Battery

[GeorgeTelford]

Hi Chris

Beware of so callled "charging" from the Vehicle alternator, a starter battery never gets much over 70% charged via the alternator. If you dont use the last 50% charge (and you should not on a normal lead acid) then that doesnt leave you a lot to play with 20 % of the total capacity. This improves with Traction batteries which are generally ok when discharged to 80% max.

Charging with a 3 or 4 stage charger fills the battery 100% so if you had a 100AH Battery you would get 50 Amps normal lead acid or 80 Amps via traction.

If you have fully charged at home and then drive with alternator charging in place by the time you arrive you could be back down to 70%

[Chris C]

Thanks for the info, George, but because of your comments in the past, I'd already decided not to charge from the tow vehicle. Still can't find a whole lot of info about traction batteries that makes me more interested in them than AGM types. (Also, is the Optima an AGM?)

[Chris C]

George, what are the attributes of the traction battery over the AGM? And once again, is the Optima an AGM battery? Sorry for all the questions. I know so little about this area.

[GeorgeTelford]

Hi Chris

Here are a couple of quotes and links that just about sum it up.

We've been using Trojan "Traction" batteries for years in our yachts. These industrial strength batteries are designed for a full 80% discharge, and guaranteed for 1500 cycles in industrial use. Last week we removed the batteries from the keel sump aboard Beowulf and sent them back to Trojan for service. We used a combination of main halyard and boat yard hydro-crane to remove them. It is somewhat over five years ago now that we purchased these batteries, and they have sat around for the greater part of this time - not a good thing for their capacity. Trojan took them in, cycled them to the 80% level twice, and then did a voltage check. The check is done at the discharged resting voltage. Turns out that these batteries are at 105% of rated capacity. Not bad after all these years. In chatting with Mark Waycaster at Trojan about maintenance, he emphasized several things (which apply to traction batteries and their marine batteries like the L-16):

http://www.setsail.com/c_central/techtalk/battery.html



Industrial deep cycle batteries
Sometimes called "fork lift", "traction" or "stationary" batteries, are used where power is needed over a longer period of time, and are designed to be "deep cycled", or discharged down as low as 20% of full charge (80% DOD, or Depth of Discharge). These are often called traction batteries because of their widespread use in forklifts, golf carts, and floor sweepers (from which we get the "GC" and "FS" series of battery sizes). Deep cycle batteries have much thicker plates than automotive batteries.

Plate Thickness
Plate thickness (of the Positive plate) matters because of a factor called "positive grid corrosion". This ranks among the top 3 reasons for battery failure. The positive (+) plate is what gets eaten away gradually over time, so eventually there is nothing left - it all falls to the bottom as sediment. Thicker plates are directly related to longer life, so other things being equal, the battery with the thickest plates will last the longest.

Automotive batteries typically have plates about .040" (40/1000") thick, while forklift batteries may have plates more than 1/4" (.265" for example in the Rolls-Surrette) thick - almost 7 times as thick as auto batteries. The typical golf cart will have plates that are around .07 to .11" thick. The Concorde AGM's are .115", The Rolls-Surrette L-16 type (CH460) is .150", and the US Battery and Trojan L-16 types are .090".

Most industrial deep-cycle batteries use Lead-Antimony plates rather than the Lead-Calcium used in AGM or gelled deep-cycle batteries. The Antimony increases plate life and strength, but increases gassing and water loss. This is why most industrial batteries have to be checked often for water level if you do not have Hydrocaps. The self discharge of batteries with Lead-Antimony plates can be high - as much as 1% per day on an older battery. A new AGM typically self-discharges at about 1-2% per month, while an old one may be as much as 2% per week.

http://www.windsun.com/Batteries/Battery_FAQ.htm#Industrial%20deep%20cycle%20batteries

[Chris C]

THANK YOU, GEORGE!!!!! That's exactly the kind of information I'd been looking for and couldn't find. (now to find a traction battery I can afford)

[DestinDave]

My plans are to use 2 Group 27 lead acid batteries (Interstate) rated at 105Ah each. My reasoning here is that I can get them at wholesale through the marina which is $54 each and at that price I can replace them yearly if need be. I think retail is about $80 or $85 each.
George - if I understand correctly, 2 of these will yield 210Ah but if used to 50% discharge I only get 105Ah of effective use before they should be charged. Is that right?
I also plan to connect them to the power panel with a marine-grade switch - one of those 1-2-both-off switches. Nothing wrong with that plan is there?

Dave

[GeorgeTelford]

Hi Dave

yes spot on 50% = 105 ah then get recharging.


The marine switch Idea, personally I am not keen because you dont actually gain any extra time/power (follow it through and you may actually lose some time/power, see next), when charging, you would have to charge them seperately otherwise the charger is going to see the "average of the 2 batteries" and charge neither well.

If they have been discharged slightly differently they will try to equalise when the switch is on "both" and battery to battery charging is wasteful.

If however they are charged seperately and discharged seperately and never get put on "both", there is the advantage of knowing you are down to last battery/reserve.

[mikeschn]

George,

I've been toying with the dorm fridge on a battery idea again...

As we know we are talking 600 watts surge, but about 150 watts running...

From your experience with your fridge running on 10 batteries, what can I expect from a dorm fridge running on say 2 or 4 batteries...

600 watts once an hour, 150 watts for 20 minutes per hour?

600 watts once every 30 minutes, 150 watts for 10 minutes every 30 minutes...

You get the idea...

And how low can the battery bank go before it will no longer handle the surge that the fridge demands of it?

Mike...

[GeorgeTelford]

Hi Mike

It will take 3 Amps per hour (thats my full size fridge, I would hope that a smaller fridge would take less), depending on fridge efficiency, over here they are rated with a yearly consumption too

so on 2 110 Ah batteries it would last 36.6 Hours (taking the batteries down to 50%) unless they are traction batteries then you can take 80% max then you would get 59 Hours

Double the above if you use 4 batteries, dont forget this may be better if the ampage on the samller fridge is better.

Have you got a particular model of fridge in mind?

[mikeschn]

George,

Let me run outside again and get the model number of my dorm fridge for you...

Okay it's the Haier HSW02C

Now let see if I can find the specs again...

Okay... here it is...

My Haier is rated at 1.4A Max Amps 5.3A

Mike...

[GeorgeTelford]

Hi Mike

that unit takes 307 kWHrs per Year

thats 841 Watts per Day

35 Watts per hour

2.9 Amps per hour @ 12v (without adding extra for invertor eff)

Gotta say thats very ineficient, the full size fridge I used only Averaged 3 Amps (that was measured pre invertor) To give you an idea the full size fridge worked out at 2.1 Ampsper hour @ 12v (withour adding xtra for invertor eff)

I would guess that all up its going to cost you 3.7 Amps per hour so with 2 batteries 30 Hours (60 Hours with 4 Batteries) 110 Ah batteries

2 Traction 48 Hours 4 Traction 96 Hours

The above assumes all batteries fully charged and never attached to vehicle charging.

Of course there are ways to increase eff, add extra insulation and improve ventilation away from back of fridge.