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Old 08-08-2016, 14:31   #1
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Measuring Amps and Watts

I purchased 2 volt, amp, watt meters.

My 50 watt solar panel is definitely charging my 35ah battery, but the meter only reads the voltage of the battery.

The meter on the other side of the battery, connected before the inverter measures the watts and amps (as well as battery voltage), but I only get 0.00 (amps and watts) when connected between the charge controller and the battery. This meter also measures the battery voltage fine, but nothing else. This meter works fine when connected to the inverter side so it is not broken.

I know you need to measure amps in series, but I am sure the meter is internally designed to do this as it measures it correctly with the inverter.

The battery is charging and I can measure 19v at the solar panel positive and negative screws.

Also, it seems to take 2 full days of sun to completely charge the 35ah battery with a 50 watt solar panel. Does this seem correct? I hear many people on boats saying their battery banks are filled by 10am.
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Old 08-08-2016, 14:56   #2
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Re: Measuring Amps and Watts

It may be that the meter doesn't like the pwm current coming from the controller (wag on my part).

As far as taking two days to charge.... That's not unheard of, your 50 watt panel won't put out 50 watts for long unless you follow the sun with it. Others that have said they're full by 10am are in the tropics with 800-1200 watt solar arrays.


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Old 08-08-2016, 14:58   #3
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Re: Measuring Amps and Watts

OK, is there a shunt? Maybe it can measure small current if wired into the circuit, but to measure any significant current I think your going to need a shunt.
Do not believe people who say the batteries are recharged by 10 am, I am not saying they are not telling the truth, just they don't understand that when the battery reaches say 13 V while being charged that does not mean it is charged, they think it does.


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Old 08-08-2016, 15:13   #4
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Re: Measuring Amps and Watts

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Originally Posted by a64pilot View Post
OK, is there a shunt? Maybe it can measure small current if wired into the circuit, but to measure any significant current I think your going to need a shunt.
Do not believe people who say the batteries are recharged by 10 am, I am not saying they are not telling the truth, just they don't understand that when the battery reaches say 13 V while being charged that does not mean it is charged, they think it does.


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In the right weather our batteries are sometimes charged by 11am-midday. That's not at 13 volts, that's when the charge controller has hit 14.2 volts (LiFEPO4's) then switched to float.


But that's replacing maybe 100 a/h off 800 Watts solar. You'd expect charging 35 ah off 50 Watts would take longer.
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Old 08-08-2016, 15:22   #5
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Re: Measuring Amps and Watts

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In the right weather our batteries are sometimes charged by 11am-midday. That's not at 13 volts, that's when the charge controller has hit 14.2 volts (LiFEPO4's) then switched to float.


But that's replacing maybe 100 a/h off 800 Watts solar. You'd expect charging 35 ah off 50 Watts would take longer.

I don't know about lifepo4 as you have a different acceptance rate, usually unless specified, it's some kind of LA battery we discuss and acceptance rate is the issue with them, I can have a 10,000 W array charging a 100 AH bank of LA batteries and if they were discharged much at all, they aren't going to be charged by 10 AM.
On a LA bank, float doesn't necessarily mean close to full charge either, my alternator will go to float with my batteries at 80% or so, which of course is way early, I need to find a way I can lock it into absorption.


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Old 08-08-2016, 16:54   #6
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Re: Measuring Amps and Watts

google images of ammeter wiring diagrams. it must have the correct load to read accurately. slow charge has many reasons: cloudy days, poor angle of panels towards sun, shading by boat gear, tired batteries, inefficientcharge controller, corrosion, thin wires creating high reistance, latitude, how deeply you have discharged the batteries, load on batteries from boat appliances as you charge and more. compare your system with similar ones not ones that generate many times more power than required. you need to generate enough power to last for the day. The rest is waste.
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Old 08-08-2016, 16:54   #7
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Re: Measuring Amps and Watts

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OK, is there a shunt? Maybe it can measure small current if wired into the circuit, but to measure any significant current I think your going to need a shunt.
No, it doesn't have a shunt. The meter measuring from the 35ah battery to the inverter measures 24 watts at 0.35amps.

I calculate 50 watts/12v = 4.2amps or about 3.3 amps from a pwm controller since they are only 80% efficient.

I guess I will have to order a DC amp clamp and see if that works.
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Old 08-08-2016, 17:06   #8
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Re: Measuring Amps and Watts

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Originally Posted by lindabarzini View Post
Also, it seems to take 2 full days of sun to completely charge the 35ah battery with a 50 watt solar panel. Does this seem correct? I hear many people on boats saying their battery banks are filled by 10am.
A 50 Watt panel will generate about 20Ah per day at best.
Which is unlikely to put more than 15Ah back into your batteries for various reasons. So yes, if you run your battery down, it will take more than a day to recharge.

Don't believe anyone who says their battery banks are filled by 10am unless they have exotic batteries such as LiFePo4 and a big solar array. If they are using Lead Acid batteries, that just ain't going to happen.
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Old 08-08-2016, 17:20   #9
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Re: Measuring Amps and Watts

That unit has a built-in shunt. I have the V-A (only) version of the same and it works fine.

Not sure, but it may be sensitive to the load polarity. Try swapping the load leads and let us know.
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Old 08-08-2016, 17:21   #10
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Re: Measuring Amps and Watts

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Originally Posted by lindabarzini View Post
No, it doesn't have a shunt. The meter measuring from the 35ah battery to the inverter measures 24 watts at 0.35amps.

I calculate 50 watts/12v = 4.2amps or about 3.3 amps from a pwm controller since they are only 80% efficient.

I guess I will have to order a DC amp clamp and see if that works.
The shunt is built into the unit. So amps to 20 amps is measured by connecting the wire from one leg of the charge controler output to one of the outer terminals and the other outside terminal connects to the battery. Though it's unclear on the Ebay sellers listing if it works that way. The meter is designed to measure load of a device. It should work with solar (power generation, but there is a odd chance it might not. A pain I know
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Old 08-08-2016, 17:25   #11
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Re: Measuring Amps and Watts

The voms: you must have connected something wrong. Look up the wiring diagram, check your connections.

These are fly by units you do need one each side of the battery. The shunt is inside.

Q2A2: Panel 50W rated at say 16V hence max A say 50/16 say 3A. A good sunny location is 5 to 6 sun/hours (max). 5.5hrsx3A = 16.5 A (max)

Two sunny days = 32A (max). Deduct loses get 25 (max). You could be able to fully charge a 50Ah batt with that ("fully discharged" = 50% down)

Yes a bit slow. But nothing to worry about. A single odd cloud can reduce panel output by more than 50% rated value.

CAN YOU ANGLE YOUR PANELS?

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Old 08-08-2016, 17:29   #12
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Re: Measuring Amps and Watts

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Originally Posted by lindabarzini View Post
I know you need to measure amps in series, but I am sure the meter is internally designed to do this as it measures it correctly with the inverter.
To measure current, your measuring device needs to /be/ the path the current is flowing through.
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Old 08-08-2016, 22:11   #13
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Re: Measuring Amps and Watts

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To measure current, your measuring device needs to /be/ the path the current is flowing through.
Shunt? Hall effect DC clamp meter?
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Old 09-08-2016, 01:20   #14
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Re: Measuring Amps and Watts

everybody treat themselves to one of those:
https://www.amazon.com/Best-Sellers-...ial/5011680011

8attention: not all measure A DC!)
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Old 09-08-2016, 03:11   #15
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Re: Measuring Amps and Watts

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Originally Posted by a64pilot View Post
I don't know about lifepo4 as you have a different acceptance rate, usually unless specified, it's some kind of LA battery we discuss and acceptance rate is the issue with them, I can have a 10,000 W array charging a 100 AH bank of LA batteries and if they were discharged much at all, they aren't going to be charged by 10 AM.
On a LA bank, float doesn't necessarily mean close to full charge either, my alternator will go to float with my batteries at 80% or so, which of course is way early, I need to find a way I can lock it into absorption.


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True. The LiFEPO's are pretty much fully charged (say 95% +) when they hit 14 and a bit volts. And they'll accept just about whatever you can feed them up till then.

Lead acids need to absorb for a while, so current will be reduced, so time increased..
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