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### Low Voltage From 12 Volt Inverter/Charger

06/23/2012 10:00 AM

I recently bought an inverter/charger which inverts 12v dc to 250 v AC 50hertz and can also invert 12v dc to 250 v AC.

After some time I discovered my 12v lead acid battery was failing after only working for 30 min. I first thought the charger was not delivering enough current, only to discover that it was outputting 11.88 volts instead of the expected 14 volts.

I checked inside and found four mosfets labelled IRFZ44N 119P TV.

1)what should i do to raise output voltage to 14 volts?

2) what is the minimum current needed to charge the battery, and how can i get it?

thanks

Pathfinder Tags: charger
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#1

### Re: low voltage from 12volt inverter/charger

06/23/2012 11:33 AM

Are you tryint to charge the battery from the inverter/charger that is being powered by that same battery?

If so the inverter/charger must draw more current from the battery than it can put back in if the efficency is less than 100%

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#4

### Re: low voltage from 12volt inverter/charger

06/23/2012 1:49 PM

No. what i mean is that when the Power Utility electricity is available,i charge my battery using the charging circuit of the inverter/charger.when there is a power failure i connect my battery to my inverter/charger and invert the dc using the invert circuit.that is when i discovered that the charging circuit is not producing enough voltage.

thanks

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#2

### Re: low voltage from 12volt inverter/charger

06/23/2012 11:37 AM

Are the four MOSFETS in a H bridge configuration to generate the 250 VAC through a transformer? What kind of topology is this inverter/charger? What percentage of the total stored energy was taken from the battery during inverter mode operation of 30 minutes? How long was the battery recharged? What does your hygrometer say about the electrolytes?

If these questions seem either irrelevant or you're incapable of answering them with certainty, hire a professional.

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#5

### Re: low voltage from 12volt inverter/charger

06/23/2012 2:03 PM

yes they are in an H bridge.

i dont know the topology.

the battery was recharged for 10 hours.

the electrolytes are ok for now

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#6

### Re: low voltage from 12volt inverter/charger

06/23/2012 3:36 PM

Well if the specific gravity measurement of the electrolyte measures "fine" then the battery is fully charged and your voltage reading is suspect. There is also the possibility that the low voltage reading is a combination of poor meter calibration and the charger circuitry sensing the battery is fully charged so it is not boiling water by applying a constant 14V. Maybe your hygrometer is not reporting accurately measuring all six cells.

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#3

### Re: low voltage from 12volt inverter/charger

06/23/2012 12:20 PM

It seems to me your charger is not working, it should be ~14.5 volts....This, or your power source isn't working or has a bad connection...

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#9

### Re: low voltage from 12volt inverter/charger

06/23/2012 3:48 PM

that was my point. so how do i repair the charger?

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#10

### Re: low voltage from 12volt inverter/charger

06/23/2012 4:47 PM

Well do you see that IC labeled U14 on the schematic? That's the charge regulating chip. You need to take your oscilloscope and read the duty cycle of the signal going to the charging transistor.

Oh, you probably should first look at the AC to DC power supply stage of the charger circuitry and determine if a voltage above the anticipated battery voltage exists. I'd expect that this is likely at least 15V but you might have some on board inductors that can be used to boost the voltage in a switch mode regulator approach.

I'd particularly look at the capacitor that stores charge between the 50 or 100 HZ cycles of your power grid cycles. Measuring the current draw there and comparing voltage droop across this capacitor will tell you with some analysis if the capacitor value has changed with time, a diode of your bridge, the capacitor is prematurely breaking down or a variety of other plausible failure modes can be revealed here.

Now take your available instruments and start looking at signals. Sketch out the circuit topology and start troubleshooting. You are the only one viewing this thread who can do this because you are the only one that that can touch this charger/inverter.

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#23

### Re: low voltage from 12volt inverter/charger

06/25/2012 4:49 PM

which schematic are you talking about,Redfred?

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#26

### Re: low voltage from 12volt inverter/charger

06/25/2012 5:00 PM

The schematic for a 12volt inverter charger, of course. Can't you see right there that the schematic number exactly matches the make and model number for your device. It has all of the exact same parts listed, in the exact same circuit topology as you mentioned. Well all except for the MOSFET model numbers you mentioned but they just work as a switch for the 50 HZ output.

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#28

### Re: low voltage from 12volt inverter/charger

06/25/2012 5:04 PM

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#30

### Re: low voltage from 12volt inverter/charger

06/25/2012 6:55 PM

You are correct. You are lost.

You never gave us a model number. You never gave us a schematic or circuit topology. How could I possibly have a schematic that matched your model number.

You never gave us any other node voltages but the output node voltage you correctly believe should exceed the battery voltage. You never gave us any indication that you understand how to follow any guidance in trouble shooting or that you have any instrumentation that can help you understand what is happening.

I tried to help you by getting you to think about what tools you have available. I tried to show you that the only important tool you can get here requires a conversation with questions and answers from both us and you.

You are correct. You are lost.

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#33

### Re: low voltage from 12volt inverter/charger

06/27/2012 2:47 AM

@redfred

thanks for your insight.But you seem to forget that the purpose of this forum is to share knowledge not brag about how smart we are or how many scientific accolades we possess.The moment you begin to think a question is irrelevant is the moment you should remove yourself from this forum and stop behaving like the moderator of this forum.

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#35

### Re: low voltage from 12volt inverter/charger

06/27/2012 8:02 AM

Now that's ironic. You instruct me on sharing on this forum when the root of my comment was your lack of sharing any feedback information. Sharing is a two way street. Giving and taking happen on one way streets. Now that we've shared this definition of cooperation I have a final question for you.

Why did you believe that this object that has no model name plate will charge a battery?

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#7

### Re: low voltage from 12volt inverter/charger

06/23/2012 3:41 PM

If you are reading charger volts while charging depleted battery, then this would be typical, as the charging voltage is relative to the charge level in the battery....In other words with the battery holding 20% charge, volts from charger typically between 11 and 12 volts....at 90% charge 12-13 volts...fully charged 13+ volts...

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#8

### Re: low voltage from 12volt inverter/charger

06/23/2012 3:47 PM

this is open-circuit voltage across the charger, with no load connected as yet

2
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#11

### Re: low voltage from 12volt inverter/charger

06/23/2012 10:34 PM

I would monitor it under load for several hours to see the results....

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#24

### Re: low voltage from 12volt inverter/charger

06/25/2012 4:51 PM

you could most probably be just draining the little charge in the battery

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#18

### Re: low voltage from 12volt inverter/charger

06/24/2012 4:49 PM

Some chargers will not charge if there is no load.

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#22

### Re: low voltage from 12volt inverter/charger

06/25/2012 4:47 PM

but this is a reading BEFORE i connect a load!there is no way the voltage reading is going to rise after connecting a load.

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#36

### Re: low voltage from 12volt inverter/charger

07/02/2012 7:00 AM

GA

Fully correct.

I don't think the OP has told us exactly all the battery specs either......

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#12

### Re: Low Voltage From 12 Volt Inverter/Charger

06/23/2012 10:43 PM

x

Score 1 for Off Topic
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#13

### Re: Low Voltage From 12 Volt Inverter/Charger

06/23/2012 10:49 PM

Marks the spot.

Eschew obfuscation.

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Off Topic (Score 5)
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#14

### Re: Low Voltage From 12 Volt Inverter/Charger

06/24/2012 3:18 AM

Your complaint is that the battery charge voltage is low, and yet the battery shows as fully charged? Or do I detect a complaint that the battery doesn't last long enough when making backup power?

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#15

### Re: Low Voltage From 12 Volt Inverter/Charger

06/24/2012 4:31 AM

If you are measuring 11.88V o/c on your charger output then it won't charge a battery.

Your charger is broken and needs to be fixed.

How to fix you ask? Bring it around to my shed and we can have a look together. Don't forget the beers and don't wake the dogs.

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#16

### Re: Low Voltage From 12 Volt Inverter/Charger

06/24/2012 9:14 AM

Are you testing the voltage open circuit or while it is connected to a discharged battery? The charger will charge the battery at a safe amperage which means that the more discharged the battery is the lower the input voltage will be to protect the battery from damage!

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#25

### Re: Low Voltage From 12 Volt Inverter/Charger

06/25/2012 4:57 PM

open circuit!!you guys! this charger does not have circuit to monitor battery voltage, so i expect the open circuit voltage in the region of 14-16 volts

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#17

### Re: Low Voltage From 12 Volt Inverter/Charger

06/24/2012 12:57 PM

а вот я использую такие зарядчики ... параллельно

? 90W + 150W

other words you have to kick that's it into full charge

it can start the 40W 386AT + 60W CRT (only when it's turned dim)
no matter my Celeron + it's CRT use 136W it can't start'em up
and it runs it 20 to 40 minutes depending the battery charge

- so i dont see an error you have to have inverter 2 or more times the
power consumed to start it up and not to get too hot in operation (thermal shut-down)

? "they" cant build a sh­­¡t really .. ? can "they"

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#19

### Re: Low Voltage From 12 Volt Inverter/Charger

06/25/2012 12:48 PM

Zener, is your inverter unit, 12dc to 250 ac, also actually a true battery charger or is it a 250vac to 12 dc power supply? If the later, the singular regulated voltage output of approx. 12 volts would not fully charge a battery but would give a minor charge, maybe enough to give that 1/2 hour use you mentioned.

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#27

### Re: Low Voltage From 12 Volt Inverter/Charger

06/25/2012 5:01 PM

Kendall you might be right.

maybe its a 12v dc power supply.but then whats the difference btwn a 12v dc power supply and a 12v charger?

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#34

### Re: Low Voltage From 12 Volt Inverter/Charger

06/27/2012 4:54 AM

what's the difference btwn a 12v dc power supply and a 12v charger?

A 12 V dc power supply has an output voltage of about 12V (11.88 would be quite normal), and, a 12V charger has a supply which ranges up to about 13.5V depending on the state of the battery.

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#37

### Re: Low Voltage From 12 Volt Inverter/Charger

07/02/2012 7:03 AM

Usually about 2 to 2.4 volts!!!!!

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#20

### Re: Low Voltage From 12 Volt Inverter/Charger

06/25/2012 3:18 PM

I am going to guess that the 11.88 volts is the average charger output without a battery connected. If so, try measuring the voltage with a battery on charge and see if the measurement doesn't increase to 13.5 to 15.0 VDC. Your meter is likely measuring the voltage droops near zero-crossing along with the peaks. It could be that the charger is working fine and the battery is just too weak to support extended operation.

An automotive type battery charger should output 10 to 12 amperes or so to support an inverter load of 100 watts. A typical fully charged car battery, say 60 ampere-hours, should discharge nearly flat in 5 hours at 10 amperes (100 watts load). Smaller batteries will obviously give corresponding shorter discharge times.

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#21

### Re: Low Voltage From 12 Volt Inverter/Charger

06/25/2012 4:41 PM

to TLC designer

yes its without a battery connected.but if i mmeasure with a battery connecred i will be measuring the voltage FROM the battery,coz there is no way the charger is going to increase its output just because a load has been connected across it.the charger is faulty because the battery is not being charged! hence my reason to seek help on the forum

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#29

### Re: Low Voltage From 12 Volt Inverter/Charger

06/25/2012 6:10 PM

Seems your unit is a inverter and converter, in one section taking 12 vdc input and creating 250 vac, and in the other taking 250 vac input with a regulated 12 vdc output to be used to power 12 volt dc equipment. A battery charger differs in that the output voltage goes higher than 12 volts, about 14.7 max, which is necessary to fully charge a normal lead acid battery. As I said earlier, the 12 volt regulated output will give a small charge to a depleted battery, but nowhere near a full charge.

BTW... What is the make and model of your unit?

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#31

### Re: Low Voltage From 12 Volt Inverter/Charger

06/25/2012 7:36 PM

I would just say buy a battery charger and be done with it. Or return it and get one that operates correctly. Read the name plate and see what the output should be. Maybe it is not a charger after all?

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#32

### Re: Low Voltage From 12 Volt Inverter/Charger

06/26/2012 1:47 AM

@jmart23

i think you have basically summarised it.i will have to buy a proper battery charger.

this unit does not have a name plate-seems to be a Chinese model.

But i have given the unit to someone to look it over-will update the forum on the outcome.

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