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Axpert 5Kva Current Measurement


edmundp
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Hi All,

 

How is everyone experiencing the accuracy of current measurements done on the DC side of this inverter?

 

I have one and a BMV 700 and I am finding a constant 1.5 to 2.5A discrepancy between what the inverter says and what my BMV says - both in the wrong way. I.e. when charging the inverter will report a higher current than the BMW and when drawing the inverter will report lower than the BMV. I have checked and set the BMV to a zero current with everything off.

 

Any way to fix this as it has a bit of an implication to battery charge cycles and when my batteries are placed under float.

 

I had this under both the old and new firmware for inverter and MPPT. Made no difference. New firmware seems to be stable though. No issues thus far.

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On a 24V bank 2% is fine.  Let us look at the theory. If one cell in a battery bank is high/low by 0.5v then in a 24V system that would account for roughly a 2%  difference. In a 48V system it would account for only a 1% difference. The seriousness would be the same but the imbalance would go undetected in a 48V system if your mid-point threshold is set at 2%.

 

I have just received 3 Lithuanian (Chinese) battery balancers and fitted them this afternoon. I was hoping to have a look inside but they are sealed. I am hoping to see an improvement in my bank since they can transfer up to 5A between batteries and my old double Zeners could only bled off about 1A. 

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Chris, this topic has been bothering me for a while now.  :D

 

I have 4 x 6v 225ah batteries in 24v configuration. 

a) Would you add a balancers to them?

B) Where can I find them?

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I have just imported 3 of these 

http://www.ebay.com/itm/221839283113?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

You could build 4 Zener regulators for 6V.  http://www.evdl.org/pages/hartregs.html

 

I am a beginner electronics DIY and I am toying with an idea to identify your two batteries most out of balance and connect them with relays and bring the voltage on one up the other down and do the same with the remaining two batteries. After a set period test to see if the batteries ranking according to voltage has changed and redo the exercise. One would need several  voltage comparators  and a micro-controller but I am not sure whether I want to go with a Op-Amp or not. The trouble I see is that the correcting flow may not be very high. With my big 260 Ah batteries they are still going out of balance late absorb as the current in from the charger is more than the current out due to the balancers. I had thought of balancers and Zeners but the nest of wires that would be the result is too much for me.

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Thank you. Keep us posted on how well they work?

I have also asked my battery supplier on what they have to add, way I see it, if they can do the work for the batteries they sell, it will make my life easier.  ;)

 

My next question.

Batteries are being charged whilst inverter is operating, as is with most solar only installations, meaning current in and out all the time.

 

I presume this has a rather huge impact on balancing?

I go further and presume one can only really do this properly when you equalize the batteries every few weeks, i.e. inverter is off at the time.

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What has the biggest impact on balancing is appliances that have a intermittent heavy draw (iron etc). The charger is limited to 20A  (due to not exceed C10 charging rate for 260 ah batteries) and you find the charge current at about 12-14A and then the iron thermostat reaches temp and then the charger takes a few seconds to compensate for no draw and 2 min later there is a draw again. Have just noticed the BBs working measured the current using a  DC clamp ammeter  50 mA for about 1 min  so they work.

 

Just measured 250 mA so the Chinese balancer is having a effect. The problem is that for instance if battery 4 is high and battery 2 low current first has to flow through 3 to balance out 4 and 2. With relays you should be able to transfer energy from highest to lowest voltage batteries.

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Asked them if they can handle 6v Torjan batteries. Yes they can.

 

Hello Jaco

 

yes it will but Please contact our reseller - current automation.

thanks

 

Dr. Ian de Vries

Mobile: +27 82 717 8389

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Hi has anyone had any luck in getting these inverters to run in 'Economy' mode at night, seem this feature is disabled in some modes.  I would love to see a very low drain in the dead of night I've even moved most of my small loads to Eskom.  I'm experimenting using a 25A contractor (Relay) to switch my AAA fridge over to Eskom at night so I can get below 50w on the inverter to go into economy mode.   It breaks my heart to see all my daytime savings trickle away from my batteries overnight (like 3Kw/h in total). 

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3kwh over night!? Good grief that's like .... 3000/8, lets say 3200/8 to make the math easier, 400W quiescent? Which at 48V is like 8 ampere... Seriaas?

 

If it was me, before I did anything, I'd measure the quiescent current using an amp-meter. Should be able to do it with any digital multimeter with a 10A range, though just be sure the inverter has no loads, and perhaps put a 10A fuse in line just in case. Or ideally, a clamp meter that can do DC (ie hall effect), though these things are expensive enough that most people probably don't own one.

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I don't actually know how much my Multiplus uses, but it is not enough to notice. I also have to check my charge controller :-)

 

I checked the previous charge controller (The Microcare) and that one needs around 60mA when it sleeps, so that's about 1.5W. About half of that is the backlight of the LCD, so they could significantly reduce it by turning the LCD off at night. While I'm repairing it (I messed up with a part number and waiting for the new one) I might look into that :-)

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   It breaks my heart to see all my daytime savings trickle away from my batteries overnight (like 3Kw/h in total). 

It would break mine to.

 

My Axpert uses between 30 and 40W when I have the grid connected and it is in bypass mode and I am not charging the batteries. Kurt one of the forumites on the Aussie site measured his quiescent current at 46W. To me 3kW/h seems excessive. 300 - 500 W overnight would be more acceptable. How are you determining a draw of 3kW?

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If wonder what total amps are drawn if you use a separate charge controller, inverter and say other monitoring equipment at night on standby?

 

The more features they have, the more power they will use, but I still wonder how that will compare to the Axpert/RCT/Mecer units.

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I haven't yet measured the new Blue Solar 150/70, but my old Microcare MPPT controller uses around 60mA in standby, estimated, because I had to guess how much the DC/DC bit requires (it needs 5mA while sleeping, but that's on the other side of a 2:1 isolated boost converter that probably operates at around 80% efficiency, so more likely 12mA on the input side, plus a measured 45mA for the rest). At 24V, that's 1.5 watt. The Microcare keeps its backlight on all the time and there is no provision for dimming, so more than half of that is likely for the LCD backlight. I only have this data point so far... at some point I'll probably get a chance to measure some of the other stuff :-)

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Did some Googling.

Victron 1600VA Phoenix:Zero-load power in AES mode 8w (but the 5000va one draws 20w)

Plain old Tristar 45 Controller: <20mA

BMV700: Current draw, back light off < 4 mA

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Just to clarify the 3Kw/h is 400w per hr over 8 hers (3.2kw) this is my total night load, including a AA fridge, alarm, e fence and a few LED security lights. 

I've measured this with an Efegy and the Prepay & Fluke meter (drain ave over 8hrs) 

I guess I'll put the fridge back on the grid at night and shut the inverter down when igoto sleep ?

Any other suggestions ?

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