Bulk charge cycle duration for Trace SW 4024

LagoonFarm

Hello all, I've been reading posts and would like some help. I haven't found any information that matches my problem. Here's my setup:

20 75W-BPSolar panels
Trace SW 4024 Inverter, made 1994
Ananda Power Systems PWC 200 with
Cruising Equip Meter 2+
Heliotrope PV Array charge controller
Tri-Metric Meter
12 305HT AGM Concorde batteries, 6 months old

My battery bank is down to about 50% and I've had trouble getting the bank up to 100% for several weeks.

On the inverter, my settings are:
Bulk Charge = 28.8
Float Voltage = 26.0
Absorption Time = 3 hrs
Charge Rate A = 10 A ac

Kubota 6500 W diesel generator, #8 wire from gen to inverter AC in, approx 60 feet away. Wire is connected to the 30 Amp 240V 4-prong twist lock receptacle.

With the batteries at 50%, I calculate I need to run the generator for 10 hrs at 45 A dc to bring the bank up to 100%, or 5 hrs if I charge at 90 A dc.

When I start a bulk charge, the Tri-Metric meter shows the DC amps that I expect, close to 5x what ever the Charge Rate is set on the inverter, less any active AC loads.

The bulk charge lasts only about two hours. It takes that long for the DC V of the bank to rise to 28.8, then the inverter goes to float and starts reducing current. Well that's only about 10% of the battery capacity put in during the bulk charge cycle. I've tried different charge rates and I get the same result. If use 20 A ac (100 A dc), then bulk cycle only lasts an hour.

I've adjusted the Float Voltage setting up and down to try and get the inverter to stay in bulk charge cycle longer.

How do I keep the inverter in bulk charge mode long enough to refill the batteries?

Thanks for any help.

Cariboocoot

Re: Bulk charge cycle duration for Trace SW 4024

Welcome to the forum!

So let's check the solar specs first, okay?
1500 Watts of panel in total.
915 Amp hours of battery in total. (305 AH 6 Volts, four in series for 24 Volts * 3 parallel banks)
Is this right?

There's your first problem: that battery bank wants 90 Amps of current which those panels can't supply. In fact they won't probably manage the minimum 5% current of 45 Amps. Maybe 40 Amps?

Second, when charging off the generator you seem to be missing the whole Absorb cycle. It shouldn't go from Bulk to Float; charging needs to stay in Absorb for as long as it took to get to 28.8 Volts or until the current drops to a small percentage (varies because of loads). Perhaps I'm misunderstanding?

Your charge cycle should look like this, regardless of source:

Bulk - high current (around 10% of the batteries' Amp hour rate) until Voltage reads 28.8
Absorb - 28.8 Volts at diminishing current for the time it took to bring batteries up to Absorb Voltage set point.
Float - Voltage drops back to 26, tries to maintain that level under fluctuating loads. (You could set this value higher too.)

Now there's a couple of other potential problems that come to mind. One is that the batteries are mis-wired and some are being left out of the loop. This could contribute to the batteries now being ruined due to chronic undercharging. That could be the case even if they're wired correctly

The other issue is that the venerable Trace SW inverter has failed. Unfortunately we are seeing a lot of this, and there really is no practical means of repair for them.

Ralph Day

Re: Bulk charge cycle duration for Trace SW 4024

My SW4048 will often act in the same way...you want a longer absorb and the unit will go to float before the timer has completed the cycle. If you're like me, you don't leave charging un-attended, so the easiest solution is to bump the float level up to the absorb level and monitor your SG (if those are FLA batteries) for the state of charge you want to achieve.

If your batteries are somewhat sulfated then the voltage levels acheived don't really reflect the SOC, it's the surface charge on the plates duping your readings. True SOC is reflected in specific gravity readings.

Best advice I can give: fuel up, put in some earplugs, check SG readings and wait.

Ralph

BB.

Re: Bulk charge cycle duration for Trace SW 4024

These are AGM batteries--so Specific Gravity can only be inferred by measuring the resting voltage (after several hours of no load/no charging).

Since these are Concorde AGM batteries, they can be "equalized" at 15.5 volts (31 volt for 24 volt bank) for up to 8 hours (read link). Do not do this with other brands of AGM without checking with the factory/documentation.

If the batteries are not getting warm, and it sounds like they are not getting fully charged, cranking up the charging voltage may not be a bad way to go (save time and fuel with the genset).

By the way, around 25.4 volts is the resting/fully charged battery voltage... 26 is (probably) still a surface charge and I would expect it to drop pretty quickly

-Bill

LagoonFarm

Re: Bulk charge cycle duration for Trace SW 4024

Thanks for the responses. I did use the wrong word in my description:

"The bulk charge lasts only about two hours. It takes that long for the DC V of the bank to rise to 28.8, then the inverter goes to float and starts reducing current." I should have said, "... inverter goes into absorption..."

The absorption cycle does start reducing current when the bank gets to 28.8.

The problem is the duration of the bulk cycle is not long enough to get the battery bank close to full charge. The bank gets up to 28.8 V too fast.

At 45 A dc rate the bulk cycle lasts about 2 hr, then absorption at around 25 A dc for 3 hrs. That's only 90 + 75 Ahr = 165 Ahr put in to the bank. I need 450+ Ahr when I charge using the generator. At 90 A dc rate the bulk cycle lasts 1 hr and then absorption starts. Either way, the net resulting Ahr is the same.

The batteries are wired correctly. These are sealed AGM so I can't check SG.

If the 4024 is functioning correctly, then will the bulk cycle last much longer at 90 A dc, perhaps 4 or 5 hours? Then absorption for 3-4 hrs at 25 A dc would work.

Regarding the PV array, I can get 40 A dc. Do I need to increase the array size to 3500 W or so?

Thanks!

Cariboocoot

Re: Bulk charge cycle duration for Trace SW 4024

Okay, the Bulk stage lasts s long as it needs to: it puts as much Amperage to the batteries as is available until they reach the Absorb set point. Most of the mp hours are "replaced" during the Absorb cycle. The things that will shorten Bulk time are very low Amp hour usage or very high current rate (which can be a real problem for the batteries). You don't seem to have high current, so either you're not using much Amp hours or ... the batteries are losing capacity.

Unfortunately you can't do straightforward calculations on battery charging due to the Peukert effect. It isn't as simple as 'X' Amps over 'Y' hours = 'XY' Amp hours used/stored. The 'X' will vary over the 'Y', and the last few Amp hours take longer to replace than the first many.

I'm going to suggest you follow Ralph Day's plan and push the Float Voltage up to Absorb level, watch it very carefully until the Trimetric says it is fully charged (look out for batteries getting too warm or any signs of case expansion/gassing). Then let them sit unused over night and check the resting Voltage. This keeps looking like a case of batteries that may be dying or dead.

Dave Angelini

Re: Bulk charge cycle duration for Trace SW 4024

In the SW charge menu there is a setting called end amps or some other similar wording. It must be set to zero to get the full absorption time. Since I think these are AGM's you need to accuarately monitor that you are getting the minimum amount of amps that whoever made your batteries reccomends.

Ralph Day

Re: Bulk charge cycle duration for Trace SW 4024

Dave,
I think you're confusing SW with MX manuals. There's no end amps on the charging parameters with my SW4048 inverter, but there is and ''end amps'' setable selection on the MX60 charge controller.

End amps would be nice on the SW though.

Ralph

RCinFLA

Re: Bulk charge cycle duration for Trace SW 4024

SWplus units have termination of absorb charging phase based on current drop off capability but not regular SW's. They are solely based on timer setting.

If you are only getting two hours in absorb then it is because you have timer set to 120 minutes. From 50% SOC it should take a while for batteries to reach absorb voltage in bulk current phase.

SW bulk current regulation is based only on AC input amps, not D.C. Best way to figure DC amps on battery is (AC power input X inverter efficiency loss)/Battery voltage. This means the battery DC current will taper off somewhat as the battery voltage rises during charging.

Lets say you start out at max input power capability of SW4024 of 4000 watts (33 amps of AC Chgr Current). Efficiency at this power is about 87% so you get 4000 X 0.87 = 3480 watts to batteries. When first starting charge, with batteries at 24.5 vdc you will get 3480w/24.5v = 142 amps D.C. When battery voltage gets close to absorb voltage, say 28.6 vdc, then the bulk charge current will have dropped to 3480w/28.6v = 122 amps. (SWplus manual has efficiency curves which are same as regular SW)

You can do max charge rate with your generator and battery AH capacity, especially with AGM's. Just watch for too much current imbalance between parallel sets of batteries. Don't worry about reserving gen power for ACout loads, as the inverter will automatically back off on charging to stay within ACin max setting limit if ACout load requires more power. I would not worry about pulling 33 amps on single 120v leg of generator unless gen breaker trips. You should be able to single side 120 vac load to at least 30 amps unless you are also running 240 vac loads directly off gen. If there is 120v/240v switch to give full gen power to 120vac load, then all the better.

The SW's actually starts additional cut back on bulk current a little before absorb voltage setting is reached.

Your absorb level is too low for generator operation (unless you want to burn more fuel). The absorb time is somewhat interactive to bulk current rate. The higher the bulk current, the less the battery SOC will be at absorb voltage for same absorb voltage setting. Peukert's effect for charging. AGM are better.

You can also have issue with absorb voltage being reached to quickly as batteries age, due to their series resistance going up with age.

LagoonFarm

Re: Bulk charge cycle duration for Trace SW 4024

Cariboocoot wrote: »

Okay, the Bulk stage lasts s long as it needs to: it puts as much Amperage to the batteries as is available until they reach the Absorb set point.

<snip>

This keeps looking like a case of batteries that may be dying or dead.

If you had my equipment (Trace 4024), and 6-month old AGM batteries (12 of the 305HT Concordes, 3 groups for 24V, 915 AH capacity), then how long would you expect the bulk cycle to last, when you start genset charging with battery voltage at 24.4V?

Thanks

RCinFLA

Re: Bulk charge cycle duration for Trace SW 4024

The 24.4 vdc does not really tell much about state of charge unless it is a number after a couple of hours of no load or charging.

Lets just say they are at 60% SOC and you are running 20 amps AC for charger setting on SW4024. You need to replace 40% of 915 AH or 366 AH's.

You are getting 20A x 120vac = 2400 watts, x 0.95 = 2280 watts into batteries.

I would expect the battery voltage to jump up a bit as soon as charge current is applied. Starting at 24.6 vdc that would give 2280w / 24.6vdc = 93 amps into batteries. At absorb voltage of 28.8 vdc the bulk current would be 2280w / 28.8vdc = 79 amps. Assume a linear drop off between these two points then average bulk charge current is 86 amps.

At 10% AH rate of charge the batteries will be at about 88% SOC when absorb voltage is reached at 28.8 vdc. 88% - 60% = 28% of AH's is replace during bulk phase. This is 28% of 915 AH or 256 AH. Charging efficiency on battery for bulk phase is about 92%, so bulk phase AH input is about 256 AH/ 0.92 = 278 AH's. At 86 amps DC average this would make bulk phase last about 278 AH / 86 A = 3.2 hours.

If it take less time then battery is probably at higher initial SOC. How sure are you of voltage measurement accuracy? Just the 18 watts of idling inverter will drop battery voltage a little.

LagoonFarm

Re: Bulk charge cycle duration for Trace SW 4024

RCinFLA wrote: »

The 24.4 vdc does not really tell much about state of charge unless it is a number after a couple of hours of no load or charging.

Lets just say they are at 60% SOC and you are running 20 amps AC for charger setting on SW4024. You need to replace 40% of 915 AH or 366 AH's.
<snip>
At 86 amps DC average this would make bulk phase last about 278 AH / 86 A = 3.2 hours.

If it take less time then battery is probably at higher initial SOC. How sure are you of voltage measurement accuracy? Just the 18 watts of idling inverter will drop battery voltage a little.

Thanks for the numbers and the scenario. I'm basing the voltage after the system has been *almost* at rest for 8 hours (I shut loads off at the service panel at 10 PM and check the system at 6 AM next morning). The only load during the night is the inverter.

You are indicating the bulk charge cycle should last about 3.2 hrs. Then the rest of the needed charging (366 Ahr - 278 Ahr = 88 Ahr) would come through the absorption phase. The absorption should take about 4-5 hrs, right?

These AGMs can take 31.0 volts for up to 8 hrs for an equalize conditioning.

I ran the gen yesterday and followed one poster's advice to bump the bulk voltage setting to an equalize voltage level. I set the bulk voltage setting to 30.5 V and had the AC amp charge rate at 25.

The Tri-Metric showed 88 A dc coming in. This lasted about 1 hour, then over the next 30 minutes, the Tri-Metric showed amps going down to 45 A dc with voltage at 30.x. An hour later the Tri-Metric showed 35 A dc. I let the gen run for another 4 hours, amps continued down to 15. About 30 minutes later it went into float and I shut the system down.

If I should expect the bulk phase (avg 85 A dc) to last 3+ hours, but it only last 1 hr, what do I do to determine if the problem is with my batteries (nearly new) or the inverter (very old)?

Thanks. Your posts are helping me understand a lot.

RCinFLA

Re: Bulk charge cycle duration for Trace SW 4024

I don't think you have a problem. The batteries are just not as discharged as you think. The Trimetric will say anything you set it for. There are voltage calibration, AH, and charge efficiency settings.

I would not run the generator to accomplish the absorb phase unless you have not had enough sun for several days. It is very inefficient on fuel consumption to do absorb time on a generator since the generator is lightly loaded.

AGM's absorb charge well (good recharge efficiency).

When recharging from generator push as much current as you can, up to a max. of 25% AH (or 85% loading on generator) during bulk current phase. Raise the absorb trip point voltage to 30 vdc. Forget about doing absorb phase. If batteries have not been fully recharged for several days THEN do a 2-3 hour absorb cycle.