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Lets test what the LiFePO4 noise is about...


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So I took the plunge to what these Lithium batteries can do.  3.6kWh installed and made it work very hard - pulled 100 Amps out of it for 5 minutes to check heat and it did not flinch.  Interesting... will keep you posted. 

 

PS I was so eager to fire it all up that I only noticed the two wires between the MPPT and PV combiner box still needed tidying up later...

O and then there is the tale of the blown MPPT because the battery's protection kicked in due to an incorrect setting on the inverter but hey, every now and then when we get to confident I guess we need a bit of smoke to keep us humble.

20160521_133553.jpg

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Yes I did.  I sent it back already to be fixed but looking from the right of the unit where I was standing I could see arcing through the vent slots.  The battery has a 58V cutout protection (against over charging).  The MPPT was set to not go that high but when I switched on the Eskom power to the inverter, the inverter started charging at 58.4V, the battery cut out and there was about 1.3kW PV being generated at that instant.  

Sounds like the problem is that the MPPT really does not like being disconnected from the battery with PV coming it.  It does say that you should never do that in their manual but it is strange that there is no internal protection against that (like a latching relay that only closes if battery power is present).  

The fact that the inverter was charging at that point and then all of a sudden the path to the battery was broken, it begs the question what happened to residual charge in the caps and other bits on the inverter side.  That could also have caused the smoke in the MPPT.  Now the fact that the inverter charged at all is just my own stupidity.  I should have checked the settings before I gave it Eskom power.

I am chatting to Microcare about all this to see what can be done.  These new batteries are awesome but clearly there are new things to be carefull of and a bit of a learning curve on setting up charging patterns and the like.

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15 minutes ago, Hannes7212 said:

Sounds like the problem is that the MPPT really does not like being disconnected from the battery with PV coming it.  It does say that you should never do that in their manual but it is strange that there is no internal protection against that (like a latching relay that only closes if battery power is present).  

When I looked at my 40A unit, there does seem to be some kind of protection built in. There is an extra MOSFET in the positive line that appears to be wired as some kind of protective device that can cut off the  PV side, but I suspect its job is to ensure that no back-feeding happens at night. Still not quite sure... it wasn't completely clear, and I for what I was doing at the time I didn't have to know what that bit does... :-)

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My guess would be that you probably blew the SMPS. It has a Switch Mode Power supply that brings the voltage down to 12V, and those things are usually rated at 70V input or so.

From the 12V rail it runs the fan, and it also runs a step-up converter that generates an isolated 15V supply for switching the MOSFET on the high side. Then it uses a 7805 linear regulator to step the 12V down to 5V for the rest of the circuitry.

Attached image of the control board. SMPS is in the red block, 7805 in the blue block, transistor that switches on the fan in the yellow block, the green part is the step-up converter for driving the mosfet.

mc.jpg

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  • 2 weeks later...
On 2016/06/03 at 7:28 PM, Weasel said:

Those look like AC rated breakers.

Yup, its AC breakers, but it's nice and beefy. I don't think there is necessarily something wrong with that. Every AC-capable breaker can be used for DC... just at a much lower rating than the AC rating. It can generally handle the same current (RMS!), just at a much lower voltage (because it has to be able to extinguish the arc). I would like to think that Microcare did their homework when they put these in.

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3 hours ago, plonkster said:

Every AC-capable breaker can be used for DC... just at a much lower rating than the AC rating.

Sure this is true, its mechanical contact after all but there are rules involved and it does look like a 60A mppt? and i'm guessing 63A AC rated breaker. Breaking the arc will be harder with DC so yes the voltage will have to be lower but now Its the safe current handling that's the issue here. As voltage lowers contact resistance becomes more of an issue. That's why you will see some dual rated breakers having  63A AC and as low as 7A DC, because the DC rating was given at say 40V.  its probably a discussion for a another thread entirely.

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It's a 40amp unit. The breaker is 63amp 600v if I recall. Worst it will ever see is 120 volt at 20 amps PV side, or 60 volt 40 amp battery side. I've questioned this myself, but it's how it comes from the factory. :-)

You tickled my interest now. Looking at it more closely, it is rated IEC-60947-2, which if my google-fu is up to date, is an industrial-spec breaker (not the lesser residential type). I_n is 50 amps, and if the usual rule-of-thumb derating I remember from school is applied, it should be good for up to 60V at that current (it should not arc over). It's job in this application isn't protection, it's isolation. If there is a bad short inside this unit and you have the whole battery current going through there... it will be bad. Use it with a suitable fuse and you should be fine. I'm no expert of course, but that's how I understand it.

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Well since it is a current limited device the worst it will ever see with respect to the power dissipated in the breaker is 44V 40A and it would see that for a while when flatteries are charging. but its like you said 

13 hours ago, plonkster said:

I would like to think that Microcare did their homework when they put these in

 

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  • 7 months later...

Hi there, I am very impressed having tested them for almost a year now and having gained lots of experience with client installations using these batteries.  The main advantages that are obvious are:

- Charge / discharge rate hardly affects capacity

- The efficiency is clearly visible.  I estimate a 15 - 20% overall improvement in my old lead based system.  

I am using the MyPower24 batteries because I struck up a great relationship with the company and their technical expertise is top notch.  I am attaching a photo of my not so neat test environment (please look at my business page if you want to see neat installations - which I cannot advertise here but send me a message and I will direct you).  I am moving into a new home in a month then I will rig the whole place off grid (with grid backup for bad weather) with these batteries.  Dimensions are 600 x 400 x 200 deep.

Cheers! 

20170105_154643.jpg

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