Battery pulling down panel voltage???

Virtuousdesires · March 2017

What I am working with (For now):

1.) 2 100 watt panels wired in parallel 25 feet from charge controller using 10 AWG wire.

2.) Morningstar TriStar PWM 60 set for 12 (14.6) volts, 4 feet from batteries using 2 AWG cable.

3.) 2 new DEKA group 31 flooded batteries fully charged before use (210 AH total).

Hope that's enough info for this question.

I discharged my batteries to around 70 percent (1.225 on hydrometer@12.3 volts) and noticed my charge controller only putting out about a volt above my battery voltage (about 13.3 volts). The Amperage was good though around 10.5 amps.

As the batteries were charging (No, there was no load during charging) I did notice the voltage creep up accordingly as they charged. But those batteries were being charged all day up to 13.5 volts (According to my trimetric meter and display on the Morningstar). But when I checked with the hydrometer nothing changed much, still hovering around 1.225.

That's below the 14.6 charge setpoint I put in. When the batteries were charged it went through the PWM mode then into float.

I did shut the system down and checked the open circuit voltage with no load and got 22 something volts on each panel.

My question is, is it normal for a discharged battery to pull the panel voltage down below my setpoint of 14.6 but leave the amps full throttle? I am new to this and this is my first run after much research

If that is normal, that tells me 200 watts of solar power is not nearly enough to charge a 210 AH battery bank. Am I right?

Will more panels bring the voltage up to charge faster?

I tried most of the day yesterday to find an answer and couldn't, so now I'm here on a forum.

Edit: There was no shade on the panels what so ever. Also I live near Detroit Michigan.

westbranch · March 2017

Virtuousdesires said:

What I am working with (For now):

1.) 2 100 watt panels wired in parallel 25 feet from charge controller using 10 AWG wire.

2.) Morningstar TriStar PWM 60 set for 12 (14.6) volts, 4 feet from batteries using 2 AWG cable.

3.) 2 new DEKA group 31 flooded batteries fully charged before use (210 AH total).
...........
My question is, 1) is it normal for a discharged battery to pull the panel voltage down below my setpoint of 14.6 but leave the amps full throttle? I am new to this and this is my first run after much research

If that is normal, that tells me 200 watts of solar power is not nearly enough to charge a 210 AH battery bank. 2) Am I right? 3)Will more panels bring the voltage up to charge faster?

1) Yes 2) Yes 3) Yes
When a battery is well depleted it will take a long time for the amps to get high enough that the volts starts to rise. When there is enough internal resistance to the Amps available the volts will start to rise and you will enter Absorb phase. This is a lesson in what you get without enough panels... it may take several days for your batteries get filled... You could figure out the number of watts or Ahrs of power you have used and then use 4 hrs of good sunshine per day to estimate how long the recharge will take... But in the mean time go out and find 2 more identical panels.... to add to the setup.hth

Virtuousdesires · March 2017

westbranch said:

Virtuousdesires said:

What I am working with (For now):

1.) 2 100 watt panels wired in parallel 25 feet from charge controller using 10 AWG wire.

2.) Morningstar TriStar PWM 60 set for 12 (14.6) volts, 4 feet from batteries using 2 AWG cable.

3.) 2 new DEKA group 31 flooded batteries fully charged before use (210 AH total).
...........
My question is, 1) is it normal for a discharged battery to pull the panel voltage down below my setpoint of 14.6 but leave the amps full throttle? I am new to this and this is my first run after much research

If that is normal, that tells me 200 watts of solar power is not nearly enough to charge a 210 AH battery bank. 2) Am I right? 3)Will more panels bring the voltage up to charge faster?

1) Yes 2) Yes 3) Yes
When a battery is well depleted it will take a long time for the amps to get high enough that the volts starts to rise. When there is enough internal resistance to the Amps available the volts will start to rise and you will enter Absorb phase. This is a lesson in what you get without enough panels... it may take several days for your batteries get filled... You could figure out the number of watts or Ahrs of power you ahve used and then use 4 hrs of good sunshine per day to estimate how long the recharge will take... But in the mean time go out and find 2 more identical panels.... to add to the setup.hth

I probably did more research than a lot of newbies do but I'm still getting spanked! Lol I had already set my mind not to expect too much from a solar system within my budget. I know for example those aren't the best batteries to use, but I figured if I ruined them it's better than ruining some Trojan batteries.

Thanks so much for your reply!

Johann · March 2017

Virtuousdesires said:

westbranch said:

Virtuousdesires said:

What I am working with (For now):

1.) 2 100 watt panels wired in parallel 25 feet from charge controller using 10 AWG wire.

2.) Morningstar TriStar PWM 60 set for 12 (14.6) volts, 4 feet from batteries using 2 AWG cable.

3.) 2 new DEKA group 31 flooded batteries fully charged before use (210 AH total).
...........
My question is, 1) is it normal for a discharged battery to pull the panel voltage down below my setpoint of 14.6 but leave the amps full throttle? I am new to this and this is my first run after much research

If that is normal, that tells me 200 watts of solar power is not nearly enough to charge a 210 AH battery bank. 2) Am I right? 3)Will more panels bring the voltage up to charge faster?

1) Yes 2) Yes 3) Yes
When a battery is well depleted it will take a long time for the amps to get high enough that the volts starts to rise. When there is enough internal resistance to the Amps available the volts will start to rise and you will enter Absorb phase. This is a lesson in what you get without enough panels... it may take several days for your batteries get filled... You could figure out the number of watts or Ahrs of power you ahve used and then use 4 hrs of good sunshine per day to estimate how long the recharge will take... But in the mean time go out and find 2 more identical panels.... to add to the setup.hth

I probably did more research than a lot of newbies do but I'm still getting spanked! Lol I had already set my mind not to expect too much from a solar system within my budget. I know for example those aren't the best batteries to use, but I figured if I ruined them it's better than ruining some Trojan batteries.

Thanks so much for your reply!

Nobody is going to spank you here, just good ole folks trying to help you and trying to protect your equipment so it will last longer.

The better way to check the state of charge is after the battery been sitting for a few hour without charging or discharging the battery. This way the surface charge on the plate is dissipated and you will see a truer state of charge.

200 watt of solar panels, will still give you enough power for LED lighting at night or in emergencies and power for other small electrical items/things as long as you watch your power usage a bit.

Virtuousdesires · March 2017

Johann said:

Virtuousdesires said:

westbranch said:

Virtuousdesires said:

What I am working with (For now):

1.) 2 100 watt panels wired in parallel 25 feet from charge controller using 10 AWG wire.

2.) Morningstar TriStar PWM 60 set for 12 (14.6) volts, 4 feet from batteries using 2 AWG cable.

3.) 2 new DEKA group 31 flooded batteries fully charged before use (210 AH total).
...........
My question is, 1) is it normal for a discharged battery to pull the panel voltage down below my setpoint of 14.6 but leave the amps full throttle? I am new to this and this is my first run after much research

If that is normal, that tells me 200 watts of solar power is not nearly enough to charge a 210 AH battery bank. 2) Am I right? 3)Will more panels bring the voltage up to charge faster?

1) Yes 2) Yes 3) Yes
When a battery is well depleted it will take a long time for the amps to get high enough that the volts starts to rise. When there is enough internal resistance to the Amps available the volts will start to rise and you will enter Absorb phase. This is a lesson in what you get without enough panels... it may take several days for your batteries get filled... You could figure out the number of watts or Ahrs of power you ahve used and then use 4 hrs of good sunshine per day to estimate how long the recharge will take... But in the mean time go out and find 2 more identical panels.... to add to the setup.hth

I probably did more research than a lot of newbies do but I'm still getting spanked! Lol I had already set my mind not to expect too much from a solar system within my budget. I know for example those aren't the best batteries to use, but I figured if I ruined them it's better than ruining some Trojan batteries.

Thanks so much for your reply!

Nobody is going to spank you here, just good ole folks trying to help you and trying to protect your equipment so it will last longer.

The better way to check the state of charge is after the battery been sitting for a few hour without charging or discharging the battery. This way the surface charge on the plate is dissipated and you will see a truer state of charge.

200 watt of solar panels, will still give you enough power for LED lighting at night or in emergencies and power for other small electrical items/things as long as you watch your power usage a bit.

Oh, I meant spanking as in karma kind of thing, not by the forum members! Lol I really do appreciate any advice and I don't mind correction. Yeah, of all the reading I have done there's so much more to learn still, that's what I mean.

As far as the batteries sitting for a bit after a charge, does the apply to the Specific gravity check as well? I know a voltmeter isn't accurate after a charge.

As far as watching my usage, I bought a 2030 RV trimetric meter from Bogart Engineering, love that little gadget. I think I have to further tweak the settings on it though.

Estragon · March 2017

You don't need to let batteries rest much for SG. I like to wait for them to stop bubbling before opening caps just to avoid splashing though.

mcgivor · March 2017

Estragon said:

You don't need to let batteries rest much for SG. I like to wait for them to stop bubbling before opening caps just to avoid splashing though.

Depending on the temperature, the SG readings may well be lower than, if left to cool, or perhaps a temperature compensated reading would be appropriate, yes/no

Estragon · March 2017

Temp compensation would be appropriate would be appropriate if battery is warm/cool for whatever reason, like if ambient is 40C+

mcgivor · March 2017

Estragon said:

Temp compensation would be appropriate would be appropriate if battery is warm/cool for whatever reason, like if ambient is 40C+

For example, after an equalization, the temperature of the battery may well be higher than the ambient temperature.

Estragon · March 2017

Could be. Mine are usually quite cool and charging usually just gets them to around room temp.

mcgivor · March 2017

Yes, depending on location, I'm tropical, so temperatures are generally higher to start with and ambient temperature plays in a negative effect for me, location is a factor.

mike95490 · March 2017

PWM controllers connect the PV (a limited current source) directly to the batteries (a nearly infinite sink) so when the batteries are low, the panels will read the same as the battery voltage (the controller is now a direct connection) So battery voltage IS expected to be seen on PV side of things, when batteries are charging at max.
A MPPT controller is "smarter" and works like a transformer, and harvests the voltage delta between battery voltage and panel voltage and is more efficient.

Virtuousdesires · March 2017

mike95490 said:

PWM controllers connect the PV (a limited current source) directly to the batteries (a nearly infinite sink) so when the batteries are low, the panels will read the same as the battery voltage (the controller is now a direct connection) So battery voltage IS expected to be seen on PV side of things, when batteries are charging at max.
A MPPT controller is "smarter" and works like a transformer, and harvests the voltage delta between battery voltage and panel voltage and is more efficient.

I'm still trying to wrap my head around how exactly MPPT works. Is it better to take say 500 watts of 100 watt solar panels connected in series to bring up the voltage? If so, it seems I would only end up with 5 amps (Just as example). I hoping to have 10x100 watt panels, what would be the best way to hook those to an MPPT controller for a 12 or 24 volt system? Can you give me an example of both? ( I still haven't made my mind up about 12 or 24 volts only working with a thousand watts)

littleharbor2 · March 2017

Considering you can get a thousand watts in 3 to 4 panels @ approx. 50 cents a watt why would you want to use 10 expensive 12 volt panels? You have Way less connections, no fusing or combiner box to buy. The beauty of an MPPT controller is you can save money with the larger, cheaper panels.

Virtuousdesires · March 2017

littleharbor2 said:

Considering you can get a thousand watts in 3 to 4 panels @ approx. 50 cents a watt why would you want to use 10 expensive 12 volt panels? You have Way less connections, no fusing or combiner box to buy. The beauty of an MPPT controller is you can save money with the larger, cheaper panels.

They don't appear much cheaper when shipping is factored in. I also want the compact size because there's a chance I may choose to live out of an RV or van and have more options with smaller 100 watt panels, or so it would seem. Lol I'll take another look though and compare prices. I am kind of limited in the system size because I live in a mobile home park as well. I figured an MPPT charge controller would be a waste of money for such a small system. I don't want to buy just to say I have it. Also with a smaller system I wanted to take my limited funds and pay the high dollars for a Magnum inverter (Someday) with the remote panel and built in charger. If I am wrong in my assumption I am willing to be corrected!

Also, I did actually plan on buying a combiner box with breakers. I do know when I install the system I would like it to be nec compliant to pass inspection. I don't even know if I should try to pull a permit or not. Probably get fined if I didn't...

Virtuousdesires · March 2017

littleharbor2 said:

Considering you can get a thousand watts in 3 to 4 panels @ approx. 50 cents a watt why would you want to use 10 expensive 12 volt panels? You have Way less connections, no fusing or combiner box to buy. The beauty of an MPPT controller is you can save money with the larger, cheaper panels.

Where do you recommend pricing out the panels? Where are you seeing them near 50 cents a watt?

Vic · March 2017

Virtuous..,

Here is some info on the operation of MPPT CCs:
https://www.solar-electric.com/mppt-solar-charge-controllers.html/

Vic

littleharbor2 · March 2017

Virtuousdesires said:

littleharbor2 said:

Considering you can get a thousand watts in 3 to 4 panels @ approx. 50 cents a watt why would you want to use 10 expensive 12 volt panels? You have Way less connections, no fusing or combiner box to buy. The beauty of an MPPT controller is you can save money with the larger, cheaper panels.

Where do you recommend pricing out the panels? Where are you seeing them near 50 cents a watt?

This isn't something I have shared here for obvious reasons but I sell solar panels and have new 255 to 310 watt panels for 49 cents a watt. Look on your local craigslist. Buy local and avoid shipping altogether.There seems to be a shipload of people selling these days in this price range.

Virtuousdesires · March 2017

> @Vic said:
> Virtuous..,
>
> Here is some info on the operation of MPPT CCs:
> https://www.solar-electric.com/mppt-solar-charge-controllers.html/
>
> Vic

So just for example, my 2 100 watt panels was putting out 10.5 amps at 13.5 volts (Around 150 watts according to the display). If I wired the two panels in series to make 24 volts and used an mppt charge controller set to 12 volts (14.6), what might those numbers look like? More voltage and amps going into the battery? Seems like how that works.

Estragon · March 2017

@Virtuousdesires
There are a couple of advantages to MPPT controllers, but neither may apply in your application:
1. You can use higher voltage panels, which tend to be bigger and more costly to ship, but which are produced and shipped in high volume, so MAY be more cost effective locally to you.
2. You can wire panels in higher voltage strings, which is an advantage if panels are a long distance from controller. Higher voltage with lower amperage is the same wattage but allows the use of smaller wire for less wire loss.

In a camper/rv application you won't be going far from panel to controller, so if you have to use a bigger wire to minimize wire losses it probably isn't a big deal. That may take care of the second advantage. The first advantage may or may not apply depending on what's available locally.

Using your 500w example - a 100w 12v nominal panel will be around 18Vmp and 100w/18v=5ish amps.

You could wire in parallel, which would be 5*5a=25a@18v=450w. You could use a PWM controller for this, but wouldn't want to go far to minimize wire losses.

You could wire in series, which would be 5*18v=90v@5a=450w. You would use a MPPT controller for this to reduce the ~90v to charging voltage.

Either way, you get 450w +/- out of the panels.

It's not a question of what's "better". It's just what works for the application.

littleharbor2 · March 2017

Except your batteries will pull that Paralleled 18 volts down to just above their voltage so that 18 volts goes down to say 12.3 volts while charging and will rise up to say 14.6 when near full. Problem is that voltage differential is lost with a PWM controller. With a MPPT controller it takes that high voltage and steps it down to your batteries desired voltage, (while the amperage rises in unison), without losing any of the differential. You will lose potential power with a PWM controller and your batteries wont see that full 500 , or whatever watts.

Photowhit · March 2017

Virtuousdesires said:

So just for example, my 2 100 watt panels was putting out 10.5 amps at 13.5 volts (Around 150 watts according to the display). If I wired the two panels in series to make 24 volts and used an mppt charge controller set to 12 volts (14.6), what might those numbers look like? More voltage and amps going into the battery? Seems like how that works.

No it will be similar, MPPT is not super cost effective with 1000 watt or less systems, there might be a 10% advantage, in general, likely even better when cold.

Where are you located?

SolarBLVD.com and SunElec.com are wholesalers, but you can make poor buying choices as they aren't customer service oriented, but have cheapest prices in general, I'll add another if you wanted pallet quantities. Stay away from Thin film panels! If asking for a quote including shipping, be sure to give them all pertinent information, or you may be ignored. With shipping you want to list address, if it's a home or business, if someone will be there, if a lift gate is needed or loading dock...

mike95490 · March 2017

So just for example, my 2 100 watt panels was putting out 10.5 amps at 13.5 volts (Around 150 watts according to the display). If I wired the two panels in series to make 24 volts and used an mppt charge controller set to 12 volts (14.6), what might those numbers look like? More voltage and amps going into the battery? Seems like how that works.

Can't tell. The PWM has corrupted the the PV potential output. But taking a long shot, you have 200W @ 18V = 11A Which is pretty close to the 10.5A you currently measure. So, using poisoned numbers, and guessing wildly, you gain at least 1/2 amp, which is about full power from the panels. Exactly what MPPT is supposed to do. Your PWM numbers are surprisingly good.

westbranch · March 2017

since the next step, if he stays with PWM/parallel wired panels, is he could use 3 panels. He will have to go with 4 panels if he wants to go 24V with 2 panels in series with 2 parallel strings... the benefit is that he will get less line loss, small as it will be, with the same, say 10 ga. wire or 4 in series (48V) and get even less loss... using the same wire to the CC. That is another benefit of MPPT, not to mention there should be more Amps into the depleted bank...
Low production days are another potential charging time not achievable if using an all parallel setup.

Virtuousdesires · March 2017

> @mike95490 said:
> So just for example, my 2 100 watt panels was putting out 10.5 amps at
> 13.5 volts (Around 150 watts according to the display). If I wired the
> two panels in series to make 24 volts and used an mppt charge controller
> set to 12 volts (14.6), what might those numbers look like? More
> voltage and amps going into the battery? Seems like how that works.
>
>
> Can't tell. The PWM has corrupted the the PV potential output. But taking a long shot, you have 200W @ 18V = 11A Which is pretty close to the 10.5A you currently measure. So, using poisoned numbers, and guessing wildly, you gain at least 1/2 amp, which is about full power from the panels. Exactly what MPPT is supposed to do. Your PWM numbers are surprisingly good.

Just taking the advice of a former RV blogger. Keep the controller close to the batteries and use big enough cable. I hope Sunday is sunny so I can run a voltage drop test from the panels to the controller. I already did this but didn't think to test it under load. Open circuit was just fine. From what I am gathering thus far, it appears that the voltage will drop regardless of cable size because that's how a battery does it (From what I understand from folks here and emailing a blogger).

Estragon · March 2017

The voltage will drop to battery voltage during charging, which is normal. Voltage drop in the cable depends on current (amps). Higher current = more voltage drop on a given size of wire. You can estimate the wire losses using a table like this:
https://www.solar-electric.com/wire-loss-tables.html/

Battery pulling down panel voltage???

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