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2-3kw battery charger for charging 48v batteries with 5kw generator


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Hi All,

Can anyone offer advice on a cost effective battery charger for connecting my old generator to my 48v lithium batteries?

For use as a last resort when Eskom and/or the municipality fail for an extended period AND the big fire ball in the sky is hiding behind bad weather.

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It depends if your Inverter is compatible with generators. Most Axpert inverters are sensitive to generator input. In my case I use an ON Line UPS with double conversion and output of pure sine wave AC. The generator must be at least twice the size of your inverter(in Watts) and UPS more or less the same size as your inverter. But you mentioned a battery charger. What type of battery charger?

Just my 2 cents.

 

Edited by IcePick1957
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48 minutes ago, IcePick1957 said:

It depends if your Inverter is compatible with generators. Most Axpert inverters are sensitive to generator input. In my case I use an ON Line UPS with double conversion and output of pure sine wave AC. The generator must be at least twice the size of your inverter(in Watts) and UPS more or less the same size as your inverter. But you mentioned a battery charger. What type of battery charger?

Just my 2 cents.

 

Ironically my inverters (Sunsynk) can support a genset when stand alone, but once paralleled present some problems. Their recommendation is to buy another invert (smaller in my case) to run as an independent charger. but dropping R20k+ for a 'charger' that will have perhaps a 1% annual duty cycle makes little sense

I'm not an expert on what type of chargers are available, but I'm looking to charge 4 off BSL 6.4kWh batteries.

To my mind, the advantage of having an independent charger is that load stays at say 3kw which is more optimal for the generator rather than the genset ramping up and down with house load with the associated frequency issues a small generator has with change of load. The batteries then act as a buffer and the inverters on the 'other side' of the batteries deal with load fluctuations as normal.

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No on else that can offer some insights?

Alternately, are there any 3kw low cost inverters that are generator friendly that could be re-tasked to this purpose? Or even an inverter where something has failed e.g. the MPPT has failed but the battery charging facility still works?

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  • 1 month later...
On 2022/03/31 at 3:34 PM, Greatwhite said:

No on else that can offer some insights?

Alternately, are there any 3kw low cost inverters that are generator friendly that could be re-tasked to this purpose? Or even an inverter where something has failed e.g. the MPPT has failed but the battery charging facility still works?

Have you found a solution yet? What about a manual change over switch between grid and inverter where you can substitute the grid supply with generator supply? You might have to do some load shifting while charging batteries combined with base load. 

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On 2022/03/29 at 8:44 PM, Greatwhite said:

Ironically my inverters (Sunsynk) can support a genset when stand alone, but once paralleled present some problems

How many inverters do you have in parallel, and what is the minimum load you can run?

Maybe if loads are low enough, switch off all except one inverter, and connect the generator to that one only. Should work.🤔

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  • 1 month later...
On 2022/05/05 at 4:44 PM, Vaal said:

Have you found a solution yet? What about a manual change over switch between grid and inverter where you can substitute the grid supply with generator supply? You might have to do some load shifting while charging batteries combined with base load. 

I found some stuff from China that is a nominal 48v battery charger designed for charging LiFePo batteries which I am mulling over - about R3k. It even has CANBUS which would be great if it could be integrated to the CANBUS on the inverters & batteries, but according to a mate of mine that deals with CAN, it can be a minefield, so am contemplating just using the ATS trigger on the inverted to simply switch on/off the unit at the lower and upper thresholds.

Manual change over between grid and generator will still present a problem, I think, since since the generators ability to reliably maintain 50Hz with load fluctuations will still exist. 

 

On 2022/05/05 at 6:35 PM, TimCam said:

How many inverters do you have in parallel, and what is the minimum load you can run?

Maybe if loads are low enough, switch off all except one inverter, and connect the generator to that one only. Should work.🤔

Two x 8kW inverters in parallel. I believe you are probably correct and something I considered, but:

1. I'm not sure this is something I could ask the wife or kids to do if I'm not there.

2. The smallish (+/-4.5kW actual) power of the genset, still presents the 50Hz synchronization issue as loads fluctuate.

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1 hour ago, Greatwhite said:

I found some stuff from China that is a nominal 48v battery charger designed for charging LiFePo batteries which I am mulling over - about R3k. It even has CANBUS which would be great if it could be integrated to the CANBUS on the inverters & batteries, but according to a mate of mine that deals with CAN, it can be a minefield, so am contemplating just using the ATS trigger on the inverted to simply switch on/off the unit at the lower and upper thresholds.

Manual change over between grid and generator will still present a problem, I think, since since the generators ability to reliably maintain 50Hz with load fluctuations will still exist. 

 

Two x 8kW inverters in parallel. I believe you are probably correct and something I considered, but:

1. I'm not sure this is something I could ask the wife or kids to do if I'm not there.

2. The smallish (+/-4.5kW actual) power of the genset, still presents the 50Hz synchronization issue as loads fluctuate.

Can't you just take the genny input. Rectify it and input it on the one MPPT port as you would do with a wind TURBINE as it is shown in the manual. Limit the power to a kw size on the Sunsynk about 75% of genny full load. Much simpler. Sunsynk do show the series resistor and caps to be used as well as the max input from this DC source. The voltage that can be used is also shown. No worry about load or frequency from the genny.

Am I dreaming???

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2 hours ago, Scorp007 said:

Can't you just take the genny input. Rectify it and input it on the one MPPT port as you would do with a wind TURBINE as it is shown in the manual.

Eek. If you attempt this, make triple sure that your generator output is isolated, and can take high voltages with respect to earth. Most MPPT inputs are not isolated from earth, and have lethal voltages with respect to earth. That's without the generator operating.

Another thing is that the MPPT will attempt to maximise power consumption from what it assumes is a bunch of PV panels. It will not be expecting a very low impedance generator. 

I would not be attempting this, but good luck.

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25 minutes ago, Coulomb said:

Eek. If you attempt this, make triple sure that your generator output is isolated, and can take high voltages with respect to earth. Most MPPT inputs are not isolated from earth, and have lethal voltages with respect to earth. That's without the generator operating.

Another thing is that the MPPT will attempt to maximise power consumption from what it assumes is a bunch of PV panels. It will not be expecting a very low impedance generator. 

I would not be attempting this, but good luck.

Coulomb the input via MPPT for a wind generator is how Synsynk shows it in the manual.

In what way will a 3 phase AC genny from wind turbine differ from a single phase after being rectified. Just to add detail. The Sunsynk can accept 350/400V and 5kW on the 8kW model from a wind turbine in DC on its MPPT.

 

You can also look at the 1kW grid tied inverters with MPPT that can accept a battery load as an input to generate power after sunset. Different models based on the input voltage to MPPT.

It is a common reply that a MPPT would try to get the maximum power point but it seems not to be so in this case. Page 59 in the manual.

IMG_20220614_160101.thumb.jpg.d7a9d1a441bd6106f4a18f033a30621f.jpg

 

Edited by Scorp007
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On 2022/06/15 at 12:02 AM, Scorp007 said:

In what way will a 3 phase AC genny from wind turbine differ from a single phase after being rectified.

This is not my area of expertise, but I imagine that a [ wind ] generator as considerably more impedance than a generator. I also note that they include a resistance in the "simple circuit"; that resistor would have to be able to dissipate a lot of power (sometimes kilowatts). So this would be wasteful.

The other difference is that I assume that most wind generators would be isolated, and most generators would have a neutral to earth link, at least as sold. Such a link would short circuit parts of most transformerless inverters, and most of them are transformerless (transformerless in the sense of PV to output). Most inverters are transformerless these days; I'm 99% sure that the SunSynk are.

It concerns me that the SunSynk manual skimps over a lot of detail with the wind generator example. There is a reason that people use expensive, fit for purpose wind charge controllers.

With respect to allowing batteries at the MPPT inputs of some inverters: I wonder if they have special provision for that, or it's just another way to add a marketing dot point.

The purpose of my post was not necessarily to discourage you from trying this, but just pointing out that there is a lot to consider, and it may not be as simple as the manual suggests.

I was involved with a project that did feed DC from utility into an MPPT input; it's a bit of a long story. We didn't want significant power from it, it was to satisfy a safety requirement. We used an isolating transformer and something like a 100-300 W resistor, and the resistor was sized so that very little power would be available. Even at low power (of the order of 100 W), the transformer was heavy and expensive. From memory, it was a 3-phase transformer, and definitely a 3-phase inverter.

Edited by Coulomb
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"This is not my area of expertise, but I imagine that a generator as considerably more impedance than a generator. I also note that they include a resistance in the "simple circuit"; that resistor would have to be able to dissipate a lot of power "

Not sure what you try to say in the 1st sentence?

Yes the resistor is 1 ohm and 1kW rating as per the manual. Part of the point is some inverter can except such an input unlike a lot of others that cannot. Quite a major plus for the Sunsynk. Not all new way of using equipment need to be seen as sales talk.

It reminds me of a very big installer who told a friend who wanted a grid tied install without battery that no inverter can work without a battery. You MUST have a battery. He did go ahead and install the Solis but friend got no discount for providing training to the installer. 🤔🤔

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On 2022/06/15 at 5:49 PM, Scorp007 said:

Not sure what you try to say in the 1st sentence?

It was a perfectly edible word salad! 😳

I left out the word "wind" before the first use of "generator". Sigh.

A 1000 W rated resistor will be large, but I suppose in the scheme of things not too bad.

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I though about the same at one stage. What if you take a normal 48V lithium charger and attached that directly to your battery buss bar. You connect that to your 1kw generator  With that you can go up to around 20A charging. Maybe just as a backup to keep the batteries going through the night until solar pickups again.

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1 hour ago, Luminous said:

I though about the same at one stage. What if you take a normal 48V lithium charger and attached that directly to your battery buss bar. You connect that to your 1kw generator  With that you can go up to around 20A charging. Maybe just as a backup to keep the batteries going through the night until solar pickups again.

No problem with that. As long as your charger can be trusted and adhere to lithium levels. I am using an external MPPT on my Axpert from a solar panel at times. It saves the 600Wh/24hrs the Axpert wastes by just being on during its own MPPT doing the charging. I then only switch the Axpert on when needed. My main inverter is running as a grid tied. No PV goes to waste. This can be modified to be done remotely if needed.

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