When is a battery charged?

Becky

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This is for the very clever electrically minded among you. We have 2 chargers, Mobitronics, a 45 amp for the domestic batteries, and a 25 amp for the engine battery. The batteries are monitored by a Mastervolt thingy that tells us everything we could possibly want to know. At the moment the batteries are reading 13.88 volts, and 61 amp hours down. We also have a 90 amp alternator and an Adverc smart controller, which has the ability to raise the battery voltage higher. When motoring, we can get a 100% reading on the monitor, as opposed to about 80% just with the chargers. So.... which is right? Is the Adverc overcharging, orthe Mobitronics undercharging?
I doubt that it really matters, but I would like to know, & HWMBO doesn't know!! Which to be honest is a fact worth recording on its own anyway./forums/images/icons/smile.gif

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pvb

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Sounds like...

Sounds like the Mobitronic charger is switching from absorption to float voltage before the batteries are fully charged. I'm not familiar with Mobitronic chargers, so don't know whether the absorption time might be adjustable. It would be worth checking the manual for your charger.

My experience is just like yours - when motoring, my Adverc system recharges the batteries more fully than the mains charger.





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Robin

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Re: Sounds like...

On our last boat the Adverc/alternator was much better than the original mains charger, then we changed to a Poweramp Hawk which was almost as good as the Adverc. On our latest boat the Adverc was much better than the original so-called smart but downright stupid Newmar, but that has now been replaced with a Sterling Pro on which the jury is still out - I would guess it is pretty good but maybe not quite as good as the Adverc.

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johna

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With batteries at 13.88 I should think you could sell power to the National Grid so why worry what is doing what. Being a little more serious if you have an Adverc or similar system do you really need a top of the range battery charger? Discuss.

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Robin

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Hi John, I guess you didn't go golfing today either!.

I think she means the voltage is 13.88v on float with the charger on, actually a tad higher than ideal maybe, I think ours is 13.6v.

When we are away cruising we spend a lot of time at anchor, so when we go into a marina for food/fuel/water and maybe a meal out I also like to top up the batteries to as close to 100% as I can. That way we have no need to run the engine any longer than is needed when we leave. At anchor we have wind and solar power too but if we need to motor then the Adverc ensures at least we get 100% battery charge as some compensation for having to motor!

Robin



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A

Anonymous

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The most probable reason for this happening is that the batteries must be taken to around 14.5V to finish the charging off otherwise your plates will 'sulphate', which is irreversible. You should take the voltage up to this level every time the batteries are significantly discharged - say by more than 20% or so. Most chargers do this automatically. The Mastervolt monitor is looking for this voltage to have been achieved and for a preset period - I don't know whether Mastervolt products are programmable or fixed. Maybe the Mastervolt is looking for a period longer than the Mobitronic is giving but it doesn't follow that this is not long enough for the care of the batteries.

When the Mastervolt monitor is satisfied, the display goes back to 100% (or whatever Ahr you have progammed in for your battery bank). We really don't know when it is doing that unless you watch the voltage quite carefully the next time the batteries are recharged following a reasonable period of discharge both with the Adverc and the Mobitronic. If you take the batteries to 14.5V for fifteen minutes I think you will be OK, after that, the voltage should fall back to the float level of 13.6 to 13.8 depending on temperature and the type of battery.

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snowleopard

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to tell whether your battery is fully charged you need to test it with a hydrometer or let it settle for several hours after charging and check the voltage. 12.8v is full. the 13.8 with the charger on or recently switched off is meaningless.

don't know what logic the mastervolt uses but our link 10 computer resets to 100% after 20 mins of charge current below 1.5% of the battery capacity (e.g. 3A for a 200AH bank) and voltage over 13.5. can't remember the exact figures but it's something like that.

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Becky

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Thank you everyone for your input. I am getting more of a picture of how this business works now. We made a fundamental mistake in checking the batteries while the chargers were on, so we actually only measured the ingoing output of the chargers, if that makes sense (?). What I believe to happen is that the Adverc has the ability to raise the state of charge of the batteries to a higher level than the Mobitronics, so that the Mastervolt thingy resets itself to the higher level, so that when we aren't using the engine, the Mobitronics leave the apparently false reading of not being fully charged up. We have seemingly 61 amp hours unfilled.
Still, everything seems to be working OK, so I think that we will just leave it alone. But will discuss with Bardon Batteries who are just local to me, when we get some more batteries for the domestic bank.

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Robin

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Becky

Yes you are correct in that it is the voltage from the charger once it has dropped from full charge output to a float voltage that you have measured. It is worth ringing Waeco who I believe are the Mobitronics people and asking if your chargers have any adjustments for different battery types ie different maximum voltage setting. Another possibility might be if your wiring is such that the output of one of the chargers doesn't go though the Mastervolt thingy so it's contribution doesn't get added in?

One thing to try is switch the chargers off and then back on again so that they start their cycles again from the beginning, then see if that reduces the shortfall on the Mastervolt meter.

Of course you could just go low tech and measure the Specific Gravity of each cell with a hydrometer, actually the most accurate way of doing things. You will only be able to do this if you have wet batteries rather than sealed gel types. Hydrometers will be found in auto accessory stores like Halfords, cost only a few pounds and can be stored in a piece of PVC drain tube with a couple of bungs - don't let the acid drip anywhere unless you like perforated clothes....

Robin

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B

bob_tyler

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I just though that I would test the batteries on my car and my daughter's as neither had run today. Both are sealed batteries and both read 13.6 volts. Both are about 6 months old.

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pvb

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Mastervolt thingy....

What sort of Mastervolt thingy do you have? Some are "intelligent"; others aren't. It affects the info you get from them.

Adding more batteries to the domestic bank is the most cost-effective improvement you can make to the system.

PS Is Spangle Bessie's friend?

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A

Anonymous

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>>I just though that I would test the batteries on my car and my daughter's as neither had run today. Both are sealed batteries and both read 13.6 volts. Both are about 6 months old.<<

That's what you'd expect. There is a tiny current, of course, to the clock, door electronics, etc., and internal leakage but it's trivial over a day or so. An ideal float charger will not do more than replace exactly what the load is taking, plus the internal leakage. If it puts in any more than that on a long term basis it can harm the battery (so says one very reputable manufacturer but I have not yet determined the mechanism of this damage). So 13.6 indicated on a DMM - i.e. probably somewhere between 13.5 and 13.7 - is bang on, as is the OP's float voltage.

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A

Anonymous

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>>I believe you are assuming Bob's got the alternator running in your response ?<<

Yes, indeed. I didn't word it very clearly, sorry. /forums/images/graemlins/smile.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/tongue.gif /forums/images/graemlins/wink.gif

Just had to test the emoticons! /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif
 
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