[meanderingthemaze]

Alright, so I just got off the phone with two different companies with two different conclusions, and of course, they both claim to know what they are talking about.

High Performance Golf Carts that produce the AC-50 motor (w/ Curtis AC 1238-75) says the recommended Lead Acid voltage be 96V, because the final voltage will be around 126V. The limitation, they say, is the Curtis controller which has a cutoff voltage of 130V DC. If you do Lion, they say, you can go up to 108 because the final charge is also around 126V. Fine.

So, I call the US Battery rep who is selling Lead Acid and he says that I can use up to 108V Lead Acid. That the final charging voltage will be around 126V. He says he's been in the business for 40 years and is sure of this.

So, I call back the motor company and they say that it all depends on the weather. Temperature dictates the final voltage of Lead Acid. He was adamant that I would have problems if I used more than 96V Lead Acid.

So, who to trust, the guy who sells the system and has already made working vehicles with Lead Acid? Or the battery guy who's been doing this forever? Or is there a way to find an answer independent of these two.

If not, I guess I should accept the motor company's answer as they have no interest to sell more or less Lead Acid batteries. And they have real world experience with their systems. And they happen to run their systems about 30 miles away from me in basically the same weather.

Any help from the forum on this one?

[ewdysar]

It seems like this is more dependant on the type of L/A battery and the charging profile being used. At an acceptance voltage of 14.4V/battery, you've barely got room for 9 batteries (14.4V x 9 = 129.6V). My 12V "Smart charger" runs flooded cells to 14.9 - 15.0V, AGM to 14.5V, and Gels to 14.1V.

Backing into your numbers, 126V/9 batteries = 14.0V/battery or 2.33V/cell. Your batteries will probably not get "full" at those voltages.

IMHO, with an absolute limit in your system of 130V and L/A batteries, you're better off with a pack with 96V nominal. Even with TS LiFePO4, your best bet would be 34 cells giving a max charge voltage of 124.1V (3.65V/cell), though I charge mine to 3.8V/cell with shunting or 129.2V in this scenario.

I hope this helps...

Eric

[meanderingthemaze]

Thanks it helps a little. I guess I'm a little confused about how apparently complex lead acid is, in that, there is still controversy over how they act and what they need according to what I read. Perhaps this is because there are so many varieties out there with slightly diff needs?

For the record, I'm planning 16 x 6Vs. So each battery should have an open circuit voltage of what, 6.3V nominal right? But in charging, it goes higher during the saturation phase right? But the big question is how high will they go. They then return to a lower voltage for final charging. But where does that end up?

Using your numbers, I guess a 6V would be at highest half of 14.4V or 7.2V. Then taking controller cutoff voltage of 130V/7.2V = 18.06 batteries. Or 7.2V x 18 bats = 129.6V right?

So, 18 batteries or 108V should work right?

Well, again, the motor guy said that it depends on weather. He said I would have nothing but problems. What to do?

[ewdysar]

Maybe this will help. L/A batteries are 2V nominal per cell, 6V = 3 cells, 8V = 4 cells and 12V = 6 cells. Look up some of your prospective chargers and see what they recommend in their charging profiles, most chargers limit AGM batteries to 2.4V/cell and flooded cells around 2.5V/cell. If your charger really limits the voltage to 2.4V/cell (129.6V total), then you probably won't kick the controller over its limit. but it really depends on your charger.

Eric

[meanderingthemaze]

That's the first time I've heard that it depends on the charger. Don't lead acids have a specific point they need to reach in charging in order for longevity regardless of what's charging them?

The battery guy brought up that they shouldn't go over a particular specific gravity level to prevent overcharging. It seems that the Zivan is a pretty trusted charger. I was told that it could be programmed to do whatever you tell it to do. But I'll take a look at the recommendations as you suggested.

I do appreciate the input Eric, thanks.

[ewdysar]

Yes, the battery does define the recommended charging current (voltage and amps) but the charger has complete control. Charging too low will not use the battery's manufactured capability and eventually lead to a loss of capacity. Likewise charging too slow can lead to premature loss of cycles (lifespan). Charging too high or fast can overheat the battery and kill it slowly (or not so slowly). So get the charging specs from the battery manufacturer and match the charging profile to those specs for the best performance and lifespan. As you will see, the specs are typically listed as ranges rather than really precise numbers which means that you have some leeway in tailoring the system to your installation, I wouldn't recommend operating right at the limits (high or low) because it doesn't give you much room for error.

Do some searches on charging profiles, equalization and desulfation, I think that it helps to get a variety of opinions and figure out what makes sense to you.

Good planning (don't count on luck) in your project,
Eric

[rmay635703]

Originally Posted by meanderingthemaze

That's the first time I've heard that it depends on the charger. Don't lead acids have a specific point they need to reach in charging in order for longevity regardless of what's charging them?

The battery guy brought up that they shouldn't go over a particular specific gravity level to prevent overcharging. It seems that the Zivan is a pretty trusted charger. I was told that it could be programmed to do whatever you tell it to do. But I'll take a look at the recommendations as you suggested.

I do appreciate the input Eric, thanks.

Ideally you put them on a schedule of light (but full) charges coupled with an occasional equalizing charge, how high you charge depends on how much you discharge. The more you discharge the more you overcharge to try and remove sulphation.

A FLA battery can be fully charged albeit very slowly by rather low charge voltages and rates.

It depends on the condition of the battery and how it is used.

Good Luck

[meanderingthemaze]

Likewise charging too slow can lead to premature loss of cycles (lifespan)

It's interesting that you mention charging too slow can lead to loss of cycles because I was considering putting solar panels on the bed of the truck, but someone was saying how they had an issue with it prematurely killing their pack. It seems counter-intuitive because usually lead acids like trickle charging, but perhaps trickle charging daily could over time be bad for them?

thanks to you both

[rmay635703]

Originally Posted by meanderingthemaze

It's interesting that you mention charging too slow can lead to loss of cycles because I was considering putting solar panels on the bed of the truck, but someone was saying how they had an issue with it prematurely killing their pack. It seems counter-intuitive because usually lead acids like trickle charging, but perhaps trickle charging daily could over time be bad for them?

thanks to you both

Charging too slow is always better than not charging at all, I believe I should qualify what I mean by light, a light charge is independant of rate but goes to a lower finishing voltage but for a longer time (at least thats how I use it)

The other guy talking about charging too slowly is refering to if you ALWAYS charge slowly (low amps throughout) and never hook the thing up to a faster normal charger, your battery pack will sit at a low SOC for a longer time in this scenario.

However your idea of solar charging while out and about, then assumably charging in a NORMAL way is much much different than what I believe he meant.

Any time your battery sits at a low SOC it sulphates rapidly and ages, any time you apply a charging current, even a very small one the rate of sulphation is reduced greatly and your pack will not age as quickly. However you would still want to do a normal charge because your pack still sulphates much quicker, even under charge at a low SOC, your big charger will bring the pack up to the correct SOC levels quickly and blow off sulphation.

I believe the reason some folks kill their pack with solar is that either
1. They as the other OP said charge too slowly all the time taking days to top off the pack
2. Overcharge, AKA the panels never shut off and fry your batteries while the car sits fully charged.

A good charge controller and common sense should prevent either.

Cheers
Ryan

[MN Driver]

I read this thread and then reread the original post and have a question. Is this question specifically only about lead-acid cells or about using 108 volts with the Curtis 1238-7501 and AC50 combo?

If the question is about the latter, then the 96 volts will allow for higher regen current which will run the voltages higher in those cells in the short term than what will normally be seen with a lower current charge, spiking them into their equalizing voltage range if they aren't already at a lower state of charge. I'm not quite sure how suitable regen is to lead acid, especially getting up in the 100 amp regen range, you wouldn't want to do this with any cell that can't handle gassing voltages such as a gel battery.

Without regen, or regen dialed down appropriately 108 volts will be fine because there is no way that by the time you've shut off your charger and turned the power to the controller on that it will be over the 130 volt shutdown point.

You would need to know the dynamics of your batteries to determine whether or not regen will be efficient, whether the batteries you choose can handle it, and whether or not your voltage will shoot past 130volts and what maximums you will need to program into the Curtis to avoid battery damage or controller cutout.

...if this was only a question about the lead-acids, I'll step aside with my answer but it seems to me the root of the question was more about the Curtis in which charging voltage is a very different beast than regen voltages over a wide variety of SOC points and higher amperages.