Battery charging with intermittant power source

The first method - a 3 stage "smart" charger. That assumes you have done your research and worked out your energy budget and can obtain a smart charger that meets your requirements and will use batteries of the proper type, size and number and ...... I'm guessing you haven't done all of that.

Ed

(a) Attend to what Ed said.

(b) Are you thinking of flooded cells, SLA/VRLA or ... ?

(c) Why do you think your "cycle charging" approach is compromised by the intermittent source?

Lead acid batteries are best charged with a constant voltage source. Charge current depends on the state of the charge of the battery. It works similar in a car.

Jan

This is true, but the voltage source must be current limited. This amounts to a current source into a completely discharged battery, changing over to a voltage source as the battery charges. It works similar in a car. ;-)

Most alternators go "balls-to-the-wall"... 50A-60A ;-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

Even a basic plug-in charger will do in the neighborhood of 10A, limited only by its parts . What can your solar or wind system supply?

----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----

The #1 Newsgroup Service in the World! >100,000 Newsgroups

---= - Total Privacy via Encryption =---

is

Any particular reason why you just don't buy a charge controller?

For an intermittent source, you need to insure your load is serviced by undervoltage lockout hardware. I bought some surplus NEMA box basically for the box, i.e. not what is inside. However, the box contents were instructional since I've never built this kind of outdoor gear for a living. The box had a DSC LBCM. DSC is the company, Digital Security Controls. LBCM stands for Low Battery Cutoff Module. I haven't tracked down a manual, though the thing is just a relay and a dozen discretes on a two layer board. Certainly reverse engineerable. Presumably they limit the battery to a minimum of 10V.

this

Charging lead acid should be based also on _temperature_:

Refer to my patents...

3,496,447 Alternator Voltage Regulator Responsive to Temperature 3,505,590 Temperature Responsive Output Voltage Apparatus 3,522,482 Temperature Compensated Voltage Regulation 3,546,563 Alternator Voltage Regulation Utilizing A Constant Current Source

(Copies in PDF format on my website, near bottom of home page)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

But it's a current source. ;-)

Constant voltage source and a discharged battery can mean quite huge intial charge current. In ALL types there needs to be SOME mechanism for limiting current into the battery. Whether this is intrinsic in the charger (which it often is) defines the need to provide a specific limiting mechanism.

For SLA types, simple CV charging is NOT the regime of choice. A worthwhile read on care and feeding of SLA's can be found in Unitrode (now TI) app note U-104 (search for SLUA115.pdf).

I'm still waiting to see the O/P's responses to (b) and (c) above.

Yup. Alternators are not voltage sources.

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food

(b) I am dealing with SLA at the moment, but I am interested in learning about VRLA as well.

(c) according to this site:

The stage 2: "constant voltage" is required for a fixed time (assuming you are charging a battery from a discharged state) for optimal battery life. I cannot guarantee that 1. the battery is discharged when the regulator powers up and 2. That the power will be on for the fixed time. Using a fixed time is not practical, unless another termination condition (such as temperature, or current) is used.

To provide a few more details, I am working with a 3.6kW power supply with both programmable voltage regulation and programmable current limiting. Obviously the 3.6kW number is not guaranteed, depending on wind or solar conditions, so the current limit may not even come into effect, and the supply may not be able to reach the desired voltage either. I am looking for the method that will cause the least damage to the batteries using this type of supply.

Scott

first you need to decide how much energy you can afford to waste.

rom

r

is

at

ng

age

n this

ry.

by the

tial

miting

which it

thwhile

note

m o

It certainly helps that you gave this some scale. I assume you are charging a stack of batteries.

On a sunny day (Fri, 9 Jan 2009 17:19:12 -0800 (PST)) it happened " snipped-for-privacy@sushi.com" wrote in :

Exactly. I just did one, there is a flashing alarm when the battery drops below 10.7 V, and a switch off, using power MOSFET, when 10.0 V is reached, also with alarm. There is current limit and voltage limit on the charger. There also a a time limit on the charge (24 h for sealed lead acids). Also the Ah hours is calculated from the current. I guess I could make some assumptions, and limit charge on Ah hours too, but then would need to monitor temp as well. You can get as sophisticated as you want with a PIC :-)

You want to limit the charging current to the lead acid battery. In the wind or solar power case, this can be taken care of by the design of the power source.

There are chargers that purposely pulse the current into the battery. You may want to read up on this.

When the battery nears the fully charged state, you want to drop the charging current down to a smaller value. This is usually done by holding the voltage at the "charging" voltage for several minutes.

Once the battery is fully charged, you only want to feed a current into it that is equal to its internal leakage. More current than that tends to boil away the water.

Your circuit needs to remember where in the charging process you are when the power goes away. I'd suggest using something like a supercap to hold the power up. This way, it can check the state of things every second or so to see if you have taken power from the battery while the sun was down.

is

.7 V,

larm.

Before I start any home project, I carefully search the commercial market. Not often is it cheaper to DIY unless your time is free. I generally build it myself when the price savings is large or I can achieve better specs.

I want to set up some gel cell charging scheme where the 3rd row of my SUV resides when folded. [That is, yank out the seat and have a shop build a lid, then recover the space for electronics.] There are plenty of battery isolators on the market, but most charge controllers from the solar and wind market can't handle the low drop out of being charged from an alternator. However, the Blue Sky products look promising:

The trick with all these chargers is to interpret their nebulous datasheets.

On a sunny day (Sat, 10 Jan 2009 14:51:34 -0800 (PST)) it happened " snipped-for-privacy@sushi.com" wrote in :

Yes, sure, never design or build something you can buy for a fraction of the price. That is often the case with things like amplifiers, TV's, NiMH chargers, what not. Still it may be fun.

Anyways, I just took the gel battery specs, it told me the max charge current, charge time, charge voltage, and a lot of other interesting stuff. I already had the power MOSFET switch part (you cannot buy that), the PIC with plenty of analog inputs, so on suggestion of somebody here, I used the voltage drop over the MOSFET to measure current (it is almost exactly 20 milli Ohm). And the rest is just basic math in the same PIC (that also drives a 4 line text LCD display). I dunno total cost, but I think I can match that 600 $ price tag on

This gel battery has now had about 1200 full charge / discharge cycles, with very little decrease in performance I can see, so I must be doing something right, If something does not work, then I can fix it, an other advantage of DIY. And in this project, using proto board, the design was practically rebuild 2 times.. If I have some idea I can just try it out, added a second PIC a few weeks ago. It has remote control from the PC via RS232, and manual control too. I can read battery status from anywhere in the world, and control it too. (It powers an amateur radio transmitter). I can even make it play audio files from anywhere in the world, as the audio comes via the PC, digital processor. Or have the receiver record something.... Also on a timer (using crontab). Now that is something you cannot buy anywhere...

You want to run that car on gel batteries? Or just use the car to charge those?