Batteries?? 7 6v vs 4 12v vs 6 8v

[wbhess]

I had put some thought into going the 8 6v route however, I was concerned I'd have trouble finding a charger that would handle all the extra capacities. 7 Batteries fit perfect in my tray and I'd have to rig up a secure method for my 8th battery in the bagwell. I currently have the 42v DPI charger and it works great. I had questioned on whether or not the DPI 48v would fully charge and maintain the 8 6v pack.

[JohnnieB]

The DPI will work fine, and so will most other 48V cart battery chargers, it'll just run longer when you go further.

Whatever power (kWh) you take out of the battery pack has to be returned to it, plus 15% to 25% due to the inefficiencies in the process. So charging a 10kWh battery pack that has been discharged to 50% SoC takes the same charger about 20% longer to recharge than a 8kWh pack discharged to 50% SoC.

I'm not as fond of DPI as I was before they kowtowed to the Republik of Kalifornia and stopped doing float charging.

If I was going to a 8x6V high capacity battery pack and often making long trips, I'd take a look at the Lester Summit II 1050W charger, it puts out 22A @48V. If I wasn't going to be making long trips nearly every day, I'd go with the 650W unit that puts out 13.5A @ 48V.


The size (output amps) of the charger needed is more or less determined by the downtime between uses and length of normal trips.

[cgtech]

I thought that Trojan wanted a 20+ amp charger for T-105 batteries, guess I could be wrong, based on this. Am I still wrong? If so, let me be corrected. I might be, based on this

[JohnnieB]

Originally Posted by cgtech

I thought that Trojan wanted a 20+ amp charger for T-105 batteries, guess I could be wrong, based on this. Am I still wrong? If so, let me be corrected. I might be, based on this

Your not wrong, 10% to 13% of AH capacity at the 20 hour rate is what Trojan recommends, which would be 22.5A to 29.3A for a 225AH T-105. US Battery recommends ~10%. So it appears that not many of the charger manufacturer's out there build golf cart battery chargers that meet the battery manufacturer's charging recommendations, either now or historically.

More correctly, there are quite a few 36V chargers that meet, or get pretty close to the battery manufacturer's recommendations, not as many at 42V and almost none at 48V, but unlike 36V and 42V, 48V packs can also be put together with lower AH capacity 8V or 12V batteries and with only two exceptions, 10% of their AH rating would be in the 15A to 17A range.

In the overall scheme of things, I guess as long as the charger has time enough to complete its charge cycle in the cart daily downtime, the amp rate is high enough. But I might be wrong.

[wbhess]

Since my 7 6v pack is closing in on 2yrs old, if I wanted to add another 6v battery in the mix now, could I still get 2-3 more years out of the total pack? I know its not good to add a new battery into an older pack, and its wisest to change all batteries at the same time. I am very, very cautious on not running my pack down beyond 50% soc and my pack now is in pretty good shape. If I were to buy a new 6v battery with the same AH rating as my current batteries, will it run down my older batteries quicker or will it run down my new battery to the condition of my old batteries.

[cgtech]

It's not gonna harm your cart. Just throwing money into a new battery that will soon be "just as old" internally as the others.

[JohnnieB]

Originally Posted by wbhess

Since my 7 6v pack is closing in on 2yrs old, if I wanted to add another 6v battery in the mix now, could I still get 2-3 more years out of the total pack? I know its not good to add a new battery into an older pack, and its wisest to change all batteries at the same time. I am very, very cautious on not running my pack down beyond 50% soc and my pack now is in pretty good shape. If I were to buy a new 6v battery with the same AH rating as my current batteries, will it run down my older batteries quicker or will it run down my new battery to the condition of my old batteries.

Therein lies the secret.

One of the "secrets" of battery pack longevity is matching the storage capacity of the batteries as closely as possible, and each battery's storage capacity diminishes slightly with every discharge/charge cycle. No two batteries are exactly the same at birth and for most of us, getting the same make/model of batteries with the same date code is about as close as we can get. Since the set of batteries are charged and discharged in series and are subjected to the same environmental conditions, they lose storage capacity at very similar rates, so their ever decreasing storage capacities stay fairly closely matched.

However, after two years use, they most definitely have significantly less storage capacity than they had when new, so adding a new battery that is the same make and model will create a pack with mismatched storage capacities, which reduces the future life expectancy of both the old and new batteries. This is pure speculation, but if the well matched 2 year old 42V pack had about two more years of useful life, the mismatched 48V pack might only last another year to 18 months.

The best answer is find the same make/model battery that is in good health and has been used about two years or so.

FWIW: If you had access to a load tester designed for golf cart batteries, find a battery whose run time at 75A is the same as the existing 6V batteries in the 42V pack. (Runtime tracks storage capacity)

[cgtech]

Just for fun, I'll throw this in the mix. According to this, batteries that are at 1/2 lifespan are in their plateau of performance. Also of note, it took over 100 cycles to reach peak capacity, and roughly 100 to reach their rating.

[JohnnieB]

Originally Posted by cgtech

Just for fun, I'll throw this in the mix. According to this, batteries that are at 1/2 lifespan are in their plateau of performance.

Love to know what the parameters were on that test as well as the specs for a 1993 era T-105 battery.

Current specs for a T-105 is 225AH at the 20 hour rate and 115 minutes runtime at a 75A discharge rate. The graph has a line a bit below the 110 minute line for the minute spec, (107 or 108 minutes ?)

The test ran from 1/11/93 to 5/5/94 (480 days inclusive) and the failure occurred at 679 cycle, so more than one charge/discharge cycle occurred each day. Also, if I read their runtime testing procedure in the product manual correctly, they discharge at a steady 75A rate until the voltage drops to 1.75VPC (Volts per Cell), which is less than 10% SoC,so a steady diet of discharges that deep is why the lifespan is so short (1.86 years if cycled daily).

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I'm not sure what the numbers (0 thru 25) at the right side of the graph mean. If EOCC means End of Charge Cycle and they charged to 2.58VPC (as stated on the right side vertical text) then it might indicate the the number of AH in the surface charge.

Also, might indicate the number of CCs of water added.

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Looks like the runtime starts at about 75% of rated value, climbs above 100 at about 100 cycles, peaks in the 300-400 cycle range, drops back to the spec line at aboput 600 cycle and dies suddenly before reaching 700 cycles.

That appears to contradict my belief that batteries progressively lose capacity over time.

I don't have access to a load tester that accurately tests the runtime of deep-cycle batteries, so for those that do, what kind of runtime (% of spec) is typically seen for batteries about two years old? (About 500 cycle if cart is used 5days/per week)

[JohnnieB]

Also found a similar chart in this Trojan Information video.
At about 2:02, but whole thing is interesting to watch.

http://www.youtube.com/watch?v=O-iWWo-abAU

http://www.youtube.com/watch?v=O-iWWo-abAU