring the voltage into the range that the Victron is happy to digest, I assume it handles the charging of the batteries, then that would be 1st prize in my opinion. Now, I guess you need to visit the spec sheet of the Victron and figure out what it is happy with on the input end...

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Does the generator produce 117V or 234V ? (or the more normal 120V or 240V).

From the pdf you sent, the transformer can be wired in series for 234V or paralleled for 117V. 

If your generator is 234V then you don't need the 117V windings and just need a single 234V winding. 

I presume you would need the 48VAC output of the transformers.

You DONT need to get toroidal transformers - normal transformers will work fine. 

I agree with Kalahari Kat that you will need a (preferably MPPT) charge controller  to manage charging parameters such as charge current and voltage so that you don't damage your batteries from overcharging.

Because you are producing DC from AC you might need to put some smoothing capacitors in - but I am not sure of that. 

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The generator recommended to me is a 3-phase permanent magnet PMA-1112, which would have a no-load output of 235V at 2096 rpm. "We want 208Vac to work with the 120V transformers connected in wye which gives 27V for windings losses with current. ".

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overlap timing wise in posting...

I think the output from the 3phase Water genny is probably 117V close enough to 110/120V for America just not sure at what frequency this lot will generate 3 phases out which is also a bit of an issue, a transformer designed for, lets say American mains frequency, won't work properly or reliably with a long life here where we have 50Hz mains, in other words, a transformer is designed for a specific frequency 60Hz in America, 50Hz here and probably all of Europe, the transformer designed for 60Hz will not work too well at 50Hz, it will get a lot hotter at 50Hz than at its design frequency. The other way around, its less of an issue, thus a transformer designed for 50Hz will be a lot happier at 60Hz.

So, keeping this in mind, you should probably also do a bit of homework about at what frequency the 3phase genny will operate, this, of course, I assume depends on the RPM's attained, as long as its 50Hz or higher, that should not be a problem.

The smoothing caps shouldn't be needed at all, specifically if all three phases are full wave rectified and lets assume it operates at 50Hz (should be higher), then it really should create current/voltage peaks at 300Hz, unless I'm mistaken and possibly more, so I think you should be able to skip the smoothing end...

Wrote the above before seeing your post about the 235V at 2096rpm... what would the frequency be then, I wonder... not sure how to figure that, depends on the amount of magnets, I guess, it seems to be in star config, but without knowing the amount of magnets floating by per revolution, there's no way to determine the frequency. If you can guarantee 50Hz or higher, then using a transformer designed for 50Hz to get the voltage to a level your other equipment can handle should be ok.

Edited by Kalahari Meerkat
timing of posts...
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1 hour ago, Antfarm said:

The generator recommended to me is a 3-phase permanent magnet PMA-1112, which would have a no-load output of 235V at 2096 rpm. "We want 208Vac to work with the 120V transformers connected in wye which gives 27V for windings losses with current. ".

OK that information is useful. So it appears the generator phase to phase voltage is 208VAC. This works out to a voltage of 120V per phase to the neutral (star point). So you do need 120V input to the transformers. Good news is that you dont need to worry about getting a transformer specially wound for 117/24 volts. 

A transformer that has primary voltage of 240V with 2x 48V secondaries (wired in series) should work well. It is perfectly fine to drive a transformer at 1/2 the design voltage.  In other words a 240/96 transformer driven by you generator will then give you 120/48 which is the transformer you were looking for.  I reckon they show the option on the secondary as 24V or 48V so you could have a 24 or 48V battery pack in the system.

It does not matter if you run the transformer at 50 or 60 Hz according to the pdf you posted.

I would suggest you oversize the transformer to minimize losses and lessen the voltage drop across the windings.

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Thanks for the input @GreenMan, @Kalahari Meerkat, @P1000

So to summarise, I should get 3 of 240/96 transformers as they will do the job and are likely to be available off-the-shelf, rather than needing to be made up.  They do not need to be toroidal. Is this correct?

Ideally I should then feed the rectified power into an MPPT (150V).  If this MPPT is out of my budget then I need to go the load diversion/clamp route

The maximum power potential from the water head is about 600 watts, so what maximum power rating should these transformers have? I assume it's less than 600w as it's spread across 3 phases.

Any recommendations on where to get these in the Western Cape?

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Yes pretty much so but you would probably struggle to find an off the shelf 96 V secondary. 

So your best option is to get them wound for you. You could try SJ Andrews [email protected]

Your first post mentioned 320W so this is a motor application so we can assume PF of 0.8 so that would equate to a 400VA transformer.

The MPPT voltage rating that you require will depend on the max voltage you will get out of the secondary side of the transformer. Does the spec sheet state what the  max voltage is that you will get ? 

I assume you would put a bridge rectifier on the secondary of each of the transformers ?

Did they supply you with a schematic diagram that you could post ?

 

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