Understanding Amperage

[paulhmartinez]

20+ amps going in, 8 going out yet battery drains quickly and lose all power?
Using 4x100w Poly parallel PVs into 30 amp controller charging 200 Ah gel battery to 3000 W PS inverter.
Goal is to charge an EV at 8 amps, but battery seems to run down quickly even though the amps going in is
much higher that what is being drawn.
What am I doing wrong?
Thanks
Paul

 

[MichaelK]

How are you coming up with the 20+A number? Is that based on measurements, or the panel specifications? With mis-alignment to the sun, output drops a lot. At the best of times, don't expect to get more than 85% output, and that is with an MPPT controller. If you are using a PMW controller, expect to see 60%. That's because a PWM controller drags the panel voltage down to the battery voltage.

The inverter itself is also a load, and it requires some electricity just leaving it on. Are you also factoring in the inverter as a load?

 

[Ampster]

20+ amps going in, 8 going out yet battery drains quickly and lose all power?
Using 4x100w Poly parallel PVs into 30 amp controller charging 200 Ah gel battery to 3000 W PS inverter.
Goal is to charge an EV at 8 amps, but battery seems to run down quickly even though the amps going in is
much higher that what is being drawn.
What am I doing wrong?

Amps is an instantaneous measurement. You need to accumulate Amphours, which is a time based measurement. For example you have 20 Amps going in for maybe 5 hours which is {20 times 5) 100 Amphours. Perhaps your car charges for 15 hours which is {15 times 8) 120 Amphours. There is also overhead so that not all the 100 Amphours get stored in your battery and it may need to take more than 120 Amphours out of your batteris to give your EV 120 Amphours.
NOTE: The above assumed the voltage was the same. As noted below, if voltage is different, then a more complicated calculation using Watts would help understand the issue better.

 

[acdoctor]

Amps is a measurement, like a river flowing. To calculate the gallons of water flowing in a river you would need to calculate the width and depth and speed.
Electricity is measured with voltage and amperage. One with out the other doesn’t have a lot of meaning. Voltage x amperage = wattage, and wattage by itself is a useful measurement.

100 watt panels are typically 5.5 amps at 18 volts. 4x 5.5amps is 22.2amps at 18 volts. That’s assuming you get better sun than all of the rest of us.
If you have a true mppt solar charge controller it will convert that to your battery voltage with very little loss. 22 amps x 18 volts is 400 watts. Reality is 350 watts. If you have a PWM controller it just cuts the voltage to the battery voltage.
22 amps x 14 volts is 300 watts. Reality is 250 watts.
Inverters are not 100 % efficient more like 90%. You said you are charging at 8 amps I will assume that is at 120 volts so 120 volts x 8 amps is 960 watts.
960 watts x 1.1 for the inverter losses is 1056 watts input into the inverter.
So if you only charge the car while the sun is in the best 6 hours of the day. Your solar system is lacking between 700 and 800 watts and that short fall is coming from the battery. The battery that you are not charging because you are consuming all of the electricity that is being produced. Speaking of battery’s a lead acid (gel) battery is only about 80 % efficient in a full charge discharge cycle. And of course if you want it to last more than a year you don’t want it to be drained more than 50% so 200 ah is 100 ah usable or, 100ah x 12.5 volts is 1250 watts hours of power or enough to charge the car for 1 hour with no or low solar.
Hope this helps.

 

[camelCase]

It might help to think of the system in terms of watts not amps.

The solar panels are inputting at most 400 watts of power. I bet you are charging the EV with AC current at 120v? If that's the case then you are drawing (8A X 120V) / .9 = 1067 watts from the system. The .9 in the equation is for the conversion loss of the inverter.

The reason your batteries are draining quickly is because you are drawing more than 2x the amount of power that 400 watts of solar panels can produce. Amps = volts * watts. To put it another way 400W/120W = 3.3A. (without factoring the conversion loss)

Watts vs Volts: Everything you Need to Know About Measuring Electricity

Watts, volts, amps, and ohms are common terms you will need to know when doing electrical work. Learn the difference between watts vs. volts.

www.thespruce.com

Unfortunately you need a lot bigger system to meet your goal of 8 amps of 120V AC charging.

 

[paulhmartinez]

I appreciate the input.
The panels get full sun (on clear days) for 8-10 hrs a day.
In full sun, the controller shows 20-21 amps going into the battery.
The EV level 1 (120 volt) charger draws 8 amps. I'm confused why the difference between the two, roughly 12 amps doesn't continue to charge the battery at the same time. The car (Volt) with an 18Kw battery would need about 4-5 hrs of charging. Originally, the panels were in series, but I continued to get an "over voltage" error on the controller showing 72+ volts, now in parallel it reads between 12-13 volts.
The controller is a Renogy Adventurer 30 amp. Is that a MPPT type?
The inverter is also Renogy 3000 watt, I'm not sure how much it draws.
If the 200 Amp hour battery is full, how long would I be able to draw 8 amps from it, and is it not still charging while a current is drawn? Yes, it gets completely drained to 0% each time I try to charge the car.
This is all very interesting, yet somewhat confusing at the same time.
How much bigger of a system would I need?
Thanks

 

[acdoctor]

The part you are missing is the fact that the voltage in is roughly 10 times small than the voltage out.
Take 10 minutes and study ohm’s law.

 

[Zil]

You are using 8 amperes at 120 vcolts. That needs more than 80 amperes from the 12 volt battery. You are putting 20 amperes back into the battery. Net loss.

 

[Sirtate]

The only constant measurement between the panels and the car is going to be Watts. Everything else is just units that are used to calculate Watts.

In electricity, the first calculation they teach is; Volts x Amps = Watts.
Battery storage is measured in Amp-Hours (the old way) or Watt-Hours (the new way), one is like Gallons and the other is like Litres.

So; an 18,000 Watt-Hour battery (the car batt) can store enough energy to run a 1hp motor for 24 hours (1hp = 746W), or a 168hp motor for 15mins, or 40hp for 1 hour..(the power needed at 50mph)...
Likewise at 1000 Watts charging per hour, it will take 18 hours to charge. (8 amps at 120v)

You have 400W of solar, so in order for those panels to charge the car completely, they would need to have hard sun on them for 45 hours and store that energy so it can be released into the car through the charger. (18000Wh/400w=45hours)

you have 2400Watt-Hours of Gel Cell batteries. (200Ah x 12v).
While your inverter is robust enough to power the charger, you don't have enough reserve power to keep it going long enough.

What you are doing is like trying to have a 30 minute shower with a 5 gallon water heater... It'll work at first, but get cold after a few minutes.

Things you can do;
1) increase your storage to exceed the capacity of the car, you'll need 1500 Amp hours of 12v to do so. This also requires you leaving the panels in the sun for 45 hours before you can charge. (charge on Saturdays only?)
2) increase panels to exceed 1000W and the associated amperage/voltage for the charge controller. This will allow the panels to keep up with the car charger as it's charging. (daytime use only, though)
3) do both 1 and 2.

(of course there will be losses in the system, and these numbers would likely needed to be beefed-up to work in the real world)

 

[Ampster]

My explanation earlier was perhaps too simplistic. It assumed everything was at the same voltage. Subsequent posters have updated this discussion to make it more obvious why the battery has become drained.

 

[camelCase]

120 volts * 8 amps = 960 watts

960 watts / 120 volts = 8 amps

400 watts / 120 volts = 3.3 amps


watts / volts = amps
volts * amps = watts

 

[paulhmartinez]

Thanks once again.
Getting clearer now.
More watts (panels) going in, more storage (batteries) for more reserve.
How many more 200 Ah gel batteries can I pair with this system and how many would I need? How are they then connected?
Shall I just replace my 100 watt panels with 250s? Don't believe I'd have room for more than about 2 more.
Paul

 

[krfish]

Maybe this will help: As others have tried to point out, you are using 8 amps at 120 volts. That is 960 watts (8*120).

If your inverter is running at 12 v, then you can divide that 960 watts by 12 to get the amp draw on your system.

That is a 80 amp draw... ...and is why you are killing your battery.

 

[acdoctor]

Will you expect the solar to charge the car all on its own? Or party from the grid?
How depleted will the car be daily in kilowatts?
What time of day will you be plugging the car in to charge?
This will make a huge difference on the solar batteries and panels required.

 

[Sirtate]

Thanks once again.
Getting clearer now.
More watts (panels) going in, more storage (batteries) for more reserve.
How many more 200 Ah gel batteries can I pair with this system and how many would I need? How are they then connected?
Shall I just replace my 100 watt panels with 250s? Don't believe I'd have room for more than about 2 more.
Paul

how big is your wallet? ?

In order to get enough storage to completely charge the car, you need over 18,000 Watt-Hours (the car battery is 18kWh is size)
At 12volts, that equates to 1500 Amp Hours. You have 200Ah currently. So you'd need 1300 more, so 7 would do it, if wired in parallel.
Drawing Lead acid batteries down completely isn't good for their longevity, so you would need more to provide a buffer. This is when the siren call of Lithium Ion batteries can be heard... (It's captivating, can you hear it?)
They charge faster, can be depleted fully without much detriment to their life, and can be used indoors(They don't produce hydrogen), and last multiple times longer than lead acid.

Look around these forums for Will's favourite LiPO4 batteries and shop them on those Chinese mail order sites. (they're about $2/Ah)

Panels are limited by the square footage you have to expose to the sun.
The sun shines about 1000w per square metre on the planet at noon. Solar panels are only about 20% effective at converting that into electricity. So even adding another 500w (2 of those 250w panels) ,if they'd fit, would help. You would need another MPPT charge controller to hook them up to your battery bank.
900w of solar would charge your 1500Ah lithium batteries in two days of sunshine.
Or, top up a half depleted car battery every day...

Would that work?
Otherwise, you're gonna need more panels, and you may have space issues. (see the Irradiance per metre number)

 

[paulhmartinez]

Is is possible or suggested to mix wattage of panels?
If I have a seperate controller for the 250 watt panels how would that tie to the existing one and then to the inverter?
I'm learning quite a bit here. Wish more people would consider this option.
I also ride a Zero motorcycle and cut the lawn with an Ego.
The Zero won't charge at all from the inverter, it trips the internal GFCI moments after I plug it in,
Thanks again.

 

[Ampster]

his is all very interesting, yet somewhat confusing at the same time.
How much bigger of a system would I need?

As someone said earlier, How big is your wallet? While you are contemplating that question it might be time to step back and look and some options to charging your EV in the most cost effective way. A lot of that depends on where you live, the rates your power company charge and any programs they may have for Net Energy Metering. NEM is basically using the grid as a battery. I have two EVs and have been doing that for the past ten years.
The best way to think about all of this and to put costs on it is to use kilo Watt hours. That is the unit of measure that your power company charges you and your car stores energy in kWhs. I have a grid tie solar system that if I amortize its cost over twenty years and it produces a predictable amount of energy during its life, the cost per kWh will be somewhere between 8 to 10 cents per kWh. I often charge my EVs during the day and if that is another option then we can help you figure what kind of system would be the most cost effective.

 

[Ampster]

I also ride a Zero motorcycle and cut the lawn with an Ego.

I just saw your most recent post and that opens up some possibilities for you to use some form of Grid Tie system to charge your various battery powered devices. A grid tied inverter could solve the problem of the Zero tripping the GFCI on your existing inverter. Does the Zero use a J1772 plug like the Volt?

 

[paulhmartinez]

Like most, I wish i did have a bigger wallet. I've spent a total of about $1200 so far but would consider an additional amount to make this project work.
I've had 3 estimates for whole home solar, with a battery, all were $30,000+
Not practical or worth it on a home were not sure how much longer we will be in. Maybe decades to recover that cost.
Northern IL in not really center of solar energy. Although I see it more and more, even a couple of community "farms" it is still not really an accepted method. The last of the coal plants closed in the past year locally.

 

[paulhmartinez]

The Zero DSR also only uses level one. It has a built in charger and only requires a cord to connect. That charges it's 14Kw battery from the wall plug in about 7 hrs from fully drained.
It's seldom I need full charge for the car, usually has 30 to 70% and the bike rarely needs more than half a charge.