I tried to charge my batteries by connecting a generator to an mppt and it didn't work. Why?

Gatet

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Dec 21, 2021
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Hello, I'm new. I signed up just to find this out. It's important for me. Sorry for any speech mistakes as English isn't my language.

So, I explain my problem.

I have a 12V solar installation with an mppt charger. I also have a generator and a battery charger that can charge at 12 and 24. Recently it's been very foggy for 2 weeks and also cold. All day the light intensity has been like that of the evening, so I've had to be using the generator.

The problem is that the battery charger charges very little. With very low batteries its ammeter shows about 7, but after some time it goes down to 2. I think the problem is the charger voltage is too low and it gets worse if the batteries are cold. So I've been wasting a lot of gasoline and in the morning the lights went off anyway.

So, as the battery charger can charge at 24 (you select it with a switch), I desconnected the solar panels from the mppt and connected the battery charger to the mppt thinking that it would adjust the 24V to the right voltage for the batteries. The mppt can manage an input voltage up to 100V.

But for some reason it doesn't work. Here is what happens. I switch the contraption on. The ammeter goes slowly up till it reaches about 12. Then it goes suddenly to 0. Goes up again to about 5 and again to 0. Then it keeps going up to about 3 and returning to 0, but staying at 0 most of the time. Batteries don't get charged at all.

It's all a big mistery to me. I guess the computer in the mppt does weird things for some reason.

Ok, that's the problem with my stuff. Thanks to anybody who can help me and have a nice day.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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For help we need information as no one here can read minds.
Type of Battery: Make, Model and related info, Link to product on web is always helpful.
Type of Solar Charge Controller: Make Model & Link to .
Make & Model of Inverter, Charger and other devices.

Normally, the SCC (Solar Charge Controller) only uses Solar Input, I have yet to see one take power from something else like a Generator.
AIO's (All In Ones) which contain the SCC, Inverter & Charger all in One Unit, that is another "animal" altogether.

The more detailed information you can provide about your setup the better the responses will be.
 

12VoltInstalls

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^^^all the above
But I can’t even wrap my mind around anything for even guessing without knowing what batteries you have and the specs on the battery charger.

So you’re plugging the battery charger into the generator and then putting the charging leads on the SCC solar input? Why not onto the battery terminals?
 

Gatet

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So you’re plugging the battery charger into the generator and then putting the charging leads on the SCC solar input? Why not onto the battery terminals?
Hi, sorry, I didn't explain myself. Yes, I plug the battery charger into the generator. Also, I did try to put the charging leads onto the battery terminals but, as I explained, it charges very little. That's why I tried the other way.

My 2 batteries are this:
rolls-battery-s460.jpg


My SCC:

victron-bluesolar-mppt-100-30-12v-24v-30a-90896-1-67-008530_600x600.jpg

The battery charger is a very basic car battery charger with an ammeter and normal/boost speeds both of which I tried.
 

wholybee

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The MPPT adjusts itself to find the maximum wattage it can get from the panels. It expects that as it increases current, the voltage from the panel will reduce. It finds the balance of panel voltage and panel current that produces the most wattage.

The battery charger probably has bulk, absorb, and float stages for whatever type of battery is is set for, and expects to have a battery as a load.

These devices a smart enough that using them not as intended can have weird results. I would never connect them as you have. I don't know what they would do, but i expect they will not work

You probably just need a new/correct charger. Did i miss what model you have? Is it setup correctly for you specific battery?

I am not experienced with Rolls, but i think they take different settings than typical deep cycle batteries.
 

12VoltInstalls

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You need at least a 30A charger. Even a 200Ah 12V battery at 50% charge would take 4+ hours to recharge on 30A of charge. They key is not letting them fall too low.

So if you have a 10A or worse 1- or 2A charger you won’t see much of a change.

Are the batteries electrolyte levels ’full’ over the plates?
 

Hedges

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30A MPPT SCC, probably enough to handle what battery charger can put out.
Some battery chargers have a degree of functionality beyond just transformer/rectifier. It is possible charger isn't holding voltage.
MPPT algorithm looks for maximum power, might have trouble with I/V curve coming from battery charger. Might hurt itself if too much current is available.

I've put a resistor or automobile headlight bulb in series with a charger to reduce current for a small battery. You could try that; what it would do is give a different I/V curve that is closer to what PV panels produce.

Power from battery charger follows a rectified sine wave, 50 or 60 Hz. would expect capacitors in SCC to smooth that, but maybe not - they expect constant current source.

With very low batteries its ammeter shows about 7, but after some time it goes down to 2. I think the problem is the charger voltage is too low and it gets worse if the batteries are cold.

Lead-acid batteries do need to charge at higher voltage when cold (does SCC have a temperature sensor?)

Here's a thought: You have 6V batteries, 12V battery charger. If you disconnect batteries and wire them in parallel as a 6V bank, the battery charger would put high current into them. You would have to monitor voltage and terminate charge manually or they would eventually overcharge. If it is a 10A charger and you have 2x 200AH batteries, would be 40 hours from completely empty. (I hope you have a low-battery shutdown in the inverter or loads. It is bad for battery to get heavily discharged.)

Do you have any spare transformers? If you could boost AC voltage a bit, should charge better. A 120V to 12V transformer could be wired in series as an auto-transformer to produce 132V.

If you turn generator speed up it will probably deliver higher voltage as well as higher frequency. Assuming a basic generator, not inverter model.

If an inverter generator, maybe it produces "Modified Sine Wave" (which I call Modified Square Wave), having peaks that aren't as high so rectified output of battery charger is not high enough voltage.
 

Don B. Cilly

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So you’re plugging the battery charger into the generator and then putting the charging leads on the SCC solar input? Why not onto the battery terminals?

He thought that doubling the voltage (the charger can do 24V) the SCC could double the amps.
Which makes sense, it could, and it should.
The battery charger being "very basic", puts out a pulsating DC which will charge the battery but obviously confuses the SCC.

The only solution seems to be to get a bigger 12V charger.
 

wholybee

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He thought that doubling the voltage (the charger can do 24V) the SCC could double the amps.
Which makes sense, it could, and it should.
The battery charger being "very basic", puts out a pulsating DC which will charge the battery but obviously confuses the SCC.

The only solution seems to be to get a bigger 12V charger.
Reading now that he has one of those automotive charge/boost types, he needs not just bigger, but a proper charger for deep cycle batteries. The chargers i have seen like he described are a simple trickle charger. The OP should buy a good 3 stage charger for a deep cycle. If he wants to minimize generator run time, then a large one.
 

Hedges

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I also have a generator and a battery charger that can charge at 12 and 24. ...

So, as the battery charger can charge at 24 (you select it with a switch),

Oh, instead of rewiring battery for 6V, just set battery charger to 24V and charge the 12V system with that.
Lead-acid battery will clamp voltage to about 16V max during equalization. But instead manually stop at whatever proper charge voltage is, like 15V.

For future use, maybe you can get a nice automatic battery charger. Some are "high frequency" meaning switching power supply, which should deliver correct voltage regardless of AC input voltage variations. And hopefully not care about square wave from an inverter generator, if that's what you've got.
 

HRTKD

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@Gatet , you need an AC-DC converter. The typical converter will charge at a much higher amperage rate than a regular automotive battery charger. The converter I use in my RV charges at 55 amps.
 

Bud Martin

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It sounds like the battery charger may be one of those simple transformer with bridge rectifier and no filter caps, so the output is pulsing D.C. that is twice the line frequency. Make and model of the charger?
 

Gatet

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Oh, instead of rewiring battery for 6V, just set battery charger to 24V and charge the 12V system with that.
Lead-acid battery will clamp voltage to about 16V max during equalization. But instead manually stop at whatever proper charge voltage is, like 15V.

I think that doing that might fuse the 15A fuse on the charger. But I may try it anyway.
 

Hedges

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Your basic charger has a fuse?
Probably the fuse doesn't blow at current it can produce, only if charger gets shorted inside and battery dumps into it.
Possibly charger will get too hot. But on normal not boost setting, maybe not. Blow air into it if you have a fan.

Would expect a battery charger to charge FLA reasonably full. I'm wondering if your generator is inverter type and puts out MSW. In that case, peak of waveform probably lower than peak of a sine wave would be, so transformer type charger doesn't deliver as high a voltage.
 

Gatet

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Your basic charger has a fuse?
Probably the fuse doesn't blow at current it can produce, only if charger gets shorted inside and battery dumps into it.
Possibly charger will get too hot. But on normal not boost setting, maybe not. Blow air into it if you have a fan.
2 fuses in fact. One for AC and another for DC.
Would expect a battery charger to charge FLA reasonably full. I'm wondering if your generator is inverter type and puts out MSW. In that case, peak of waveform probably lower than peak of a sine wave would be, so transformer type charger doesn't deliver as high a voltage.
No idea about any of that. I think the generator is the typical one with an alternator on the same axle as the engine.
 

Gatet

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Dec 21, 2021
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It sounds like the battery charger may be one of those simple transformer with bridge rectifier and no filter caps, so the output is pulsing D.C. that is twice the line frequency. Make and model of the charger?
20211229_165717.jpg
 
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