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Battery Charge Rates


Chris Hobson
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As I spend more time researching solar so I realise that I need to know a whole lot more.

 

The 260 Ah batteries are rated to take a maximum charge of 78A and I presume that would be true for 4 batteries connected in series. 

 

Literature on the web recommends not exceeding a charging current of 10% of the Ah rating (26A) or C/8 which is a bit less (21A). 

 

The Axpert can charge up to 60A DC and 60A AC

 

.So does one limit one's self to 25A DC?  The minimum max charging current is 70 A for the Axpert.  ( obviously designed for a battery bank much larger than what I have purchased.

 

And what would the conversion to DC be for say a 10A AC charging current?

 

Chris

 

 

 

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Hi Chris

 

I assume you are referring to what they call "Joint Utility and Solar Charging" current (page 30) when you mention 60A DC and 60A AC?  That will not be an AC input current of 60A, but rather 60A DC from the Utility (60A DC output from the built-in AC charger) and 60A DC from Solar and that is why they have the value of 120A Max.

 

If you were drawing 60A AC (@ say 220V), the current at 50V (48V) will be ((220 x 60) / 50) => 264Amp - Please note that this is just a sample calculation for illustrative purposes.

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The generator goes on in the evening for my employees and myself. When the generator goes off at 9 to 9:30 pm I would like to have a fully charged set of batteries to carry demand 1 solar compatible fridge and 1 solar compatible deep freeze. I hope by not exceeding DOD of 30% that the batteries will not take high currents. The are rated for 78A but would prefer to be closer to 25A. I will just have to see once we up and running how the system behaves. The Axpert has a minimum of 200Ah so I know I am just within the acceptable range. My feeling was I live is a really sunny environment and probably do not need the autonomy that one would need where the is a bit more cloud cover. The fact that we have a generator running anyway (until my staff are also on solar) means that evening (a critical time since there is no PV production and usually a large draw) needs not to be catered for. I am unlikely to get another 4 batteries in a hurry.

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The generator goes on in the evening for my employees and myself. When the generator goes off at 9 to 9:30 pm I would like to have a fully charged set of batteries to carry demand 1 solar compatible fridge and 1 solar compatible deep freeze. I hope by not exceeding DOD of 30% that the batteries will not take high currents. The are rated for 78A but would prefer to be closer to 25A. I will just have to see once we up and running how the system behaves. The Axpert has a minimum of 200Ah so I know I am just within the acceptable range. My feeling was I live is a really sunny environment and probably do not need the autonomy that one would need where the is a bit more cloud cover. The fact that we have a generator running anyway (until my staff are also on solar) means that evening (a critical time since there is no PV production and usually a large draw) needs not to be catered for. I am unlikely to get another 4 batteries in a hurry.

Have you tried the generator on the Axpert yet?

 

My Axpert doesn't seem to like it much, keeps beeping a lot, though I can't see what the error / reason is. It's only a 6900VA generator thought so I don't know the generator doesn't produce clean-enough power.  

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Hi Silver

What sort of Generator is it? The single cylinder petrol standby plants are good but battle to maintain 50 Hz. As you draw increases there is a drop in revs and the governor increases fuel flow and revs respond  but there is some variation. The bigger diesel generators run much more evenly. I am waiting for a DC isolator switch before connecting my panels and so will continue with the AC wiring tomorrow and the battery cabinet. I sure hope that there is not a compatibility problem between generator and inverter. Have you tried setting your  max utility charge to 10A. giving the generator less work to do. The manual reckons that the input voltage could be between 170-280 AC UPS mode and 90-280V for Appliance mode so the Axpert should have a wide tolerance. Maybe I am misunderstanding the manual (won't be the first time). 

 

Chris

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Hi Silver

What sort of Generator is it? The single cylinder petrol standby plants are good but battle to maintain 50 Hz. As you draw increases there is a drop in revs and the governor increases fuel flow and revs respond  but there is some variation. The bigger diesel generators run much more evenly. I am waiting for a DC isolator switch before connecting my panels and so will continue with the AC wiring tomorrow and the battery cabinet. I sure hope that there is not a compatibility problem between generator and inverter. Have you tried setting your  max utility charge to 10A. giving the generator less work to do. The manual reckons that the input voltage could be between 170-280 AC UPS mode and 90-280V for Appliance mode so the Axpert should have a wide tolerance. Maybe I am misunderstanding the manual (won't be the first time). 

 

Chris

Hi Chris, 

 

It's a Ryobi 6900VA generator. I'll try the 10A charge setting and see if it works 

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 My experince of generator charging is don't charge at too high a current. I can set the maximum charging current on my inverter/charger and initially I had it too high and the battery voltage would go up quickly, then the charger thought they were charged and then stopped charging until the battery voltage dropped down again. So it would go through this loop about every 5 mins.. So that was not very effective. I had set the charger at 15A at 220V so more like 60A at 50V for charging. (this was 4x150Ah batteries in series). If I reduced the charging current to 5A @ 220V, so about 20A @ 50V than the batteries charged nicely. I now have 8x150Ah batteries and set the maximum charge at 10A @220V, so about 40A on the batteries. I couldn't find any mention of maximum or optimum charging current for my batteries so that is just my experience.   

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Thanks DeepBass9. I have always tended to charge batteries at a lower current but I have never invested so much money in batteries. Apparently one must not charge at too low a charge rate with flooded batteries otherwise you stratify the electrolite.  

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  • 3 weeks later...

Hi Chris, 

 

It's a Ryobi 6900VA generator. I'll try the 10A charge setting and see if it works

Ok, so that doesn't work. I set the utility charge to 10A (Axpert menu option 11) but the generator it still doesn't see the generator's input. The red light doesn't flash but I can hear the Axpert beeping.

Can anyone else with a similar generator see if it works on their end?

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Ok, so that doesn't work. I set the utility charge to 10A (Axpert menu option 11) but the generator it still doesn't see the generator's input. The red light doesn't flash but I can hear the Axpert beeping.

Can anyone else with a similar generator see if it works on their end?

Hi Silver

 

When I first connected my Axpert my panels were not connected. The Axpert beeped and moaned. I then set program 3 back to the default Appliance rather than UPS. Since then the  inverter has behaved flawlessly. In Appliance mode there is a noticeable flicker but my computer does not reboot.

 

 I have recently installed a Victron battery monitor and am now much more confident in SOC etc. The PV charging is faultless but the AC (generator) charging may be causing the battery bank to be out of balance. I am not sure yet I have only noticed it recently and have not had chance to observe enough cycles. 

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Hi Silver

 

When I first connected my Axpert my panels were not connected. The Axpert beeped and moaned. I then set program 3 back to the default Appliance rather than UPS. Since then the  inverter has behaved flawlessly. In Appliance mode there is a noticeable flicker but my computer does not reboot.

 

 I have recently installed a Victron battery monitor and am now much more confident in SOC etc. The PV charging is faultless but the AC (generator) charging may be causing the battery bank to be out of balance. I am not sure yet I have only noticed it recently and have not had chance to observe enough cycles. 

Thanx Chris, 

 

I tried both the APL and UPS mode but in neither case does the generator allow it to charge the batteries. The "AC" icon flashes, as well as the green light. So I'm not sure what I need todo, or install in order to allow the generator to charge the batteries. 

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Thanx Chris, 

 

I tried both the APL and UPS mode but in neither case does the generator allow it to charge the batteries. The "AC" icon flashes, as well as the green light. So I'm not sure what I need todo, or install in order to allow the generator to charge the batteries. 

I presume by the "AC" icon you are talking  about the circle with the sine wave through it, and that the green light flashing is the left most LED. The green light flashing indicates that your inverter is working and current is being supplied by the inverter either from PVs or the batteries. Can you supply grid power to the inverter? If so does Eskom/grid charge your batteries and you are only having trouble with a generator charging your batteries? You may or may not have noticed a small button on the left bottom of the inverter and this is a circuit breaker. It does not say what its rating is but it may have tripped.

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Hi Silver 

 

Found this this evening - unfortunately not good news!

Aussie chap reckons the Axpert does not like portable gennies. I am fortunate that my gennie does power my inverter. It would have been a disaster as I designed my whole system with gennie power meeting part of the demand.

 

Chris

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I presume by the "AC" icon you are talking  about the circle with the sine wave through it, and that the green light flashing is the left most LED. The green light flashing indicates that your inverter is working and current is being supplied by the inverter either from PVs or the batteries. Can you supply grid power to the inverter? If so does Eskom/grid charge your batteries and you are only having trouble with a generator charging your batteries? You may or may not have noticed a small button on the left bottom of the inverter and this is a circuit breaker. It does not say what its rating is but it may have tripped.

Yes, when I say "AC icon", I mean the circle with the sine wave through it ;)

 

When Eskom is connected the Axpert charges the batteries fine, but as soon as I switch over to a generator, it doesn't charge. 

I did notice the circuit breaker, which didn't trip. It has a 40A rating. 

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Since Eskom is charging there is nothing wrong with your setup. My only conclusion is that the small generator supply is not good enough for the Axpert. I have a small generator that I was going to wire as a backup to our main generator. I sent it to town because it was hunting. I will test it against the Axpert when I get it back before I permanently wired for the Axpert and then find it does not work..

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Hi Silver 

 

Found this this evening - unfortunately not good news!

Aussie chap reckons the Axpert does not like portable gennies. I am fortunate that my gennie does power my inverter. It would have been a disaster as I designed my whole system with gennie power meeting part of the demand.

 

Chris

I only got time to watch the video now, and it confirmed what I'm seeing on my side, though he didn't mention much about the phenomena. 

 

The question is, why? Why does this happen, or what is causing it, or how do I fix it?

 

And, Chris, what genie do you have, that works fine with the Axpert?

 

I want to use an Axpert on the farm where there is no Eskom, and have the genie as backup. 

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Hi Silver

 

I initially thought that  why one gennie works and not the other might have something to the frequency. I set our gennie to 50Hz using a old analog frequency meter (it has little metal rectangles that vibrate and you adjust the revs until you have the right frequency). Now that I have an Axpert I see my frequency that I thought was stable is all over the place. The Efergy monitor reckons that it is 50 Hz so maybe the Axpert reading is rubbish.

 

It appears for a little research that the reason that inverters do not like generators is that they often do not produce a pure sine wave. You are going to have to look at a line conditioner or perhaps cheat and convert your AC to DC and fool the inverter that it is solar power. Perhaps you can create a hook-up at you  solar combiner box. I don't know whether you get a DC transfer switch. I may be worth your while to hook up an oscilloscope to see what you gennie is producing. 

 

I have a 3 cylinder LIster driving a 3 phase 10 kVA Compton-Greaves alternator. 

 

Outback have done some tests and the only generator they found to have good enough power was the Honda EU series.

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You are going to have to look at a line conditioner or perhaps cheat and convert your AC to DC and fool the inverter that it is solar power. Perhaps you can create a hook-up at you  solar combiner box. I don't know whether you get a DC transfer switch. I may be worth your while to hook up an oscilloscope to see what you gennie is producing. 

 

That is a great idea! Just remember that if you rectify the AC you will have a much higher DC voltage 250VAC x 1.414  => 354VDC - can your inverter accept "solar" at that voltage? The Axpert 5KVA can only go up to 145VDC.

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