Battery Charger

[JohnB]

Mr. Tweety

You still out there? I have been reading and reading on our charging topic. I also just got an email back from Mr. Battery.

Here is some reading on charging rates. Remember I have a Progressive Dynamics Converter so some of this is off there site. And Mr Battery refers to my setup as a PD charger for short.

http://www.progressivedyn.com/battery_manage_101.html

http://www.batteryuniversity.com/partone-13.htm

http://www.arttec.net/Solar_Mower/4_...20Charging.pdf This one is Mr. Battery recommended.

http://www.batteryfaq.org/ See the FAQ area. This one is Mr. Battery recommended.

http://www.solarnavigator.net/battery_charging.htm This one talks about the C/8 being the fastest current we should be jamming into a battery. Basically we have to deal with the heat from the higher current. If the heat gets to be too much time after time of charging we can create issues from the heat. I do have to get the C/8 rule confirmed thru Mr. Battery as we got off on to many other topics. He just bought a 5th wheel and that sort of took over the conversation….

http://www.homepower.com/article/?fi...skTheExperts_6 This guy was answering the same question on why not hit it hard while the generator is running. Heat is a problem we have to deal with.

Some more reading. This site goes further forward or back
http://www.vonwentzel.net/Battery/00...ary/index.html

Here is Peukert's Equation. I have not made it all thru this one yet. http://www.smartgauge.co.uk/peukert2.html

Here is where we are sort of coming too. I have now found this same thing in 2 places. I have to back it up with the exact why but our smart chargers are varying the voltage and current going out to the batteries. Heavier wire will change some resistance but it may not up the current if the smart charger is holding it back.


Battery Charging Voltages and Currents:

Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps. Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity. The Concorde AGM batteries are a special case - the can be charged at up the the Cx2 rate, or 200% of the capacity for the bulk charge cycle. However, since very few battery cables can take that much current, we don't recommend you try this at home. To avoid cable overheating, you should stick to C/4 or less.

Charging at 15.5 volts will give you a 100% charge on Lead-Acid batteries. Once the charging voltage reaches 2.583 volts per cell, charging should stop or be reduced to a trickle charge. Note that flooded batteries MUST bubble (gas) somewhat occasionally to insure a full charge, and to mix the electrolyte. Float voltage for Lead-Acid batteries should be about 2.15 to 2.23 volts per cell, or about 12.9-13.4 volts for a 12 volt battery. At higher temperatures (over 85 degrees F) this should be reduced to about 2.10 volts per cell.

The question comes back to, what is the limiting factor in the battery wanting to draw more current? And the 30 amp breaker Sunline put in. The charger may be limiting it on purpose.

And here is an exerpt to some of my questions to Mr. Battery. He is talking to my PD converter.


Mr. Battery Wrote:


"John, You really can’t get much better than your PD converter/charger with the microprocessor control (Charge Wizard). It is going to evaluate the battery SoC and perform the necessary charge rate automatically. All you really need to do is make sure the cells are kept full.

Deep cycle batteries are more resistant to discharge than regular car batteries. The 100% state of charge (Soc) for a battery that has been allowed to settle will be 12.650 VDC. The 50% charge will be 12.240 VDC. Most all deep cycle batteries can be discharged to 11.5 volts without damage. This is full discharged to a 0% SoC. Typical inverters (DC to AC) will work until the battery voltage drops to 11 or 10.5 VDC – way below the discharge point I consider comfortable. Thus, if you are using an inverter it is best NOT to depend on it to let you know when to turn it off.

Your PD Charger and charge Wizard will evaluate your battery based on the internal resistance of the battery and the voltage. If the resistance is high, indicating a discharged state, the PD will jack up the charge voltage enough to overcome the internal resistance of the battery. The higher voltage will cause a higher current or charge rate. As the internal resistance drops current will increase. So, the Charge Wizard lowers the charge voltage to keep the charge current from increasing. Again, it is all done automatically and you should not need to worry about it. Just watch the little green blinking light every now and then to get a feel of how it is working.

As for the wire size and the 30 amp fuse. #10 is a little on the light side, the main power cable from the PD converter to the battery should typically be #6. You can increase the wire gauge but the benefit will be minimal unless your charge current is over 30 amps and the cable distance greater than 33 feet. The 30 amp fuse at the battery sort of throws me. That is not typical for a converter/battery charge circuit. Are you sure that 30 amp fuse is not for the electric tongue jack?

I don’t know if I have helped or confused you more. Feel free to ask questions again. BTW, it is resistance not impedance that you should be concerned about in your cable.

The group 27 battery will give you more amp hours than a group 24. Most deep cycle batteries are rated at the 20 hour discharge rate but a few use the 10 hour rate. If you are looking at Ah to compare batteries, make sure that the same discharge rate is also used. Here is another web site to read and play with the provided calculator to see what you might expect from different Ah battery ratings like the twin group 27’s or two six volt golf cart batteries.

http://www.gizmology.net/batteries.htm

Bottom line, whatever you “think” you have in capacity, divide it in half for a realistic figure to depend on."

More yet to come as my curiosity is still not cured. Something is holding the battery back from taking more current and it may be the changer, not the wire size. And I need to clarify a few things with Mr Battery. The Sunline 30 amp breaker seems unusual to him. He stated no 10 waire and that was a mix up. I know mine is either an 8 or a 6.

Did you find anything more?

John

[Mr Tweety]

John,

WOW - Mr Battery certainly deserves his title. Plowed through the websites - all great. Some comments, observations:

1. The converter to battery cable in my Sunline is AWG 6. I suspect this is common. According to current ratings for less than about 0.5 volt drop over 15 feet or so (my set-up) this is capable of 30 amps. Mr Battery agrees with the 30 amp @ AWG 6. For AC voltage this wire could carry much more since we are dealing with 120 - 220 volts and who cares about a few volts. But for DC 12 volts - we know that even a half volt loss can dramatically affect charge current. Per Mr battery - the difference between a fully charged battery at rest (12.6v) and a depleted battery (about 11.9v) is less than a VOLT !!!!!

2. Regarding the mysterious 30 amp fuse:
First - even Mr Battery thinks this is strange. The charge wizard is reading the voltage and resistance of the battery to compute the correct voltage and thus current to apply. It would only attempt to apply it's advertised 50 - 60 + amp capability ( 14.5 volts +) if it sensed a completely depleted battery. And that current would assume a battery in good condition with a relatively low internal resistance and better than AWG 6 wire with less than 0.2 volt loss or so at that amperage over the length.

But I think the big factor here is this : NONE of us really discharge our batteries that far !!!!! We don't like to do this - our chargers are plugged in all the time and don't allow it --and we don't boondock enough to create the situation. The real test here is to deplete the battery to a rest voltage of 11.9 volts or less. Then let your charge wizard "do it's thing" and measure the amperage at bulk rate using your fancy fluke-meter. You may need to upgrade the wire beyond AWG 6 to really get the 50 + amp rate.

3. I note that Mr Battery - or one of his sites - recommends assuming a working Amp hour of about half of what the total advertised Ah is for the batteries. I have seen that elsewhere and it makes sense.

4. I will attenpt to measure my charge current using the "shunt" method suggested in an earlier post by one of our contributors. I made one per instructions from his reference. I will report this at next boondock session which may not be till this fall !!!!

Thanks for all the info. !!!!!!

Mr. Tweety

[JohnB]

Steve

There is still one thing missing. What is the charge algorithm of your converter? Does it subscribe to the C/8 method of max current rate? If it does it is only going to put out that much current even if it has a no. 00 awg wire. Sunline set these things up with that 30 amp breaker in there a long time now. And my battery tray from Sunline will only accpet 2 grp 24's until I made it bigger. So there was fixed max ah capacity in the entire design. We are missing something. Sounds like some real good camp fire talk us “types” of curious minds.

Here is my latest typing to Mr. Battery. He is tied up and has not got back to me yet.

See if you can follow this thought process. I explain to him my quandary.

Dear Mr. Battery

Now to my battery charging. What I’m after is

What is the max allowed (recommended) charging rate in amps? I’m assuming the voltage is up at 14.4 in the high amp bulk mode. I have read about C/8 for lead acid wet cells as being the recommended limit. And if I under stand this right….please straighten me out if not, If I have a group 27, 115 AH battery rated on 20 hours, then this is 115/8 = 14.4 amps max current recommend. Did I get this right and is the C/8 right?

Here is a cut and paste. See mid page. http://www.solarnavigator.net/battery_charging.htm

Battery Charging Voltages and Currents:

Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps. Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity. The Concorde AGM batteries are a special case - the can be charged at up the the Cx4 rate, or 400% of the capacity for the bulk charge cycle. However, since very few battery cables can take that much current, we don't recommend you try this at home. To avoid cable overheating, you should stick to C/4 or less.

Charging at 15.5 volts will give you a 100% charge on Lead-Acid batteries. Once the charging voltage reaches 2.583 volts per cell, charging should stop or be reduced to a trickle charge. Note that flooded batteries MUST bubble (gas) somewhat to insure a full charge, and to mix the electrolyte. Float voltage for Lead-Acid batteries should be about 2.15 to 2.23 volts per cell, or about 12.9-13.4 volts for a 12 volt battery. At higher temperatures (over 85 degrees F) this should be reduced to about 2.10 volts per cell.

I have found this in a few places. Is this correct? I’m assuming heat is the enemy here?
I’m trying to learn/understand what is going on in the battery to not want to go above that current as a constant practice.

And I’m trying to figure out if I discharge my batteries down to no less then 50% how long will it take running the genny to get then back to at least 90%? Then when it kicks down to 13.6volts how long until 95%? Can I just do something up to the 90 to 92% area?

Trying to find the math on how to recharge. If C/8 is the number the PD uses, then it is limiting the current, not the battery being able to take it? I guess that is the question. What is limiting the current, the battery being able to take it or the charger putting it out?

So let me see here…tell me where I go wrong. Charging at C/8, or 115ah/ 8 =14.375 amps into a 115 ah battery that is at 50% SoC to 90% (is 90% 103.5 ah?)

Does it go like this: 115*.50 = 57.5 ah at 50%. So 50 to 103.5% is 46 ah’s to charge back in. And if I’m putting in 14.375 amps/hour charge rate it this 46/14.375 = 3.2 hours? Is it this simple?

Now if I actually did that right, what I do not know is what the PD charging algorithm is. Does it detect my battery and only put out 14.375 amps or less or more? If so then up’ing the wire big time is not going to really help. But if I put 2 batteries on then that current would double would it not? Would try and pass 28.75 amps.

Which if I did that right then that 30 amp circuit breaker is getting real close.

See here for my original converter hook from American Enterprises and Sunline



This is the confusing part. Here at the power center, if nothing is running in the camper then the wire and the fuses here can pass 60amps. Yet the 30 amp breaker in the TT tongue will not let it.

Is the charger smart enough to sense the battery changing resistance and only put out 14.4amps to the bus if I was at 50% Soc?

And if I turn on 5 lights in the camper and some other things the draw say a full 30 amps, the converter boosts the current to 48.4 amps? 30 amps is being consumed in the TT, 14.4 going to the battery? And then If I shut down the 12 volt coffee pot say, ( I don’t have one but just talking) Then the converter regulates back the current automatically?

Tell me if I get this right:
Basically the converter is an amp regulator along with a volt regulator. It is smart enough to sense a battery resistance to DC common and regulate an amp and volt value to charge the battery. It sends that amps out into the DC buss and connects to the battery. On top of this it can sort out other loads on the DC buss and boost the current to compensate up and down. Some how it knows what a battery resistance is compared to a Maxx air fan or 12 volt light bulb. (how does it do that?)

And some how if a battery goes way down in Soc, it will not pass any more then C/8. It somehow knows the resistance of total ah capacity hooked to the buss? It can sort out 1 or 2 Grp 24 or 27’s on the line.

OK what did I say right or wrong?

See pics of charge setup on the PD tie in







More when I get a response. And we can point and talk on the weekend.

John