battery charge

[TQ60]

Charging current depends on a few things but main one is state of charge followed by condition or internal resistance of the battery.

A good battery with say only 10 minutes if inverter use could easily draw more than C rate for a short period of time.

So a 100 amp hour battery could easily draw 100 amps charge current if the charger had it in it.

That current would drop down as the battery is charged.

One should always read the battery spec sheet for what the battery is expected to do and how to treat it.

Once the battery come up a bit the current may drop to 20 or 30 amps per string.

Once fully charged and floating the charge current should not exceed 0.1% C do that example 100 AH battery that was taking 100 amps at first should only get 0.1 amp of charge current.

This is controlled by charging voltage so it needs to be set correctly.

Another note is the battery that has been under load for some time but does not draw a good charge current may be of higher internal resistance and weak if the current is not being limited by bad connections or charger settings or condition.

For more information please search battery charging maintenance and troubleshooting for about a weeks worth of reading.

[BatteryPro]

Originally Posted by FixerCQI

... I have (what I believe to be) 4 UL16HC 6V LLA (420AH for 2 batteries, so 840AH for 4??) connected ser./par. 4 batteries for residential fridge option.
I read where you said the current, during charging, should be no more than 13% of the C20 rate. Am I calculating correctly to find that my charge rate could be 4X30a=120a? That is about what my charger shows, but I thought that it was quite high.Bob

Hi Bob,

The 13% is a specification from Trojan battery. Your battery (I think) was distributed by Interstate. They may have different charge parameters so I would check with them to see what you can use.

If you use the 13% rule, then simply multiply the AH total capacity at the C20 rate and multiply by 13%. 840 times 13% is 109 amps. Voltage does not matter in this equasion.

Larry

[Old Bounder]

Originally Posted by FixerCQI

Hello Battery Pro, Larry if I may; Hope your still following this thread. I have (what I believe to be) 4 UL16HC 6V LLA (420AH for 2 batteries, so 840AH for 4??) connected ser./par. 4 batteries for residential fridge option.
I read where you said the current, during charging, should be no more than 13% of the C20 rate. Am I calculating correctly to find that my charge rate could be 4X30a=120a? That is about what my charger shows, but I thought that it was quite high.Bob

OOOPS! my bad...

[FixerCQI]

Thank you all, gents, for the information. BatteryPro, you are correct, I have Interstate batts. I will try to get some info from their site.
There is a thermal-couple on one of the terminals that seems to limit the current here in Florida. It's 95* here today. The last time I charged was in Canada and it was about 50* and drew about 127a till it settled down to 110 or so. In Florida it starts out at maybe 120a and soon it's down to 87a. I expect it is regulating by temperature at the battery.
Can you answer one other question? How low should the batt. V go before you recharge it, or would you just leave the charger on it. The charger seems quite sophisticated. It goes through 3 or 4 phases of charging, and eventually stops charging. If I understand correctly it is best to cycle LLA batts but if left on the charger I don't think the Voltage gets down very far before the charger cuts in again.

[FixerCQI]

Seek and ye shall find I picked this up from another fellow who had just ask about the same batt. I would think that taking 80% of the charge off them is a little drastic though.


Re: Interstate battery charge specs?




To follow are our recommendations for maximizing the life of deep-cycle batteries.

( 1 ) The batteries will last longer (more charge and discharge cycles) if you recharge them at the end of each day that you use them. The batteries should not be discharged below 20% of the total capacity (or 1.8 volts per cell) during normal operation (that is, there should be at least 20% of the total capacity LEFT in the battery),

( 2 ) water used must be distilled water

( 3 ) batteries should be watered after charge (unless plates are above water level prior to charge). Water level shall be kept 1/4" below the bottom of the fill tubes that go down into the each battery,

( 4 ) battery charger should be designed specifically for the battery application,

( 5 ) the charging practice should enable batteries to cool before usage.

Cordially,
Dan Lane
Customer Service
Interstate Battery System of America, Inc.

[BatteryPro]

You are right about some things. Here’s a few corrections and observations to help other readers:

Originally Posted by TQ60

...A good battery with say only 10 minutes if inverter use could easily draw more than C rate for a short period of time….

So a 100 amp hour battery could easily draw 100 amps charge current if the charger had it in it…..

“C” refers to capacity. If you have a 400AH battery (the C20 rating) your statement suggests that it could draw 400 amps. The current a battery absorbs is always controlled by the battery circuit resistance, which includes the battery resistance, up to the capability of the charger. If I provide unlimited current and voltage, the current flowing in a battery circuit will self limit by the electrochemical reaction of the battery.

Some batteries, such as AGM, have a much faster reaction time and less internal resistance so they can absorb more current that a flooded battery, which is relatively inefficient. It is unlikely that any 100AH flooded battery can absorb 100 amps of current.

Originally Posted by TQ60

...Once fully charged and floating the charge current should not exceed 0.1% C do that example 100 AH battery that was taking 100 amps at first should only get 0.1 amp of charge current. This is controlled by charging voltage so it needs to be set correctly….

Battery current is not controlled by voltage in your example. As in my explanation above, it is the battery circuit resistance that controls the current. Lead acid battery chargers are Constant Current/Constant Voltage (CC/CV). Once the battery plates become saturated and terminal voltage becomes equal to the charger voltage, the current will decrease as the chemical process is slowing down. The charger current is still available but the battery can’t use it.

Once a battery becomes fully saturated, the current will become relatively stable. The battery still has resistance which is why a small current still flows. This “float” current is not dependent on voltage. New batteries have a high resistance and require more current, and, as the battery ages internal resistance increases requiring more current to maintain the constant absorb or float voltage.

In my battery business, I am often asked why a charger will not put out more current when it has the ability. The answer is that battery current is always controlled by the battery when using a CC/CV charger.

Larry

[Gerryl]

Wow, The info here on this thread is making my head spin. Way too deep for my small brain to digest. But I have a simple question for the battery experts on this thread. Sounds like at least one of you has a doctorate in battery maintenance.

I always plug my MH in to 110 V power when we are home and let it there all the time. (mistake ????)

Also I will be putting the motorhome in my new pole barn in a couple of weeks as soon as the floor is poured and cures. I intend to leave it plugged in all winter to keep the batteries charged. I am assuming that the charger in the Motorhome "floats" and will not cook the batteries.

Am I correct in this?

And am I doing the right thing for my batteries?

[BatteryPro]

Originally Posted by Gerryl

...The info here on this thread is making my head spin…..I always plug my MH in to 110 V power when we are home and let it there all the time. (mistake ????)

Also I will be putting the motorhome in my new pole barn in a couple of weeks as soon as the floor is poured and cures. I intend to leave it plugged in all winter to keep the batteries charged...

Hi Gerryl,

The answer depends on what type of battery you have. There are two types of batteries that you likely have; Hybrid, sometimes called RV/marine, and deep cycle battery. All 6 volt batteries are deep cycle, some 12 volt batteries are true deep cycle but most are hybrid design.

Like many things in life, there is good, better and best.

If you have hybrid batteries, It is good to leave the RV plugged in. Most of them will do fine because of the plate materials they use (less antimony).

If you have deep cycle, it is good to leave your RV plugged in.

It is better to leave it plugged in and exercise the battery every 30 days by discharging it about 15% then fully charging it.

It is best to discharge about 15% and recharge every 30 days using a 3-stage charger, then test the specific gravity (SG) of every cell. If any cell is more than 0.015 SG lower than your highest SG cell, equalize your battery. After equalize is done, check the SG of each cell and equalize again if necessary. Make sure the internal temperature is not above 125° F. If it does, stop the equalize, let the battery cool, then start again. It's best to keep a log book of all cells and their monthly SG readings.

Originally Posted by Gerryl

...I am assuming that the charger in the Motorhome "floats" and will not cook the batteries.

Am I correct in this?

And am I doing the right thing for my batteries?

Some people think that a battery will boil. Some people refer tho this as “cooking” their battery. If this is what you mean by “cook”, let me explain:

boil
verb (with reference to a liquid) "reach or cause to reach the temperature at which it bubbles and turns to vapor…"

Here's a fact: batteries don’t boil. This is a common misnomer. When the cell voltage reaches about 2.35 volts per cell, evolution of hydrogen and oxygen off the plates begins. The higher the applied voltage is, the more and faster evolution takes place. It sounds and looks like boiling, but it's not. It's just bubbling. This is normal for all deep cycle batteries if they are being charged properly.

Taking care of flooded batteries is work! Most people don’t do any of this which is why most people ruin their battery LONG before it is worn out. I'm sorry if this makes your head spin but it is the simplest explanation I can give.

Larry

[Technobody]

Different question:

I have two 12 volt deep cycle batteries they are identical and purchased at the same time. We are full time RVers with a 5th wheel. However, we have parked the trailer for the month of November as my wife and I both have numerous Drs appointments. To be on the safe side I removed both batteries and stored them at my daughters we are staying for the month. I have the batteries hooked up in parallel with my smart charger attached. Positive from the charger on one battery and negative on the other. It takes 3-4 days to charge the batteries but shuts down when the charge rate goes down to 0.1 amps.
So I unplug the charger for a week and then plug it back in the beginning of the next week. What surprises me is that the charger indicates a low charge and goes back to a smart optimal charge mode and the cycle repeats.
What I can't understand is what is drawing the charge down when it isn't attached to any load.
Does anyone have any ideas?

[pasdad1]

Originally Posted by Technobody

What I can't understand is what is drawing the charge down when it isn't attached to any load.

Does anyone have any ideas?

The answer is "self discharge".

[TQ60]

Self discharge is part and the charger is the other.

Leaving charger connected to battery while unplugged could result in discharging battery as the charger may have a path from battery back to charger for feedback that may have a slight load that could discharge over time.

Unplug and lift one charger to battery connection.

[bluepill]

It is also possible that one or both of the batteries has an internal fault. Try charging only one at a time. Let the battery rest for 6 hours. Check the voltage. They should be about the same.

Great info here:

http://www.marxrv.com/12volt/12volt.htm

[Gerryl]

THANK YOU Dr. Larry (post #22).

I will print off your post to keep with my motorhome papers and will try to determine what type of batteries I have.