Charging Voltages?

[Dockhead]

I have 8 Trojan 27TMX 12v batteries on board, wired to create a 420 amp/hours x 24v nominal house bank. These batteries are relatively cheap for Trojans, and although they are marked "deep cycle" I suspect that they are glorified "leisure batteries". I have therefore treated them like leisure batteries and have not let them get below a 50% charge, although they did get accidentally discharged to 0% and left that way for a few weeks once (from which they seem to have fully recovered -- a credit to Trojan).

I have a Victron Multiplus charger/inverter which failed last fall. After warranty service, I just reinstalled it. This time, I actually programmed it (before I just left it on its default settings).

In the process of programming it, I got confused about charging voltages. The default settings, for "Victron Gel Deep Discharge" and "Victron AGM Deep Discharge" batteries are 28.8 volts absorption (equivalent to 14.4 volts), 27.6 volts float (equivalent to 13.8 volts), and 26.4 volts "storage" (equivalent to 13.2 volts).

Trojan offers only one set of charging voltages for all of its batteries, although some of them are true traction golf cart types and others seem to be more like leisure batteries -- surely they are not all the same. Those are:

"Daily charge" (what is that? absorption?) 29.6 volts (14.8 volts)
Float 26.4 volts (13.2 volts)


So I set the Victron to the settings for "AGM Victron Deep Discharge Tubular Plate or OPzS batteries, AGM spiral cell". The voltages are 29.4 volts absorption (14.7 volts), 27.6 volts float, 26.4 volts "storage".

I also set the charger to give the full 70 amps of charging capacity, which would make a 0.166C charge.

Now the batteries gas and bubble vigorously during absorption charge -- I wonder if this is too high? It will certainly mean a lot more watering of the batteries, if I leave the settings like this.

The Victron fortunately has a clever mode which will reduce the absorption time proportionately if the bulk time is less, so that it doesn't give a full 8 hours of absorption charge after a shallow discharge.

After 24 hours with no discharge, the Victron will also go over to "storage mode" at 26.4 volts, applying an absorption charge once a week thereafter.

What do y'all think?

[btrayfors]

The Trojan 27TMX batteries are flooded type, not AGM.

Deep cycle batteries should generally not be discharged below about 50% SOC. They'll last longer if you don't cycle them much lower than that on a regular basis.

Letting batteries sit with less than a full charge will cause significant sulfation on the plates, thereby reducing their capacity. They may "hold a charge" thereafter, but it's quite likely that their capacity has been somewhat reduced. Only way to know is to test them with a good (and expensive) tester like the Midtronics series, or do a controlled discharge with a C/20 load.

Absorption voltage should be about 29.2-29.6VDC.

The Victron Multi-Plus chargers have many adjustable parameters, as well as an equalization mode. It would probably be beneficial to do an equalization since your batteries were sitting for awhile discharged.

While there should be some bubbling during the absorption phase, you should not see "vigorous bubbling". Check to be sure the batteries are not heating up. WaterMiser or Hydrocaps can reduce water loss.

Bill

[Dockhead]

Originally Posted by btrayfors

The Trojan 27TMX batteries are flooded type, not AGM.

Deep cycle batteries should generally not be discharged below about 50% SOC. They'll last longer if you don't cycle them much lower than that on a regular basis.

Letting batteries sit with less than a full charge will cause significant sulfation on the plates, thereby reducing their capacity. They may "hold a charge" thereafter, but it's quite likely that their capacity has been somewhat reduced. Only way to know is to test them with a good (and expensive) tester like the Midtronics series, or do a controlled discharge with a C/20 load.

Absorption voltage should be about 29.2-29.6VDC.

The Victron Multi-Plus chargers have many adjustable parameters, as well as an equalization mode. It would probably be beneficial to do an equalization since your batteries were sitting for awhile discharged.

While there should be some bubbling during the absorption phase, you should not see "vigorous bubbling". Check to be sure the batteries are not heating up. WaterMiser or Hydrocaps can reduce water loss.

Bill

Thanks, Bill, yes, I should have mentioned -- the Victron charging programs mention Gel and AGM batteries -- I am well aware (!) that my Trojans are flooded. That's one source of confusion -- Victron doesn't have any program for simple, regular flooded batteries.

I think that true traction batteries with heavy plates can handled discharges deeper than 50%, and the Trojan literature (http://www.trojanbattery.com/tech-su...nglish_003.pdf) seems to imply that an 80% discharge is ok. For this particular battery, which is not heavy enough for its capacity to be a real traction battery, I don't believe it and therefore follow the 50% rule.

I do regularly check specific gravity and I own a very good battery tester -- an Argus pulse tester (the same kind our own Maine Sail uses) -- which I use regularly, and log the results. I am pleased that despite my dead discharge incident, my batts are testing as good as when I installed them. I hope they will give me a few more years of service -- enough for LiFePO4 batts to become fully developed

Naturally I understand equalization and I do do that regularly. It's important in my case because my boat lives on a mooring without shore power, which is a hard life for batteries.

My batts don't get hot while charging (it's only .166C charge max), and the Victron as temperature sensors on the batts which will cut back the charge current in case of a temperature rise. Nevertheless, they are now gassing pretty vigorously at the new absorption rate of 29.4 volts, and I was just wondering if this absorption voltage is really ok for this type of battery? I don't trust the Trojan manual which lumps my obviously lighter duty batteries together with their true traction batts. The Victron manual likewise is no help, with all their Gel and AGM references in the charging programs.

[noelex 77]

Trojans absorption voltages are very aggressive. Usually I recommend sticking to the manufacturers specification, but I would be inclined to go slightly lower. (Why don't they include a custom charge profile on the Victron?)
The tubular plate setting looks like the best option. the absorption voltage is 0.2v below the recommendation which is just about ideal. The float charge is slightly high (1.2v) but the Trojan recommendation is very low and this wont give any problems. Importantly for long term storage it will drop to a nice low (and recommended 26.4 v )

My only concern is that with this high absorption voltage the absorption time is critical.
The batteries must be dropped back to float at the appropriate time.

This is usually defined as when they are accepting 2% of charge at the absorption voltage. For 420AHrs this is 8.4A going into the battery.

The default charger absorption time at 8hrs is very long (most are only 1or 2 hours). As you note the charger will modify this based on the bulk time, but I suspect from your description of the vigorous bubbling that the charger is staying in absorption mode too long. I have not used this algorithm so I don't know how well it performs in practice.

You need to do some measurements, or some arithmetic (if your battery monitor does not show the amps into the battery as most don't) and see when the charger is dropping back into float.

If it is correctly and appropriately dropping back to float (when the current going into the battery at close to the absorption voltage is down to about 8.4 A) I think the tubular wound battery setting are ideal.
If the battery return amps are lower than 8.4A on average, a lower absorption voltage would be a better compromise.

[Dockhead]

Well, batteries with heavy plates need higher charging voltages. What bugs me is the "one size fits all" voltages in the Trojan literature. I guess what I'm asking is whether or not 29.4 volts (14.7) is too high for a regular leisure type battery, or not? I'm sure it's fine for a real traction battery.

[noelex 77]

As a general rule for wet cell batteries overcharging does not shorten the life very much.
Most die from undercharging rather than overcharging.

For generator equipped boats a high absorption voltage has the advantage that you are squeezing as much power into the battery in as short a time as possible.
(Although battery efficiency does drop, so the gain is not as high as might be expected)

Most wet cell batteries from any manufacturer will cope fine with an absorption voltage 14.7v, but this high voltage the absorption phase must be terminated correctly.

[CharlieJ]

Drop Trojan Tech Support an email and ask them specifically.

VEConfig, the Victron programming software, allows the user to develop a custom charging profile. My Windows computer has failed, again, so I can't readily pull up VEConfig to give you a step by step.

[SURV69]

I don't know much about charging batteries, but I know that they don't like being cooked.

I also believe that slow charging is safer overall than fast charging and that charging at 10-20 amps might take longer, but should be better(for the batteries), than charging at 40-100 amps.

If they're bubbling "vigorously", they're cooking . . . get the hot dogs.

[FruiVita]

I'm wondering about the risk of leaving the boat connected to shore power with the battery charger on. And what if the battery switch is also set to "both"? Absent-minded captain, you know. ::

[Boracay]

My battery charger came with the caution that sparks could occur in the event of failure! In particular they cautioned against mounting it near flammable liquids!

My feeling is that provided the charger is in a well ventilated relatively spark proof place without any serious other combustibles then it may be OK.

That said I'll leave the charger on if I leave the boat. I won't leave it on while I'm sleeping.

Mind you, I have reduced the solar charge voltage down to 13.2V (from 14.8V recommended) as the batteries were getting a bit dry.

[noelex 77]

Originally Posted by Boracay

Mind you, I have reduced the solar charge voltage down to 13.2V (from 14.8V recommended) as the batteries were getting a bit dry.

Batteries are quite sensitive to small differences in charging voltages. 14.8v is on the high side, but dropping to 13.2v is a drastic change ( is it typo did you mean 14.2v?)
I would suggest a small drop to say 14.6, or at the most 14.4v. 0.2v will have a significant effect on the gassing.

Don't forget temperature compensation. This does not have to be automatic. A manual change of the set points as the seasons change is usually OK. Less so in southern Australia with its 4 seasons in one day, but a manual change is fine for QLD. Because batteries are located low down they are sometimes influenced more by water temperature than you would imagine.

[Fuss]

Originally Posted by Dockhead

I have 8 Trojan 27TMX 12v batteries on board, wired to create a 420 amp/hours x 24v nominal house bank. These batteries are relatively cheap for Trojans, and although they are marked "deep cycle" I suspect that they are glorified "leisure batteries". I have therefore treated them like leisure batteries and have not let them get below a 50% charge, although they did get accidentally discharged to 0% and left that way for a few weeks once (from which they seem to have fully recovered -- a credit to Trojan).

I have a Victron Multiplus charger/inverter which failed last fall. After warranty service, I just reinstalled it. This time, I actually programmed it (before I just left it on its default settings).

In the process of programming it, I got confused about charging voltages. The default settings, for "Victron Gel Deep Discharge" and "Victron AGM Deep Discharge" batteries are 28.8 volts absorption (equivalent to 14.4 volts), 27.6 volts float (equivalent to 13.8 volts), and 26.4 volts "storage" (equivalent to 13.2 volts).

Trojan offers only one set of charging voltages for all of its batteries, although some of them are true traction golf cart types and others seem to be more like leisure batteries -- surely they are not all the same. Those are:

"Daily charge" (what is that? absorption?) 29.6 volts (14.8 volts)
Float 26.4 volts (13.2 volts)


So I set the Victron to the settings for "AGM Victron Deep Discharge Tubular Plate or OPzS batteries, AGM spiral cell". The voltages are 29.4 volts absorption (14.7 volts), 27.6 volts float, 26.4 volts "storage".

I also set the charger to give the full 70 amps of charging capacity, which would make a 0.166C charge.

Now the batteries gas and bubble vigorously during absorption charge -- I wonder if this is too high? It will certainly mean a lot more watering of the batteries, if I leave the settings like this.

The Victron fortunately has a clever mode which will reduce the absorption time proportionately if the bulk time is less, so that it doesn't give a full 8 hours of absorption charge after a shallow discharge.

After 24 hours with no discharge, the Victron will also go over to "storage mode" at 26.4 volts, applying an absorption charge once a week thereafter.

What do y'all think?

They have to gas to mix the acid, your comment about bubbling suggests to me that you have been undercharging them.
Batteries are on a sailboat normally undercharged, ram it in at 29.6v especially on motor and generator.
The multiplus has a manual setting too but 29.6 absorbtion and float of 26.4 and equalisation of 31 is trojan specs.
Single point watering system would make your life easier.
Do an equalisation at 31v for a couple of hours and then do another one a week later to see if they settle down. but bubbling is good.

Here is the trojan link with charging specs...
http://www.trojanbattery.com/pdf/TRJ...UsersGuide.pdf