Understanding current flow

[BigBrosMo]

I have a 24v solar system set up and due to a few days of clouds I hooked up a 24v/20A charger. It doesn't seem to charge my bank nearly as fast as I was hoping for and so when measuring different things with my ammeter something has confused me. When everything is connected - there is some solar charging happening and the generator powered charger is running:

The red+ lead between the panels and the solar controller measures a negative current. (huh, why?)
The red+ lead between the controller and the batteries measure a positive current. (as I would expect)
The red+ lead between the batteries and the inverter measure a negative current. (as I would expect)
But when the red+ lead on the charger is measured between it and the batteries, it shows a negative current as well. Does that mean the charger is pulling current out of the batteries while the solar controller is putting it in? Or am I just misunderstanding current properly?

[dennis461]

what is battery bank size, number of batteries and make/model.
Could you sketch your wiring and post it?

[Sunking]

Or am I just misunderstanding current properly?

Yep plus you do not know how to measure current. Your meter has to be wired in series of the circuit under test to measure current. In other words it has to become a wire and part of the circuit. You cannot touch the leads to anything like you measure voltage. Do not try it because your meter likely has a 10 amp max limit, and if exceeded lets the magic smoke out. You can also get if you do not fully understand what you are doing. DIY SHOULD ONLY USE CLAMP ON METERS that do not require touching anything except the meter. PROS use Clamp On meters because using a series meter is a PIA, slow, and dangerous.

Only place DC Current can change directions in your circuit is the battery period no questions asked. Current from the chargers and to the load can only flow one-way from source to load period no questions asked.

If you have two sources like a generator and solar charge controller they will sum together but you have no control if the current goes to the battery, load or both. They go where the Law demands period no questions asked. That does not mean both sources will actually provide any current. The Stiffer Source, usually geny, will provide the greater share unless the batteries are discharged enough the genny cannot keep up or the voltage is set to lower than the solar controler. Keep in mind voltage does not charge batteries and is just a result of the batteries OCV plus current flowing.

Example if you have say a 12 volt 100 AH battery with a internal resistance .01 ohms and open circuit voltage of 12.1 volts. We connect a 10 amp charger set to 100 volts to the battery and turn it on, We measure the battery voltage and current. What do you measure and what happens?

Well you measure 12.1 volts and your battery is charging at 10 amps. If we stop charging several hours later when the voltage reaches 14.6 volts we have a vary happy fully charged battery period no question about it. Now if you do not terminate charge in time, after a couple of days will boil the water out of the battery and destroy it. What liquid is left is pure smoking hot sulfuric acid sludge thickened up from dissolved lead plates.

Also solve this problem please. You connect up a charger to a fully charged battery. How much charge current should you see?

Let me give you a hint. How much more water can you add to a full glass of water without spilling any or over flow?

[BigBrosMo]

what is battery bank size, number of batteries and make/model.
Could you sketch your wiring and post it?

That's all a bit irrelevant isn't it? I am trying to understand the current flow. Why would the make/model and capacity of my batteries have anything to do with the independent behavior of the loads/sources attached? Nonetheless, 4x160AH 12v 3K (Thai) Deepcycle batteries connected in series and parallel to give 24v in a load balanced wiring configuration. All loads/chargers positives to the same main positive, all negatives to the same main negative.

[BigBrosMo]

Yep plus you do not know how to measure current. Your meter has to be wired in series of the circuit under test to measure current. In other words it has to become a wire and part of the circuit. You cannot touch the leads to anything like you measure voltage. Do not try it because your meter likely has a 10 amp max limit, and if exceeded lets the magic smoke out. You can also get if you do not fully understand what you are doing. DIY SHOULD ONLY USE CLAMP ON METERS that do not require touching anything except the meter. PROS use Clamp On meters because using a series meter is a PIA, slow, and dangerous.

Only place DC Current can change directions in your circuit is the battery period no questions asked. Current from the chargers and to the load can only flow one-way from source to load period no questions asked.

If you have two sources like a generator and solar charge controller they will sum together but you have no control if the current goes to the battery, load or both. They go where the Law demands period no questions asked. That does not mean both sources will actually provide any current. The Stiffer Source, usually geny, will provide the greater share unless the batteries are discharged enough the genny cannot keep up or the voltage is set to lower than the solar controler. Keep in mind voltage does not charge batteries and is just a result of the batteries OCV plus current flowing.

Example if you have say a 12 volt 100 AH battery with a internal resistance .01 ohms and open circuit voltage of 12.1 volts. We connect a 10 amp charger set to 100 volts to the battery and turn it on, We measure the battery voltage and current. What do you measure and what happens?

Well you measure 12.1 volts and your battery is charging at 10 amps. If we stop charging several hours later when the voltage reaches 14.6 volts we have a vary happy fully charged battery period no question about it. Now if you do not terminate charge in time, after a couple of days will boil the water out of the battery and destroy it. What liquid is left is pure smoking hot sulfuric acid sludge thickened up from dissolved lead plates.

Also solve this problem please. You connect up a charger to a fully charged battery. How much charge current should you see?

Let me give you a hint. How much more water can you add to a full glass of water without spilling any or over flow?

Thanks Sunking for you response. I've seen from some of your posts you can be quite condescending and clearly I wasn't spared any reservation. Sigh... sometimes it's hard to just get straight help.

I am not sure why you said I don't know how to measure current. I do. I did. And that's why I asked my question. I used a clamp-on meter because as you said putting the voltmeter in series would be a pain in the ass and and also limited to 10A. I understand how to measure, I am not understanding the direction of flow.

I'll dumb it down for you so you can see I am not as dumb as you seem to think I am. The clamp-on shows a POS current on the red-positive lead connected between the solar controller and the batteries. The clamp-on shows a NEG current of exactly the same amount on the black-negative lead connected between the solar controller and the batteries. This is what would be expected and makes sense to me as it implies current is flowing from the controller into the batteries. The opposite shows on the clamp-on on the inverter. Which makes sense to me because it's implying that the energy from the batteries is flowing into the inverter as it draws power. What I don't understand is that when I connect the charger, it shows a NEG current on the red-positive lead connecting the charger to the batteries. Shouldn't it read like the solar controller... with the red-positive lead showing a positive reading as current flows from the charger to the batteries???

Your post-text about the full glass of water is not relevant here. The batteries are not full, that's why I put the charger on them. Please don't talk down to me - I know a thing or two about a thing or two.

[dennis461]

That's all a bit irrelevant isn't it? .

You posted this, ".. It doesn't seem to charge my bank nearly as fast.."
So i asked about the batteries.

Your charger will take 38+ hours to recharge those batteries, 640AH if it maintains 20 amps constantly.
You did not specify the make/model of charger, the plain jane variety do not maintain constant amperage, charging current t reduces as batteries come up to full charge, meaning it takes longer.

As for current direction, I'd like to see a sketch to see how everything is connected, if you've made a mistake somewhere, it may be easier for me to spot in a drawing versus interpreting written descriptions.

It seems if everything was connected correctly, and you can measure current properly ( it seems you can since you also posted, "as I would expect"), you should not see any negative current flow.

Now, with all that being said, what is the magnitude of the reverse current, small amounts could be explained, but not 5-10 amps.

[SunEagle]

You posted this, ".. It doesn't seem to charge my bank nearly as fast.."
So i asked about the batteries.

Your charger will take 38+ hours to recharge those batteries, 640AH if it maintains 20 amps constantly.
You did not specify the make/model of charger, the plain jane variety do not maintain constant amperage, charging current t reduces as batteries come up to full charge, meaning it takes longer.

As for current direction, I'd like to see a sketch to see how everything is connected, if you've made a mistake somewhere, it may be easier for me to spot in a drawing versus interpreting written descriptions.

It seems if everything was connected correctly, and you can measure current properly ( it seems you can since you also posted, "as I would expect"), you should not see any negative current flow.

Now, with all that being said, what is the magnitude of the reverse current, small amounts could be explained, but not 5-10 amps.

I didn't want to jump in and say anything to the OP but sometimes it is real easy to use the CT backwards.

There is usually an arrow on the CT that needs to be pointed toward the "load" that you are measuring. If you have it pointing toward the "source" you can get a negative value.

[J.P.M.]

Thanks Sunking for you response. I've seen from some of your posts you can be quite condescending and clearly I wasn't spared any reservation. Sigh... sometimes it's hard to just get straight help.

I am not sure why you said I don't know how to measure current. I do. I did. And that's why I asked my question. I used a clamp-on meter because as you said putting the voltmeter in series would be a pain in the ass and and also limited to 10A. I understand how to measure, I am not understanding the direction of flow.

I'll dumb it down for you so you can see I am not as dumb as you seem to think I am. The clamp-on shows a POS current on the red-positive lead connected between the solar controller and the batteries. The clamp-on shows a NEG current of exactly the same amount on the black-negative lead connected between the solar controller and the batteries. This is what would be expected and makes sense to me as it implies current is flowing from the controller into the batteries. The opposite shows on the clamp-on on the inverter. Which makes sense to me because it's implying that the energy from the batteries is flowing into the inverter as it draws power. What I don't understand is that when I connect the charger, it shows a NEG current on the red-positive lead connecting the charger to the batteries. Shouldn't it read like the solar controller... with the red-positive lead showing a positive reading as current flows from the charger to the batteries???

Your post-text about the full glass of water is not relevant here. The batteries are not full, that's why I put the charger on them. Please don't talk down to me - I know a thing or two about a thing or two.

I'm sure SK can amply speak for himself, but I wonder where your idea of condescension came from. I didn't see it. I think I did see a lot of what seems to be good information communicated in an objective manner.

Sometimes the perceived difference in abilities that serve as the kernel of embarrassment for some comes from the offended party's lack of confidence in their knowledge as much or more than from the offending party's confidence that's based on some knowledge that's incorrectly seen as arrogance.

People can only talk down to me if I choose to let them. I don't confuse having my ignorance reduced by straightforward, honest, and therefore what I see as respectful communication, with belittling.

Just sayin'.

[sdold]

I wonder where your idea of condescension came from. I didn't see it.

I think this happens because many (me included) sometimes assume things based on a lack of info. For instance I once asked about doing something with a 2000 (or maybe 4000) AH 12V battery. I had people telling me that it should have been 48V at that size and that I was nuts for using 12V. I could have taken it personally, but it was really my fault for not mentioning that it was a purpose-built system for 12V telecom loads. I didn't think it was an important piece just like the OP probably didn't think he'd need to explain that he'd used a clamp-on meter. Most of this is just misinterpretation.

[Mike90250]

That's all a bit irrelevant isn't it? I am trying to understand the current flow. Why would the make/model and capacity of my batteries have anything to do with the independent behavior of the loads/sources attached? Nonetheless, 4x160AH 12v 3K (Thai) Deepcycle batteries connected in series and parallel to give 24v in a load balanced wiring configuration. All loads/chargers positives to the same main positive, all negatives to the same main negative.

Because you are wanting help, For us to give you help, we need to understand the whole chain - maybe a wire got a wrap of red tape when it should have had black tape, but is still wired correctly.

Or you simply reversed the meter, but didn't realize it. So that's always the first thing comes to my mind, but I'm also sure you though of it too.
And all the perils of measuring amps, and hooking the meter into the explosive mode.

What you describe should not happen, several things come to mind, bad charge controller, letting the generator backfeed the panels, (common with a $5 ChiCom knockoff, rare with a morningstar)

[inetdog]

The nice thing about having a drawing is that you can talk about which way the arrow on the clamp (or the front face of the meter) is pointing when you make the measurement. That is, from one component toward another component rather than a physical direction.

When current is flowing into battery on the + lead with the arrow pointing toward the battery the current readout should be a positive number.
With the arrow pointing toward the battery on the - lead it should be a negative number.
If you put the charger on the other side of the battery bank physically, remember that you still need to point the arrow toward the battery to get consistent readings.

[Sunking]

Thanks Sunking for you response. I've seen from some of your posts you can be quite condescending and clearly I wasn't spared any reservation. Sigh... sometimes it's hard to just get straight help.

I was not condescending and fully answered your questions in great detail. Only one thing in your circuit can change current directions. Give you one last tip. With a 640 AH battery, your charge controller and panel wattage should be no less than 65 amps or you are pretty much doomed. You also need at least a 65 amp AC charger or more like 80 to 100 amps so you could actually fully charge your batteries in a day with a generator or commercial AC.

Have a nice day.

[Sunking]

For instance I once asked about doing something with a 2000 (or maybe 4000) AH 12V battery. I had people telling me that it should have been 48V at that size and that I was nuts for using 12V.

Who was that jerk?

Does not sound like anyone I would want to be friends with or could learn a thing from. Only 3 groups of people would ever use a 12 volt battery larger than 400 AH, DIY, HAM and LMR. One group knows what they are doing and why, another might or might not know what they are doing and why, and the other could use a little help.

Not sure who this guy is, but I did find one HAM who knows a little about grounding and wrote a nice 3-part article that applies to the subject matter. You can find Part 1 Installment here. The other two parts are Stickies right above Part 1 Installement.