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Marcus20VT
Regular Member

Joined: 02/09/2008
Location: Wales
Posts: 49

Posted: 10:56am 16 Jun 2010

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Hi,
I've just bought a 300 watt 12-28 volt grid tie inverter from one nation renewables ltd.
The good thing about this unit is that it is cheap and has G83/1 certification for use in the UK
However, I have just read the small print on the unit, and it says that it shouldn't be connected to batteries as a DC power source.
This is a bit of a problem as I only have 2 small panels 112W and 15W and the minimum power intake is 20W - which won't happen very often with my panels. I was going to charge a battery system with the panels, and when fully charged I was going to connect it to the gti.
I would have thought a battery would be a good thing to use as a dc power source as, unlike the pv panels, the output voltage is fairly constant. So i'm a little confused why I can't use one - the small print says - "this will damage the inverter and void the warrenty".
Would this happen using a 12 volt battery as the voltage is near the minimum of the inverter spec. What would happen if I used a 24 volt battery as this voltage is at the higher end of the gti spec?
I have tried to phone one nation renewables, but they don't accept calls from my works phone system as it witholds our number!
Any advice would be much appreciated - thanks.

KarlJ

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Joined: 19/05/2008
Location: Australia
Posts: 1178

Posted: 11:58am 16 Jun 2010

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I hope it was cheap and i think it will be AOK IF it works, might need a certain voltage present to connect to the grid which a battery wont give.

It may not be able to handle the current a battery can deliver attach a suitably rated fuse before connecting it EG 24V 300W go for 10A and 12 V go for 20A (which i reckon would smoke it)

Karl

Luck favours the well prepared

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 12:37pm 16 Jun 2010

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Hi Marcus

As Karl said the battery will deliver more current than 300 watts and the unit nay be not be current current limited so if it blows the 10 amp fuse on 24 volts then you can put a active current limiter in series with it and set it to required amps. the link below will limit the current for you its a HHO cell limiter but will limit OK for your application, just be sure to set internal regulator to 12 volts so as not to let the smoke out.
http://www.alt-nrg.org/pwm-v2.html

All the best

Bob

Foolin Around

Robb
Senior Member

Joined: 01/08/2007
Location: Australia
Posts: 221

Posted: 11:45pm 16 Jun 2010

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How about one of these with a change over relay. When your batteries are charged switch the panels over to the inverter. It sounds as if the inverter needs the internal resistance of the panels to limit its input current.

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 12:22am 17 Jun 2010

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Hi Robb

Could go that way the only thing that concerns me is that if you are using 24 volt nominal system the voltage of the lightly loaded panels could go to high, as mine when unloaded can exceed 40 volts on a good day, whereas the battery float voltage is 27.2.

On a 12 volt system voltage is OK but amps may still exceed the maximum {20 amps?}
On the panels Marcus has at the moment this isn't a problem but if upgraded to larger panels in the future it may be. At present around the 10 amps max mark no problem.

All the best

BobEdited by VK4AYQ 2010-06-18

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MacGyver

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Joined: 12/05/2009
Location: United States
Posts: 1329

Posted: 01:55am 17 Jun 2010

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Marcus20VT

Have you thought about calling the manufacturer on your private home or cell phone first? I think I'd get their opinion before I started experimenting. I'm a registered, card-carrying techno-dummy, so that'd be where I'd start.

Just an observation.

. . . . . Mac

Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 07:28am 17 Jun 2010

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Hi Marcus

I sent a email to the agent regarding the inverters as I am looking at getting a 1200 watt one I enclose his reply.

Dear Bob
?
For several solar panel or grid tie inverter you can connect as the attached photo.
?
When the solar panel current is more than the rated input for the inverter,then the grid tie inverter just can transfer 1200w into mains supply,thanks
?
Regards
?
The photo was the one on ebay

I would take this as current limiting so I have sent him a email to clarify the 300 watt unit as well I will keep you posted when I get a reply.

All the best

Bob

Foolin Around

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 07:39am 17 Jun 2010

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Hi Marcus

I have one on batteries 24 volt system and a 12 amp fuse and the smoke has stayed in so far but not sure if it is the same as yours as it was sold to me as a solar and wind suitable unit, I use the dump load switcher to switch it on when the batteries go above 27 volts and switch off again at 26 volts that regulates the battery voltage so it doesn't get to high, in the winter it doesn't come on much but in the summer it is on most times.

All the best

Bob

Foolin Around

Marcus20VT
Regular Member

Joined: 02/09/2008
Location: Wales
Posts: 49

Posted: 04:09pm 17 Jun 2010

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Wow - thanks for all the replies and the effort guys - fair play!!
Bob - thanks for that - Please let me know what he says abourt the 300W one. Although I must admit i don't really understand his reply!
I'm trying to achieve the simplist most economical way for this to work - (cos basically I'm lazy and tight!) - so I will probably be connecting a couple of sla's to make a 24v battery which will limit the voltage to the gti and then put in a 10A inline fuse and pray for zero smokeage!
Mac - pmsl - yes you are soooo right

Honestly, he is never in when I get home from work and I'm the worlds worst at messages. I've got a day off tomorrow, so will try to clarirfy a few things.
Thanks to you all again for your help

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 12:08am 18 Jun 2010

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Hi Marcus

I got a reply on the 300 watt but it is in Chinese English so it could mean anything, the best way is to go for the 10 amp fuse and suck it and see, as I wouldn't depend on his reply. The best way is to put a current limiter in series with the unit and be on the safe side.

http://www.alt-nrg.org/pwm-v2.html

This is a limiter I use with success but it needs more heat sink on the FET than shown in the construction.

All the best

Bob

Foolin Around

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 03:18am 18 Jun 2010

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I am not supprised they wont take your calls as the problem is spelt out in the name "Onenation" and if they do answer, you will more than likely get greeted with ......Please Explain......

Pete.

Sometimes it just works

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 02:08pm 18 Jun 2010

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Hi Marcus

I did a little more research on the 300 watt unit this evening and it seems that it has a MPPT on the input side to optimize voltage but no mention on current limiting, but reading between the lines they say it is suitable for a 300 watt wind turbine, and as a 300 watt nominal turbine can produce 5-600 watts in a strong blow it makes me think it has some sort of limiter on it, Trying to get any tech information out of them is like trying to pull a tooth from a toothless man, they just parrot what they have been told by someone else that doesn't know either.

So back to the fuse or current limiter then play with loadings from there.

I read the info sheet that came with mine and it said in the small print it was a 300 / 600 unit depending on input voltage and that seems to be correct for it as when I checked it drew 20 amps from memory on 24volt battery I haven't tried it on 12 volts.

Have fun

All the best

Bob

Foolin Around

Marcus20VT
Regular Member

Joined: 02/09/2008
Location: Wales
Posts: 49

Posted: 06:03pm 24 Jun 2010

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I finally got through to them on the phone - mmm that was an interesting conversation

"Hello"
"oh Hi, is that one nation renewables"
"Yes"
"err OK, can you put me through to technical support"
"not available"
"ok, then can I speak to someone in customer service please?"
"maybe I can help you"
(Probably not methinks, but lets give it a go anyway) - "OK, I recently bought a 300watt grid tie inverter from you. I was planning on using it from DC batteries charged by my solar panels but upon reading your accompanying literature, it states I am not meant to do this. Can you tell me why please, and if it is a case of limiting the current, can I do this via a fuse or would I need to install an active current limiting circuit between the panels and the grid tie inverter?"
"I will take your name and someone will call you back"
I give her my name
"OK, someone will call you back shortly. Bye"
"err, do you want my number? Hello? Hello?"
Hangs up and phones back giving my number.

Suffice to say I haven't had a call back, so it looks like we,re on our own boys!!

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 09:26am 25 Jun 2010

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Hi Marcus

I got them to send me a repair manual for the 300 watt unit and it had four pages on how to change the fuse.
About as much good as a hip pocket in a tee shirt

All the best

Bob

Foolin Around

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