What Happens if I Charge MY Batteries Too Hard?

Feb 5, 2004
3,739
Tartan 3800 Westport, MA
I recently came to the awareness that my battery banks maximum recommended bulk charging current is 13% C(20); since I have two 115Ah flooded batteries in parallel, that comes out to 30A.

I have been charging them really hard. Since I installed the serpentine belt kit, 100A initially, but this tapers as bulk continues.

Two days ago I programmed the regulator current limit to 70A, thinking 60A plus 10 for loads, having made an arithmetic error, factor of two.

Should I cut it down to 30A plus 10A? Could I have damaged these batteries already?

(I just checked the water level, it's fine.)
 
Sep 25, 2008
5,424
Alden 50 Sarasota, Florida
It’s “acceptance” rate that determines how many amps are applied. As long as you aren’t heating them up too much, you are good
 
May 17, 2004
1,880
Beneteau Oceanis 37 LE Havre de Grace
The other thread on charging had this quote from Maine sail, which might give you your answer -

Trojan Batteries can certainly accept much more than .13C in charge current. Trojan's guidelines are really for golf course type charging and .13C is a good charge rate to go by if you have many hours to charge.

If you are limited in the amount of time you want to spend charging you can "fast charge" Trojan batteries at upwards of .25C to even .3C. Trojan may recommend .2C if they don't know what you have for charge equipment, temp compensation etc...
 
Feb 5, 2004
3,739
Tartan 3800 Westport, MA
It’s “acceptance” rate that determines how many amps are applied. As long as you aren’t heating them up too much, you are good
Thanks for the reply, @Don S/V ILLusion . In acceptance mode, a.k.a., absorption mode, you are correct. In bulk mode, that's not so. My batts will take whatever current I throw at them, even far in excess of Trojan's recommendation.
Thanks, @Stu Jackson . But I disagree. You can, indeed, charge a battery too hard in bulk mode, and per @Maine Sail 's comment: "upwards of .25C to even .3C," there is a limit.

I've been charging at 44% C(20), without temperature compensation. That can't be good.

Just as Maine suggests, Trojan says:

"Maximum Charge Current* (% of C20): 13% - *If charging time is limited contact Trojan Technical Support for assistance."

I'm going to give Trojan a call. Meanwhile, maybe someone can provide more insight into heavy bulk charging.

Just so it's clear, by "bulk," I mean the first stage of the typical 3-stage charging algorithm, which is typically a constant current charge up to the acceptance (absorption) voltage, at which point you switch to constant voltage until "full," typically when the current drops to 2%C(20).
 
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Feb 26, 2004
20,692
Catalina 34 224 Maple Bay, BC, Canada
Thanks, @Stu Jackson . But I disagree. You can, indeed, charge a battery too hard in bulk mode, and per @Maine Sail 's comment: "upwards of .25C to even .3C," there is a limit.
Somehow I knew you would. :)

One answer is it doesn't matter, 'cuz you don't seem to want to agree with battery acceptance being a limiting factor, as both Don and I have explained. You already said your bank doesn't get hot.

You could have a ZILLION amp charger, but your bank will determine how much it will take.

However, what IS part of the equation is a balanced system.

For example, your point is that you think your charger or alternator is too big for your bank.

However, another POV is that your bank is too small for your charger or alternator.

Have you considered adding more capacity to your bank? 2 x 115 = 230 ah, which is about half of what a "normal" house bank would be for a boat your size when cruising. I don't recall if you have a fridge or not. If you do, I can't figure out how you can spend a night on the hook, unless you also have solar.

As far as operation with your external regulator, have you considered simply using Small Engine Mode rather than dialing back your AO all the time with belt manager? I'm sure you've seen these, but here they are again:

Small Engine Mode - discussion with link to the picture of the toggle switch: http://c34.org/bbs/index.php/topic,4454.msg27149.html#msg27149

Small Engine Mode - the picture of the toggle switch http://c34.org/bbs/index.php/topic,4669.0.html

A simple toggle switch could answer ALL your concerns. Without any messy reprogramming.

I've had a 100A alternator, with an MC-612 and a Link 2000 in for over 15 years.

These are correct answers that you seem to want to disagree with.

Plus, didn't Davidsailor already answer your concern? AND, he even quoted Maine Sail!!!

Sure, go call Trojan, but what do you expect to hear?

BTW, I don't recall if I've mentioned this to you, but you have a really nice new boat. Congratulations on it.
 
Sep 25, 2008
5,424
Alden 50 Sarasota, Florida
If your charger is working properly and is reasonably current, it will lapse into absorption based on voltage sensing thereby precluding heating making this a moot point.
 
Feb 5, 2004
3,739
Tartan 3800 Westport, MA
@Stu Jackson , let's try to keep it civil, not personal, O.K.?

What I am asking, very specifically, is, what happens - i.e., what damage may I incur - if I charge my batteries too hard during bulk. That's it. Trojan recommends 13% C(20). MaineSail says they will allow 25%, even 30%. I'm saying that I can easily far exceed this.

So, until I hit the acceptance voltage, what damage am I causing, if any? I can charge during bulk at 100A, which is 43% of C(20). If its not a problem, why does Trojan recommend a lower value?

Perhaps they will get too hot? Shorten their life? Drive to acceptance voltage too soon? (resulting in a partial charge.) I don't know. That's why I asked.

BTW, I'm using Link 2000-R F10, alternator output limiting. Nothing about small engine mode.

Maybe it's O.K. to charge during bulk at 43%, 50%, whatever. Who knows?

@Don S/V ILLusion this has nothing to do with acceptance mode.
 
Feb 26, 2004
20,692
Catalina 34 224 Maple Bay, BC, Canada
1. BTW, I'm using Link 2000-R F10, alternator output limiting. Nothing about small engine mode.

2. Maybe it's O.K. to charge during bulk at 43%, 50%, whatever. Who knows?

3. @Don S/V ILLusion this has nothing to do with acceptance mode.
1. I see, guess your regulator doesn't have temp compensation then. Is that correct?

2. Seems that's been asked and answered. Part of the answer is #3 below.

3. With a relatively small bank compared to your 100A alternator with serpentine belt, wouldn't one expect the bulk phase to be quite short? You're putting in constant current with most likely a RAPIDLY rising voltage. Isn't that what your Link is showing? When I get back to my slip with a depleted battery bank, my bulk phase is rather short with my 400 ah bank and my 75A charger, because the battery acceptance level gets smaller very quickly. As far as I know, battery acceptance has nothing to do with bulk, absorption or float, it exists all the time and is not limited to any particular phase.

Perhaps you can comment on how long your bulk phase actually takes.
 
Feb 5, 2004
3,739
Tartan 3800 Westport, MA
1. I see, guess your regulator doesn't have temp compensation then. Is that correct?
I believe it's capable, but I don't have a battery temp probe. But, that would only control acceptance voltage, not current during bulk mode.
2. Seems that's been asked and answered. Part of the answer is #3 below.
I don't think so. That's the question I'm asking.
Perhaps you can comment on how long your bulk phase actually takes.
I don't recall, exactly, but it doesn't take very long. From a bank that's at 60% SOC maybe 1/2 hour? I'll have to check next time I charge.
my bulk phase is rather short with my 400 ah bank and my 75A charger, because the battery acceptance gets smaller very quickly.
Maybe this is where we're getting hung up. What exactly do you mean by your battery acceptance? During bulk you should be at constant current, and the voltage rises towards the set acceptance voltage. Then, it shifts into acceptance mode, and charges at constant voltage 'til the current drops to about 2% of C(20). Right?
 
Feb 26, 2004
20,692
Catalina 34 224 Maple Bay, BC, Canada
Maybe this is where we're getting hung up. What exactly do you mean by your battery acceptance? During bulk you should be at constant current, and the voltage rises towards the set acceptance voltage. Then, it shifts into acceptance mode, and charges at constant voltage 'til the current drops to about 2% of C(20). Right?
Perhaps there is confusion about the word acceptance. BTW, I seem to recall that the 3 phases of charging (or stages) are bulk, absorption and float, not bulk, acceptance, and float.

Edit: I read the Link 2000 R manual, and it does say "acceptance." Most likely where you got that.

Battery acceptance is the ability of the bank to absorb current, and is not a phase or stage of charging. That's all. The fuller a battery is, the less current it can and will take, regardless of what phase or stage of charging one may be experiencing.

If you have a small bank compared to your charging SOURCE (so we can dispense with typing 'charger or alternator' from now on :)), the bulk phase would be expected to be very short, because one is providing a LOT of current with a rapidly rising voltage. One will reach the voltage setpoint rather quickly, and, as you correctly stated, the current will begin to decline. That current reduction is due solely to battery acceptance. At any given pressure, i.e., voltage, the flow, i.e., current, will decline.

The regulator is NOT telling your charging source to reduce the current. The battery acceptance is "pushing back", if you will, against whatever current could be available IF the voltage hadn't stopped rising.

[EDIT: Your F10 function is a safety device and does not affect this discussion about battery acceptance. This is because you have the AO shunt, which most other popular, i.e., Balmar, external regulators do not have, a shunt. Its end result is identical to the functions used by Balmar called amp or belt manager.]

Once the voltage setpoint is reached, it's the battery acceptance that controls the current that can be absorbed.

See, that's why English sucks for engineering stuff!!! :):):) Acceptance, absorption, accept, absorb, phases, stages...yadayada :)

Anyway, even with my house bank which is twice the size of yours, but with my 75A shorepower charger, I see this all the time when I come back from a day long day sail. The bulk phase simply doesn't take very long. In the over two deacdes since I have had this system, I have never had any issues with overcharging during bulk, because it simply doesn't last that long. You may choose to go back to re-read what I've said now with perhaps a better understanding of why I said what I did.

I don't know how familiar you have gotten with your Link. First, have you read my "Gotcha Algorithm" article? If not, I'll send you a link to it, helped to develop it thanks to Rich Stidger and Donalex, both on this very forum. It's important. Second, I have attached a little known but important document that I "captured" shortly after I bought my boat and my Link 2000. The info in it is NOT in either the Link 2000 or 2000-R manuals. Hope you don't ever need it, but I have, twice so far in 20 years, once just last month. Hope it helps if you need it.
 

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Jun 11, 2004
807
Oday 31 Redondo Beach
Trojan says:

"Maximum Charge Current* (% of C20): 13% - *If charging time is limited contact Trojan Technical Support for assistance."

I'm going to give Trojan a call.
Interesting back and forth. I think it is only going to be answered by what Trojan says about why they say maximum charge current is 13% of C. Why do they say it that way? What do they say will happen if current is over 13% of C?

I'm sure jviss will report what they tell him.
 
May 17, 2004
1,880
Beneteau Oceanis 37 LE Havre de Grace
Have you read reply #3 from Davidsailor?
The point I took from the Main Sail statement I quoted was that there is some maximum allowable charge rate in bulk. 0.13 might be an overly conservative estimate of that rating, but even Maine seems to say that going over 0.3 is not ideal. Now, as you say, the bank might only stay in bulk at an amperage above that for a short period of time, but still I think it's an interesting question to ask if exceeding those values is damaging.
 
Feb 5, 2004
3,739
Tartan 3800 Westport, MA
That current reduction is due solely to battery acceptance. At any given pressure, i.e., voltage, the flow, i.e., current, will decline.

The regulator is NOT telling your charging source to reduce the current. The battery acceptance is "pushing back", if you will, against whatever current could be available IF the voltage hadn't stopped rising.
That current reduction is due to the regulator holding the voltage constant once you reach the absorption voltage. For example, if you program the absorption voltage to be 14.4V, that is the point at which the current will begin to decline; if you program the absorption voltage to be 14.8V, that is the point at which the current will begin to decline. If you never stopped pumping current, you would eventually start boiling off electrolyte, the battery would heat up, it's internal resistance would decrease, and you'd get in to a thermal runaway condition.

There's no such thing as a battery "pushing back." The constant voltage is impressed upon the terminals by the regulator, and the battery absorbs charge according to its chemistry, which results in the current decline.

But that's really beside the point. The question from the first post is "what happens with higher than recommended currents during the bulk charging phase?"
 
Jun 1, 2007
3,313
Macgregor 26S Hobie TI, Capri Coronado 15 Denver, Colorado
Cant answer your question.. will be interesting to see what the manufacture says. But one thought somewhat related is that if you are charging them with a lot of current in bulk, measuring temperature at the battery and a charge controller that acts on that temp would seem more important. For any given charge state, battery voltage goes down with increasing temperature, ie, a negative temperature coefficient. So without the temp sensing, the regulator is trying to bring the voltage to 14.4 (for example) before going into absorption. But lets say the rapid charging caused the battery to heat up some (which might be OK) but at the higher battery temperature, absorption target should have been 13.9 (just an example , temp co. is easy to find) but without temp compensation, you took it up to 14.4. How bad is doing that.. dont know.

Small solar charges will have just internal ambient temp measurement as the current is generally not high enough to cause the battery to heat up. But as you go up in current, it seems that most regulators of any type will measure temperature right at the battery because the charging is likely to cause the battery temp to increase.
 
Feb 5, 2004
3,739
Tartan 3800 Westport, MA
Cant answer your question.. will be interesting to see what the manufacture says. But one thought somewhat related is that if you are charging them with a lot of current in bulk, measuring temperature at the battery and a charge controller that acts on that temp would seem more important. For any given charge state, battery voltage goes down with increasing temperature, ie, a negative temperature coefficient. So without the temp sensing, the regulator is trying to bring the voltage to 14.4 (for example) before going into absorption. But lets say the rapid charging caused the battery to heat up some (which might be OK) but at the higher battery temperature, absorption target should have been 13.9 (just an example , temp co. is easy to find) but without temp compensation, you took it up to 14.4. How bad is doing that.. dont know.

Small solar charges will have just internal ambient temp measurement as the current is generally not high enough to cause the battery to heat up. But as you go up in current, it seems that most regulators of any type will measure temperature right at the battery because the charging is likely to cause the battery temp to increase.
Thanks, Walt, that's very insightful, and well stated. However, I don't think missing the exact absorption charge voltage would have a serious affect on the battery health. I'm more interested in what damage the heavy current in bulk might do.

For the absorption voltage Trojan says to subtract 0.0028 volt per cell for every 1°F above 77°F. So, at 97º you should be at 14.464V instead of the 25º C recommended voltage of 14.8. And, once the current drops entering absorption phase, the temp would drop, too. Make sense?
 
May 24, 2004
5,855
CC 30 South Florida
Yes I have. It is a quote from Maine Sail. I don't disagree with it but I don't see how it really answers the question as to why Trojan recommends a max charge amperage of 13% of C.
Golf Cart Batteries. Recharging mostly done overnight, slow and easy on the bulk for Battery Life.
 
Jul 23, 2009
178
Beneteau 88 First 285 Grand Lake, Oklahoma
Trojan does say for a solar application to size the solar array to 10 - 20% of the Ah of the bank. This makes me think that 20%C is fine.
Battery charging is a compromise, kinda like a boat.
 
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