# Solar charging questions

#### fixit7

Joined Jun 2, 2019
11
I have a solar charger I am using with my car battery.

The current voltage of the battery is 12.7 volts.

And the charger is still charging.

Here are some specs for the charger.

Rated power output = 5W
Operating power voltage = 18V
Operating power current = .33A
Trickle charging current = .2A
Floating charging Voltage = 13.8
Overcharge Protection Voltage = 14.1 Voltage

At what battery voltage will my solar charging stop?

Thanks,
Andy

#### Yaakov

Joined Jan 27, 2019
3,765
"Floating charging Voltage = 13.8"

Lead chemistry batteries are "floated", that is, continuously trickle charged at 13.6-13.8V. The chemistry permits this, and it keeps the battery fully charged.

Here is the premier source for battery charging information: https://batteryuniversity.com/article/bu-403-charging-lead-acid

#### fixit7

Joined Jun 2, 2019
11
I think you are referring to the car charging system not what the solar charger is doing.

I am using the solar charger because of a device in my car that uses a lot of current.

The alternator is not able to keep up, thus the use of the solar charger.

I was hoping the specs I listed would tell at which voltage my solar charging would stop charging at.

Would Overcharge Protection Voltage be what I am looking for?

#### Ian0

Joined Aug 7, 2020
3,784
Don't leave a wet-cell car battery on float charge. Unless you remember to top up the water regularly, you'll ruin it. The continuous over-charge electrolyses water. In a flooded battery, the water is lost, but in a VRLA battery it recombines.

#### Ian0

Joined Aug 7, 2020
3,784
I am using the solar charger because of a device in my car that uses a lot of current.
The alternator is not able to keep up, thus the use of the solar charger.
The alternator can provide perhaps 50 Amps. The solar charger can provide 0.33A.
If 50A isn't enough, I can't see the extra 0.33A making the slightest bit of difference.
I was hoping the specs I listed would tell at which voltage my solar charging would stop charging at.
Overcharge Protection Voltage = 14.1V.
But it will never get there if there is a load >0.33A

#### fixit7

Joined Jun 2, 2019
11
The alternator can provide perhaps 50 Amps. The solar charger can provide 0.33A.
If 50A isn't enough, I can't see the extra 0.33A making the slightest bit of difference.

Overcharge Protection Voltage = 14.1V.
But it will never get there if there is a load >0.33A
Thanks.

I understand. Can I determine the current draw by disconnecting the positive cable?

My meter has a 10 amp setting.

#### Ian0

Joined Aug 7, 2020
3,784
I understand. Can I determine the current draw by disconnecting the positive cable?
My meter has a 10 amp setting.
Yes, you can, but not if the inrush when you reconnect it blows the fuse in the meter!

If you have a mV setting, then maybe there is a length of cable that you can measure the voltage drop across.

#### fixit7

Joined Jun 2, 2019
11
Yes, you can, but not if the inrush when you reconnect it blows the fuse in the meter!

If you have a mV setting, then maybe there is a length of cable that you can measure the voltage drop across.

What is an inrush?

I have a 200 mV setting.

#### LowQCab

Joined Nov 6, 2012
1,372
"" The alternator is not able to keep up, thus the use of the solar charger. ""
A Solar-Panel is not a "fix" for an inadequate Alternator.
You'll just trash your Battery by running it very low on Charge repeatedly.

Get a bigger Alternator,
(but keep the Solar-Panel, it's good for Battery-Life).
.
.
.

#### Ian0

Joined Aug 7, 2020
3,784
What is an inrush?
The large load will probably have some parallel capacitance, or be a motor that has to start up from rest.
The "inrush" is the current that rushes in either to charge the capacitance or to get the motor up to speed.

#### Tonyr1084

Joined Sep 24, 2015
6,465
Better than just leaving us to guess what you're working with, tell us exactly what the circumstances are. I've gotten the impression you want to charge the car battery while you are not using the equipment so that the battery is fully charged when you do. It doesn't sound to me like you expect 330 milliwatts to make up the difference your equipment uses, it sounds more to me like you want to keep your battery as charged as possible.

Float charge is the charge that you keep your battery at when being charged. It does a number of things; first, it prevents sulfides from building up on the plates of the battery. It also keeps the battery fully charged. However, a truly fully charged battery - when NOT on any charging system, and given hours to rest, should be 12.6 volts. Nominal voltage is 12 volts, that just refers to the battery type. This case it's a 12 volt battery. 12.6 volts is the voltage I want to see on my car batteries first thing in the morning, before the engine is started.

So we don't know what amperage your alternator is capable of; but if we assume it's 50 amps, what equipment are you running that draws more than that? A stereo system with a really big amplifier? That's where I put my money - on an amplifier. If so - and I know they DO make some hellacious amplifiers, you may need a bigger alternator. They sell them well over 100 amps. I want to say 160 amps, but I'm not into that world and don't know that for sure. If you are not running such heavy equipment then there may be another cause for battery voltage drop-off. You could have a slipping belt. The alternator belt might not be tight enough. You may have a bad tensioner. There are just so many possibilities.

Start with giving us all the information you can on the battery size (not just 12 volts, the Amp Hour rating (AH) is important too). Is this IN your car? What's the equipment you are trying to run? What limitations are we to understand? Money? Space? Time? There are a lot of really smart people here who can guide you through successfully, but they're going to need more information.