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Trickle Charge idea for Winter.

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Re: Trickle Charge idea for Winter.

Post by RickHaleParker » Sat Jan 13, 2018 11:02 pm

The Buck converter solution does work. I came up with it for a guy that wanted to maintain the batteries in his boat but did not want to spend the money for a full Solar Charge Controller. It works and works well for maintaining a battery that sits for long periods of time. He paid 79¢ for a 3A Buck Step Down Module off eBay.


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Re: Trickle Charge idea for Winter.

Post by RickHaleParker » Sun Jan 14, 2018 8:10 pm

If someone does all that work, they my as well start selling them... There is more than a handful of folks that could likely use them.

Hum ... wheels turning .. My retired sister sews things and retails them for extra income. Would be a matter of working out the engineering, would it be better to go after universal, which often looks tacky, or custom fit.


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Re: Trickle Charge idea for Winter.

Post by wizechatmgr » Sun Jan 14, 2018 9:39 pm

Custom fit - of course :)


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Re: Trickle Charge idea for Winter.

Post by MrAl » Mon Jan 15, 2018 10:44 am

RickHaleParker wrote:
Sat Jan 13, 2018 11:02 pm
The Buck converter solution does work. I came up with it for a guy that wanted to maintain the batteries in his boat but did not want to spend the money for a full Solar Charge Controller. It works and works well for maintaining a battery that sits for long periods of time. He paid 79¢ for a 3A Buck Step Down Module off eBay.
Hi,

A buck converter converts a higher voltage into a lower voltage but with increased current. That can mean getting more power to a 12v battery from say a 20v solar panel. The buck converter is a "true" power converter because it converts power not just voltage or current alone, which means efficiency often (but not always) goes up. The overall efficiency depends on several factors including input/output ratio.

There's another factor that enters into the picture though with solar panels. That is, the point where we get maximum power out of the panel. The max power point (MPP) of the array is the point where the product of voltage times current is at a maximum, and that point is reached with a circuit that can actually find this point and make use of it.

Since the buck converter is a true power converter, that means if we put in the maximum power we get the maximum output power. To get the maximum power input though we need a max power tracker circuit as well as a buck, or just a circuit that combines both. These circuits should be able to be found on the web or build one yourself if you are into that kind of thing, as many people do this as a hobby these days.

This is of course if you dont mind a little extra complexity to get the maximum energy you possibly can from the panel. Of course you also dont want to fry the battery :=)

To find out more you can search online or go to sites like All About Circuits for example. There are a lot of people there who know about these circuits and how to get one or build one or even design one.

Good luck with your project.


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Re: Trickle Charge idea for Winter.

Post by RickHaleParker » Mon Jan 15, 2018 11:31 am

The buck converter is a "true" power converter because it converts power not just voltage or current alone,

Technically there is no such thing as a power converter. Power is not a quantity it is a rate. Specify power is the rate energy is transferred or converted to another form of energy. You can use different units for power but that does not change the rate.

A buck converter is a DC-DC voltage converter. The current will change with the Voltage to comply with Power = Voltage * Current but input power and output power will always be equal, some of the output energy will be in the form of thermal energy rather then electrical energy but thermal energy is still output energy and it counts.

One could add programing to seek out the Maximum Power Point of the solar panel. That is exactly what a MPPT Solar Charge Controller is. A Buck Converter with programming to seek out the solar panels MPP. A MPPT is overkill for this application because all this application needs is float chargeing to maintain the battery charge not charge the battery from a state of discharge. If one matches up the Buck Converter with the Solar panels, one can do this application with a 79¢ buck converter, a full blown MPPT Solar Charge Controller is not needed.


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Re: Trickle Charge idea for Winter.

Post by MrAl » Mon Jan 15, 2018 5:01 pm

RickHaleParker wrote:
Mon Jan 15, 2018 11:31 am
The buck converter is a "true" power converter because it converts power not just voltage or current alone,

Technically there is no such thing as a power converter. Power is not a quantity it is a rate. Specify power is the rate energy is transferred or converted to another form of energy. You can use different units for power but that does not change the rate.

A buck converter is a DC-DC voltage converter. The current will change with the Voltage to comply with Power = Voltage * Current but input power and output power will always be equal, some of the output energy will be in the form of thermal energy rather then electrical energy but thermal energy is still output energy and it counts.

One could add programing to seek out the Maximum Power Point of the solar panel. That is exactly what a MPPT Solar Charge Controller is. A Buck Converter with programming to seek out the solar panels MPP. A MPPT is overkill for this application because all this application needs is float chargeing to maintain the battery charge not charge the battery from a state of discharge. If one matches up the Buck Converter with the Solar panels, one can do this application with a 79¢ buck converter, a full blown MPPT Solar Charge Controller is not needed.

Hello there,


I am not quite sure what you are tying to say here. Are you challenging me to an engineering bro-down or did you just mis speak a little there? If the former then i havent had my beer yet but im working on it because i will need it right after this post :-)

Seriously though, if you are going to challenge someones technical info who has worked in the power conversion industry (note the phrase "power conversion") for many years and other electronic industries since the early 1970's then you darn well better know what you are talking about. Sorry to say, something is wrong here.

First we see you have the unusual idea that power is not a quantity. I dont think i have ever heard anyone say that before, that i remember anyway. That includes engineers from all over the world, including professors and grad students from universities like MIT, Perdue, and Rutgers. I really cant see how you could have gotten that idea.

Second, the phrase "power conversion" is an accepted phrase for when a converter can actually convert energy from one from to another, which differs from when just a voltage is changed for example (usually lowered with a linear regulator).
There is even a formula for the efficiency based on power.

Power is a word that is used in this context to mean energy, but that's an accepted convention and is used more commonly then "energy conversion" mostly because power conversion usually refers to electrical energy conversion when "energy conversion" could mean any type of energy conversion not limited to electrical energy.

The buck is referred to as a "true power converter" because it takes in one form of power (or energy) and puts out another form. So we have in the ideal case:
Vin*Iin=Vout*Iout

or in short:
Pin=Pout

and that is exactly how it is written in many text sources.

When efficiency is involved we see:
Pout=Pin*Eff

where Eff is expressed as a decimal percentage like 0.60 for example.
What we usually dont see (although there is nothing wrong with this) is:
Wout=Win*Eff

where W is the energy. That's acceptable, but the P form is more common.

The main difference where we might see the two different forms is we probably more often see the W form in physics books while the P form would appear more in electrical books.

Now if you'd like to call the buck a "true energy converter" that's fine with me, but you cant really say that it is not a power converter without stepping on some toes :-)

Just curious what you've studied in the past. I ask because i have never heard anyone state that power is not a quantity.
The difference between a quantity and a quality is that a quantity can be stated with a specific number while a quality is a very broad definition of something. A quantity can be a rate also, which is like mpg (miles per gallon). If we say that we get "good" gas mileage that is qualitative, but if we state that we get 22.5 miles per gallon that is quantitative. That is a rate also and of course is a quantity, and that differs from say 33.2 mpg of course which is a different quantity.

I am always open to further argument on either side, but in this case i dont see much elbow room.

As a side note, i dont think it is an overkill unless you dont need it with your specific panel and general installation. An overkill is something that is not needed, and we can not decide that without knowing the specific installation and operating conditions.


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Re: Trickle Charge idea for Winter.

Post by RickHaleParker » Mon Jan 15, 2018 6:07 pm

"First we see you have the unusual idea that power is not a quantity."

Is a fact power is a rate not a quantity This is fundamental, whip out your training manual and read the definition for power, not the equation, the definition. Or you can just google "Power Scientific Definition".

"then you darn well better know what you are talking about. Sorry to say, something is wrong here."

I know what I'm talking about and can back it up.

"Sorry to say, something is wrong here."

You spent time in the energy sector and engineering and you don't know power is a rate not a quantity ... that is whats wrong. People reading this are going to Google "Power Scientific Definition" and get the facts.

"I really cant see how you could have gotten that idea."

I did something different when I was in school, I got educated instead of just learning to pass a test.

"Second, the phrase "power conversion" is an accepted phrase"

Common mis-usage like Volts = Current * Resistance instead of Electromotive Force = Current * Resistance.
Electromotive Force, Current and Resistance are quantities. Volts, Amps and Ohms are units of measurements.

"where W is the energy. That's acceptable, but the P form is more common."

Watts is not energy, Watts is the unit of measurement for Power. A Coulomb, Joule or Killowatt-hour is energy.

"Now if you'd like to call the buck a "true energy converter" that's fine with me"

I never call it an energy converter. I called it what it is, a voltage converter. Besides it is electrical energy in, electrical energy out with a little unintentional energy conversion to thermal energy. Negligible because Buck converters are typically better the 98% efficient.

"The buck is referred to as a "true power converter" because it takes in one form of power (or energy) and puts out another form. So we have in the ideal case:"

One cannot change the form of power, there is only one kind. Energy a different story, there are many forms of energy.

"The difference between a quantity and a quality is that a quantity can be stated with a specific number while a quality is a very broad definition of something."

I did not use the word "quality", I used "quantity".

Energy is a quantity, Electrical Energy can be stated in Coulombs, Joules or Killowatt-hours.
Watt, the unit for Power is One Coulomb of energy per second or one Joule of energy per second, both are quantity/time the equation for rate.

"I am always open to further argument on either side, but in this case i dont see much elbow room."

Are you one of them ... Facts don't matter, your right?


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Re: Trickle Charge idea for Winter.

Post by mecheng » Tue Jan 16, 2018 6:42 am

Wow quite contentious, ok here is a technical question to keep the peace:

I noticed the solar panel puts out 18-20V (measured with a multi-meter), but the current is only 20mA. I'm not surprised about the low current as it wasn't a perfectly sunny day, and the 2.5W rating is for ideal conditions but I was surprised about the high voltage.

I assume with the small current it shouldn't damage the battery? I know typically trickle charges work at ~13-14V but apparently the solar charges use higher voltage. Thoughts


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Re: Trickle Charge idea for Winter.

Post by abscate » Tue Jan 16, 2018 9:06 am

Yeah, we don't really do that here on MVS. Once the dust settles, Ill take this back to a reference thread


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Re: Trickle Charge idea for Winter.

Post by MrAl » Tue Jan 16, 2018 9:18 am

mecheng wrote:
Tue Jan 16, 2018 6:42 am
Wow quite contentious, ok here is a technical question to keep the peace:

I noticed the solar panel puts out 18-20V (measured with a multi-meter), but the current is only 20mA. I'm not surprised about the low current as it wasn't a perfectly sunny day, and the 2.5W rating is for ideal conditions but I was surprised about the high voltage.

I assume with the small current it shouldn't damage the battery? I know typically trickle charges work at ~13-14V but apparently the solar charges use higher voltage. Thoughts

Hi,

Thanks for your gracious reply :-)

For a car battery i would have to question the effectiveness of a 20ma curernt charge. To compare to a small 12v NiCd or NiMH cell, 100ma is the minimum charge although 50ma is sometimes used, and that is for a 2000mAHr rated cell. A car battery is 25 times that as a minimum, or something like 50000mAHr, which would be almost like 25 AA size NiMH cells in parallel.

We get into a factor known as charge acceptance. A battery accepts charge at a certain rate and this goes down with current level because of various reasons. Once we get down to a ceratain level, there is no longer any charge taking place because the current all goes into supplying the self discharge of the battery. For example, if the self discharge equates to a current drain of 20ma per day, then 20ma charge current to the battery will jnot charge it, but it will 'maintain' it at the current level. Since this changes so much though with temperature it's hard to nail down the exact value, so it could be 21ma, 22ma, and if so, then the battery is still discharging although at a slower rate than before we supplied the 20ma charge current. So getting the current exactly right is hard to do anyway. You either err on the high side or the low side.
Some experimentation could help here though. Just monitor the battery voltage before starting the vehical and see if the voltage went up or down. If it goes down, it was discharging. If it goes up, it was charging.

So 20ma does not sound like enough, but it could help a little so it might be work a try. Better would be 100ma or maybe even higher. 200ma is a typical rate for 2000mAHr 1.2v AA size NiMH cells for example, but that is considered a low to medium charge rate.

Modern 12v lead acid battery chargers have a 3 stage charge regimen.

Oh BTW, if the panel puts out 20v when you connect it to the 12v battery it will assume the voltage of the battery or else it is not connected properly or it has a controller of some type. There is probably a series diode too though that drops about 0.7 volts.


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