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landyacht318's avatar
landyacht318
Explorer
Feb 03, 2014

US Battery "finishing" charge recommendation

Please check out these USBattery manufacturer recommendations for 2 and 3 stage chargers.

http://www.wholesalesolar.com/pdf.folder/battery-folder/charging_instruction_2011_2.pdf

Quite a bit different that the Usual Bulk charge to a certain Absorption/acceptance voltage then revert to float voltage regimen that we have been accustomed to and what each converter/Charger algorithm decides for us is best for batteries and which we seem to accept and perhaps argue over a bit.

I've been disappointed with my Newish group31 USbattery performance until I rewired my Electrical system allowing my Schumacher to do its thing with no load on the battery, all loads being switched to the other battery.

Without worry of high charging voltages damaging anything in my system, I just let the Schumacher SC2500a go, and awoke to 15.84v yesterday morning and the battery taking 1.2 amps to hold that sky high voltage.

I checked water levels, fine. No indications of water loss. I took SG readings and surprisingly found them all where they should be( 1.275 or higher). Where as, in mid December, ~3 weeks after putting the battery into service and feeding it lower acceptance voltages(14.5) and a 13.1 float, all the Sg readings were in the red (1.220 to 1.240) despite not being able to force more amps into the battery at that time of dipping my Hydrometer.

Last night the battery performed admirable in terms of voltages under load, much much better than any time previously, and I drained it to ~55% in about 7 hours( intentionally being wasteful) and then removed all loads and let the Schumacher do its thing again, and again awoke to 15.8v, but only 0.6 amps to hold that voltage. NO SG readings taken today, but I suspect they would be higher and closer to each other than the day before.


I'm thinking of setting my Solar Float voltage at 15.3v as the "finishing" charge in daily cyclic usage. I'll lower that to 13.02v( recommended float voltage) If /when I stop cycling the battery.

Nothing in my system seems to not be able to handle 15.3v. I do have an AGM battery as my engine battery, but I do not need to subject that battery to these voltages if I so choose.

So lets discuss this 15.3v "finishing" charge recommendation which falls into the daily equalization category, and which I am kind of uncomfortable with.

Yet 15.8v for several hours it did allow the SG to rise where it should be, and performance to increase to what I expect from a new healthy respectable brand of Deep cycle battery.

I worry about positive plate shedding and overcharging with a daily 15.3v "finishing" charge, but lower voltages were obviously causing sulfation due to incomplete charging.

While the Schumacher is available, as is grid power, I'm hoping to reduce or perhaps eliminate needing grid power and use only to 200 watts of solar and my alternator to restore what I remove the night before, and hope to set my solar settings to best allow the battery to perform properly.

I know everything is a compromise, but what do you "battery nerds" think about this "15.3v finishing charge" recommendation?

90 Replies

  • landyacht318 wrote:
    Yes, I'm hoping that 15.8v is required only seldomly, and that if I set my float at 15.3, perhaps the solar can get them there and hold them there for a little while this time of year, After the Solstice I don't foresee an issue. Hopefully the performance I witnessed from the battery in question holds true with a 15.3v Float/finish.

    Does any other manufacturer have a 15+v daily recommendation and not just part of an EQ function?

    My solar is able to have both acceptance and float voltage adjusted where ever. the Schumacher is kind of random as to when it decides 14.8v is sufficient and when it will to 15.5+.

    Trying to start the Schumacher on a battery above 90% always cause strange issues


    I have the largest version of the Schumacher Speed Chargers, SC-12000A (120 amp engine start, 40-15 amp variable fast charge (multi-stage), 2 amp slow charge (no longer listed).

    My manual talks about the problem you see when charging a 90% charge battery(s). It states that charger will see the cut-off voltage too soon when used in multi-stage charging. The manual recommends using the "2 amp slow charge" on batteries showing a higher charge level to properly fully charge them. Otherwise; wait till the battery charge is lower before initiating multi-stage charging.
  • Interstate (which used to carry US Battery 6s) also has the over 15 thing for 6s so it must apply to their newer version Mexican 6s (GC2-XHD which I have a set of)

    My old 27DCs needed the Equalize thing after doing 50-90s too but they were a huge PITA to get the SG up. Love my 6s and T-1275s--they charge right up to SG baseline no fuss no muss.
  • Hey Don, how they hanging?

    I just checked my Danfoss compressor controller link, Safe to 17 volts for a 12v system and 31.5v for a 24v system.
  • Hi,

    Nice to hear from you!

    Fridge boards and others are rated at 15.4 volts. I think you could bump up to 15.5 safely as there is voltage drop on the lines. Certainly 15.4 would be safe.
  • Yes, I'm hoping that 15.8v is required only seldomly, and that if I set my float at 15.3, perhaps the solar can get them there and hold them there for a little while this time of year, After the Solstice I don't foresee an issue. Hopefully the performance I witnessed from the battery in question holds true with a 15.3v Float/finish.

    Does any other manufacturer have a 15+v daily recommendation and not just part of an EQ function?

    My solar is able to have both acceptance and float voltage adjusted where ever. the Schumacher is kind of random as to when it decides 14.8v is sufficient and when it will to 15.5+.

    Trying to start the Schumacher on a battery above 90% always cause strange issues
  • Sure looks like daily equalization to me. I might try a weekly one hour equalization and see how it goes. There is a break-in period for these batteries so don't be too hard on them yet.
  • I discovered the 15v inverter limit while doing solar direct and the voltage got over 15. Then I tried to use the MW to make supper and it wouldn't start.

    Next thing is to find something to run that has enough draw to get the batts down to 14.9 so the inverter would start. I used the furnace by sliding the temp all the way to the top on the thermostat (it was 80F in the trailer)

    When on solar in summer doing say 80-95s with solar controller at 14.6 that is still not getting them to 100 so every month at least I need to either do a solar direct trick to get them into the 15s or else find shore power and use my VEC1093DBD Equalize 15.8v on them.

    Once that is done, they are good to back on regular 80-95s to 14.6 or whatever the solar can do any particular day.

    (I could use my adjustable voltage PowerMax instead of the 1093, but the 1093 Equalize is automatic so I don't have to be there to shut it off at the right time.)
  • Well, I think I had to do a "recovery" as my voltage setpoints and running the Schumacher when the fridge was still cycling were undercharging it. I was very surprised by the In the red readings in December. All indications were that the battery was fully charged, and after reading so low, I could not get it to take anymore. I was planning on returning it after the Holidays and since then life has got in the way.

    I'm pretty sure my Danfoss compressor controller says the cut off is 16.5v when run on 12 volts nominal. Not sure about the inverter but am not sure the solar could hold 15.3v if I am running the inverter in Daylight hours.

    Which is another aspect, The voltage swinging when the fridge compressor kicks on.
    I need one more switch to divert solar to one battery or the other independent of load. Right now the solar is connected to the Common Load Stud on the switch.

    Not sure I have room for another switch.
  • I also do 15+V finish charges on my batteries otherwise they will show low SG just like you've discovered.
  • I have frequently posted about doing this, as you may know, but I only do the 15.8 trick once in a while as a "recovery" method after camping doing 50-90s or at least once a month on Float or when camping on solar. IMO it is essential for deep cycle batts like it says in that link and also on the Interstate site for 6s.

    For regular recharging I go to about 14.8. One thing about 15.3 while under the fridge limit, is that it is over 15 and some inverters have a high voltage shut down at 15v input.