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What Charge Controller and can I add it now


djacobs
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Hi All, I need your advise as a beginner. I have 12 x 250W Panels connected in 3 x 4. 12 x 105 Ah Dixon Batteries (3 x banks in serial/parallel) , 1 x 48V Axpert 5KVA (4000W) inverter. I do not have a charge controller and was advised that I need one. What size do i need for my setup and how do Iconnect it to my current system. The solar shops are talking about 40A/50A - 48V required. These days I dont trust anyone after my bad installation, that I am trying to fix.

Please assist

Daniel

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17 minutes ago, djacobs said:

105 Ah Dixon Batteries

Which model Dixon batteries do you have?

I ask for the 105ah are not really deep cycle. Better than most, yes, so you have to be careful.

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Doesn't the Axpert have a built-in charge controller?

If you want to add an external one, then due to the way the MPPT works (buck converter) you can pretty much take the peak power of the PV modules and divide it by 48.

12 * 250 = 3kwp, 3000/48 is going to be slightly more than 60A (50 * 60 = 3000). Because you rarely get the peak, 60A will do.

I can tell you what not to buy. Don't buy the WRND controller.

The two controllers I know and recommend are either the Victron 150/70 (70 ampere) or the Microcare 60A unit.

In practice you will be better off with two smaller controllers, eg Victron 150/35.

There is no cheap way to do it, it's going to set you back at least 10k :-/

Batteries are around 300Ah, so recommended charge rate is between 30A and 45A. 60A is 20%, pushing it a bit but okay :-)

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I don't know the Axpert well enough to tell you where, but I can explain the charge rate. If you have a 100Ah battery, you want to charge it at a rate that's about 5% to 15% of that, so 5A to15A for each 100Ah string.

You have 12 batteries arranged in 3 strings of 4 each. Each string has the capacity of the individual batteries (105Ah) and the three strings in parallel multiplies that by 3 (roughly 300Ah to make the math easy). This means 15A to 45A. BUT... you can go slightly above that without danger, your efficiency just suffers somewhat, so 60A is okay, especially since it will only reach that for a short time in the middle of the day, and you're also consuming some of the power at the same time.

Personally I would be a little uncomfortable with such a setup. With three strings, I'd want them to be individually fused. If one fuse blows, you now have 60A on a 200Ah bank. So it might be better to limit it to 50A and sacrifice a bit of power in the middle of the day (ie, you have an oversized array configuration then).

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Hi @djacobs

To start of you would need give us the batteries speck sheet so that the "correct" settings for the Axpert can be given. I assume that you have not connected the setup yet? Considering that this will most likely be a long term investment I would also advise that you read through the Axpert manual and familiarize yourself with the settings within its menu as you will then also have a couple more questions :).

If you don't already have one you should also consider to get a BMV battery monitor as the Axpert is not really accurate with its battery charge levels. Last time I checked the forum store had them for n decent price else you can also chat to @Camel.

 

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The batteries are the Dixon DC105DT.

They are very good batteries for starting to learn about batteries.

2 reasons:
One: Because you can add water to them.
Two: They have good cycles compared to most other "deep cycle" UPS batteries:
At 50% DOD = 800 Cycles
At 20% = +-1040 cycles.

So keep them at 20% DOD or less and see how long you can keep them in play. Once they have to be replaced, you will know a lot about batteries and their care, and about your needs.

Dixon - DC 105 DT Data Sheet.pdf

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2 minutes ago, djacobs said:

How do I set the DOD on the axpert controller.

You need a BMV as per Paul.

Without the BMV, you are pretty much going to drain the batteries quite soon for the Axpert's SOC is based on volts. And that does not work well.

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The BMV shows how much of your batteries capacity you have used. So basicly it is a management tool. There is guys that has used the bmv to "switch" over to mains once a certain level in state of charge (SOC) reached but for now I would say first get to know what your system does and what your consumption is and then go on to the next level. 

How do you currently charge your batteries?

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12 hours ago, djacobs said:

I have 12 x 250W Panels connected in 3 x 4. 12 x 105 Ah Dixon Batteries (3 x banks in serial/parallel) , 1 x 48V Axpert 5KVA (4000W) inverter. I do not have a charge controller and was advised that I need one.

 

11 hours ago, plonkster said:

Batteries are around 300Ah, so recommended charge rate is between 30A and 45A. 60A is 20%, pushing it a bit but okay :-)

What, who gave you that advise? The Axpert already has a built-in charge controller, why would you need a separate one. You might score a little in efficiency if you add a very good external charge controller, but the price and effort will certainly not justify it. As mentioned above, you should charge the batteries at about 10% of the Ah rating, that is 10% of (3 x 105) => 31.5A, but as @plonkster mentioned, you can charge at a bit more than that, up to about 14-15% of the Ah, so I would not recommend that you set the Axpert to a charging current of 40A.  And add fuses to the individual battery strings as well.

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1 hour ago, djacobs said:

I think this has already happened.

You can do two things - if batteries are fully charged:
Check the gravity level of each cell the batteries once they are fully charged.
Take the batteries to Dixon or a motor electrician shop for a load test.

You may have one or two batteries problematic, but you need to replace the whole set.

Sell the ones that are still ok. I may want some. Then ones that are dead, sell them for their lead weight. 

Then look at Trojan T105RE's.
 

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49 minutes ago, djacobs said:

Thanks, at what setting

Maybe you should check all your settings, not only the charging current. The Axpert has a maximum charging current setting (setting 02), which in your case should be set to 40A for the current bank and then it also has a maximum utility (grid) charging current (setting 11) which you have to configure depending on if you want to charge your bank from the grid and at what rate, say in case the batteries are discharged below a certain level at night or during a cloudy/rainy day - that setting is entirely up to you, but again should be set to a maximum of 40A.

You should also check all of the following settings: 01, 05, 12, 13, 16, 23, 26, 27, 29 & 31 - a lot of these are determined by the battery type and specific -properties.

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Something interesting is since I changed the panels on saturday after two years, to 4 x 3 my voltage has gone up and the batteries started bubbling, contacted Dixon and says that the battiers are actually now charging. Sett setting 2-40A, dont know what to change next.

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At least it "sounds" promising.

IMO I would say , start by getting your current values from the inverter and post it here then should be able to tell you what setting should be changed , if necessary .  What I did , in the beginning , was to take a picture of every setting and save the info to a spreadsheet there after so that it is alway at hand. 

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OK, the Dixons want a 59.2V bulk charging voltage, although the Axpert can only go up to 58.4V. The float charge setting of 52.8V is correct. Everything else looks fine.

Setting 11 is set to 2A, which means that the batteries will be charged at 2A if PV is insufficient e.g. on cloudy / rainy days or during nighttime, if needed. If you are OK with that, you can leave all the rest as-is.

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