New US1800XC batteries - > 100% SOC after resting?

[rlw]

Hey all,

It's been a while since I posted here. I put a new set of US1800XC batteries in my '84 Marathon a couple of weeks ago. Got 'em locally for $90 a pop. I could have saved $10/battery ($80 a pop), but I'd have eaten that up in gas and time picking them up. This cart rarely goes more than a couple of miles a day, so I didn't see the need to get Trojans for another $150 for the set.

Charged 'em with my ancient "white" Textron ferro-resonant (not-so) dumb charger. Set the timer to 4 hours, voltage before charging was 37.7V (about 88% SOC - according to this table). After charging (and overnight) it was up to 37.9V - about 90% SOC. Each night, the rest of the week, I'd charge it for 4 hours. I ran the cart pretty heavily for me (probably 3 or 4 miles, total) over the Labor Day weekend, and before I put it on the charger, it was down to 36.5V (around 55% SOC). Another 4 hour charge, and the next morning I was at 38.5V, which seems to equate to about 109% SOC.

Usually, I put the cart to bed around 9 PM or so, set the timer on the charger to 4 hours, then get the cart out later the next day. I've been consistently seeing > 100% SOC. From reading the discussions about batteries, the US1800XCs aren't the best batteries out there, in the collective opinion of the forum. Am I checking the after-charge voltage too soon, and the batteries haven't rested by then?

Just wondering - hoping JohnnieB will chime in - he's the go-to guy when it comes to charging batteries (or ANYTHING about batteries in general). I've read JohnnieB and ScottyB's posts about "charging the hell out of 'em to break 'em in, but was a little skittish about over charging them by putting the charger on for the full 12 hours. By the way, I still haven't seen any indication of acid coming out of the vents and the cables and posts are clean as a whistle.

RLW

[Sir Nuke]

you should let them REST for 12 hrs after a charge before checking them for SOC.

[JohnnieB]

First of all, there isn't anything wrong with the US 1800XC. It is a quality product, but it is only 208AH, so it's storage capacity is less than the standard 6V battery (225AH) used in golf carts, and in most golf cart applications the higher the Amp-Hours, the better.

Considering the cart is basically stock and distance traveled is modest, they were a good choice, or at least an acceptable one. Unlike many cart owners, your battery pack isn't undersized for what you are asking the cart to do. It also sounds like you are taking care of the well, so they ought to last to a ripe old age.

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If you put the batteries on charge for 4-hr, starting at 9PM, anytime after 1PM the next day will give you a good voltage reading for estimating SoC.

However, I suspect you are undercharging your batteries. (New batteries typically read higher than 100% on the charts)
Deep-cycle batteries made by US Battery need to be charged to higher On-Charge voltage than Trojan batteries and your charger is was designed with Trojan batteries in mind. Fortunately it is a manual type (Timer only), so it might be okay.

Letting your charge run for 12 hours won't hurt your batteries. In fact, a few 12 hour charges are probably needed to get them up to where they ought to be.
Attached is the Single Stage (ferroresonant) charger specs from US Battery.

If you have a DVM that has a Min/Max or Peak hold function, use it to determine what the max On-Charge voltage is reached during a 12 hour charge cycle.
Or, put the batteries on a 12 hour charge at 9PM as usual and measure the On-Charge voltage just before 9AM the next day.

If it is less than 46V, you are undercharging your batteries.

[rlw]

JohnnieB,

Thanks for the info. As I recall, you and I had a pretty good discussion quite some time ago when the diodes shorted on my charger. You explained that it was a pretty elegant design, in that it acted like a "smart" charger, even though it consisted of a capacitor, ferro-resonant xfrmr and a couple of diodes.

I'll give 'em a 12 hour charge and see what the voltage is at the end.

Thanks again,

RLW

[rlw]

I spent this evening installing my 4 digit voltmeter. It's been charging now for about 15 minutes. I'm running at 45.28 volts and about 4 amps. I'll check it in the morning and see if I break the 46 volt barrier.

[rlw]

Charged overnight on Friday the 13th for 12 hours. Checked voltage on Saturday morning (about 11.5 hours into the charge) and I cracked the 46V barrier (46.05V to be sort of exact). Charger ammeter was reading around 2 to 3 amps.

I didn't write down the voltage after the cart rested for almost 12 hours (slaps forehead!), but I recall it being MORE than 38.2V. Still > 100% SOC AFTER resting.

Drove the cart for about a mile-and-a-half Saturday evening and parked it outside, not connected to the charger. Turned on the meter this morning before moving the cart, and the voltage read 38.21V (close enough to 100% SOC for the girls I go out with). That's AFTER the 1.5 mile trip yesterday.

Looks like my charger can run at 46V, and it looks like I'm getting a full charge. I'm still a tad concerned about overcharging. BTW, the battery tops are still clear of any acid/water after charging.

Any advice/suggestions will be greatly appreciated.

RLW

[JohnnieB]

Originally Posted by rlw

I spent this evening installing my 4 digit voltmeter. It's been charging now for about 15 minutes. I'm running at 45.28 volts and about 4 amps. I'll check it in the morning and see if I break the 46 volt barrier.

What Make/Model meter?
Picture would be nice.

Originally Posted by rlw

Charged overnight on Friday the 13th for 12 hours. Checked voltage on Saturday morning (about 11.5 hours into the charge) and I cracked the 46V barrier (46.05V to be sort of exact). Charger ammeter was reading around 2 to 3 amps.

I didn't write down the voltage after the cart rested for almost 12 hours (slaps forehead!), but I recall it being MORE than 38.2V. Still > 100% SOC AFTER resting.

Drove the cart for about a mile-and-a-half Saturday evening and parked it outside, not connected to the charger. Turned on the meter this morning before moving the cart, and the voltage read 38.21V (close enough to 100% SOC for the girls I go out with). That's AFTER the 1.5 mile trip yesterday.

Looks like my charger can run at 46V, and it looks like I'm getting a full charge. I'm still a tad concerned about overcharging. BTW, the battery tops are still clear of any acid/water after charging.

Any advice/suggestions will be greatly appreciated.

RLW

You really shouldn't let your batteries sit overnight in a partially discharged state.
If you use the cart any at all during the day, it should go on charge that night.
Also, if your cart sits for a week without being used, it should receive a charge.

This is because your batteries begin to self-discharge the moment the charger shuts off and deep-cycle lead-acid wet-cell batteries typically self-discharge at about 1% per day, so the would be down to 93% SoC in a week.
The plates start sulfating really fast when the sit for any length of time at 70% SoC or less, which is about a month, but some sulfation still occurs at higher SoC levels and should be avoided if possible and practical.

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Many battery manufacturers and vendors caution about overcharging, but none define what overcharging is, so overcharging concerns commonly exist when overcharging issues rarely do.

A lead-acid cart battery isn't fully charged until the specific gravity of the electrolyte ceases to increase while a charging current is passing through it. The voltage tracks the specific gravity (SG + 0.845 = Voltage) so it also ceases to increase when the battery is fully charge. Overcharging occurs when the specific gravity of the electrolyte ceases to increase and the charging current continues to flow through the cell at a rate that is higher then the self-discharge rate of the cell, which is about 1% of the AH rating at the 20 hour rate for the battery.

Since the charger's output drops into to the 2-3 amp range as the On-Charge voltage approaches 46V, and you have 208AH batteries, the chargers output barely exceeds the battery's self-discharge rate, so it would be next to impossible to overcharge those batteries with that charger no matter how long you let it run.

To overcharge your batteries with a ferroresonant transformer type charger whose On-Charge voltage maxes out just over 46V, you would have to watch the charger's ammeter and initiate a new charge cycle every time the ammeter dropped below 20A, and keep doing it for a day or more.

It can be done, but it would have to be deliberately and intentionally done.

-------
You are using a SoC chart for "mature" Trojan batteries and have "new" batteries made by US Battery.

New batteries have a slightly higher At-Rest voltage and US Battery batteries have a slightly higher At-Rest voltage at 100% Soc than Trojan batteries.

I received SoC vs voltage data from US Battery (Attached) a few days ago and made a chart with it. (also attached)
Except for 100% SoC, there isn't much difference between Trojan and US Battery data.

[rlw]

JohnnieB,

Thanks (again!) for all the info.

You really shouldn't let your batteries sit overnight in a partially discharged state.

Yeah, I know that - I usually do park it in the garage and throw it on the charger, just didn't do that last night - 'twas a long, tiring day. Should I put it on the whole overnight 12 hour charge every night, or pick a shorter timer setting, like 6 hours? 'Til I hear different, I'll stick to the 12 hour nightly charge.

Doing a little math (and a little guessing), figuring a 75% efficiency between the wall socket and the charger plug... If I'm charging at 36V and an average of 4 amps every night (over the whole 12 hours), that's (12 hours x 144 Watts)/.75, or 2.304 kWh a night - around here a kWh costs about a dime, so I'm looking at about a quarter a night to keep this thing topped up. I think I can afford that!

Somewhere in my junk pile, there's an old kWh meter my dad left me - maybe I'll wire it up between the wall outlet and the charger and get a real idea how much it costs me to charge this thing every night. I don't want to be responsible for Don Blankenship's heirs ripping the top off the hill behind your house just so I can keep my batteries up to snuff!

Since the charger's output drops into to the 2-3 amp range as the On-Charge voltage approaches 46V, and you have 208AH batteries, the chargers output barely exceeds the battery's self-discharge rate, so it would be next to impossible to overcharge those batteries with that charger no matter how long you let it run.

That's why I wanted to wait for your comment -- you always give clear and helpful info. I'm gonna stop worrying about overcharging them.

Thanks again,

RLW

[rlw]

Originally Posted by JohnnieB

What Make/Model meter?
Picture would be nice.

I got it about a year ago from a Chinese seller on eBay. I spent the magnificent sum of $8.00 on it (with free shipping on - literally - a slowboat from China), and now I see that it costs $6.99 with free slowboat shipping.

Click here for the link from eBay.

I tried to take a photo of it, but it refreshes its display every 300ms, so not all of the numbers were lit in the image. It's a 4 digit, 0-199V, auto-decimal, red LED, 3 wire meter. One common ground, one 12v power source, and one line for the test voltage. I had some old plenum-rated 3 pair 24 gauge cable I used to hook it up. Found some old hard disk 4 pin Molex power connectors (both male AND female) in the junk box (it's more like a junk BASEMENT than just a mere BOX). Soldered the wires from the meter to a female connector (meter red to connector red, meter black to connector black, and meter green to connector yellow). Had another 4 wire male-female disk drive power splitter, so I cut the black wire and soldered in a toggle switch (to turn the meter off and on), then soldered a male connector on the end of the plenum cable, where I doubled up green/white-green, orange/white-orange, and blue/white-blue wires. Hooked the battery side up under the seat, and now have a panel meter on the "dashboard".

RLW