concurrent CC and generator charging

jtdiesel65 · January 2012

According to the bogart the generator will put out ~125a via an sw4024. I have two charge controllers that will put out some amount of amperage each. I was fiddling around trying to get the total amount of charge current to be max generator plus the CC output current. But what I see is what appears to be the CC's pushing up the voltage which causes the sw4024 to throttle current to partial output. So I would see ~10a from each charge controller and only ~70a from the generator. This seems to be more than just the result of the change in (total watts available)/(bat volts) as voltage rises.

We've been in a "no sun for three weeks going on four" cloud cover pattern. I think I've been hovering in the 75-90% battery. There haven't been significant loads of sufficient discharge for the sw4024 to auto start the generator. Is there anyway to trick the system to do a different amps vs volts curve? It would seem that possibly even at 50% battery, I wouldn't be able to leverage all 3 sources for their max amperage.

mike95490 · January 2012

Re: concurrent CC and generator charging

Surely there is a way to manually start the genset and let it run ? If you can - fire it up at dawn, and let it bulk charge the batteries, and by 10, the sun may be enough to finish them ??

vtmaps · January 2012

Re: concurrent CC and generator charging

jtdiesel65 wrote: »

trying to get the total amount of charge current to be max generator plus the CC output current.

During bulk stage the charging currents can be nearly additive. Once you get to or near your absorb voltage, the charging currents will not be additive.

mike90045 wrote:

If you can - fire it up at dawn, and let it bulk charge the batteries, and by 10, the sun may be enough to finish them

mike90045 has the right idea. You don't need more charging amps, you need more charging time. Its also better for the batteries not to push very high currents into them.
--vtMaps

Vic · January 2012

Re: concurrent CC and generator charging

Think that your battery is too fully charged to accept more current at the charge voltage you have set.

When batteries are mostly charged, and mostly discharged, the impedance is higher than when in center portion of the charged curve.

Unless you jack up the charge voltage settings, on a mostly charged battery, you should notice that in the beginning of an attempt to do high rate charging, that the high current portion of the charge cycle is short, as the battery quickly rises to the Asorb target, and the current quickly begins to taper off.

This will happen with any charge source that has sufficeint current output capability.

If you are trying to balance multiple chargers, such that the PV is the dominant source, and the genset is secondary, you could try setting the CCs to a bit higher charge V than that of the SW charger, but multiple sources each have their own regulation behaviors, and you could find that these multiple feedback loops work against each other many times.
EDIT: Forgot to mention that if you are trying to make the CCs the dominant cource of chargte current, that the Charger AC current can be backed down to reduce the contribution from the genset.

The SW series of inverters are very stout, but the way that they regulate charge voltage, with other charge sources combined is sometimes disappointing.

EDIT: While opinions differ regarding doing SOME charging at high rates (C/10), I do go out of my way to so, occasionally, as it is recommended by the supplier of most of the batteries in my universe -- Surrette. This is recommended to keep active plate material exposed to electrolyte .. ie, maintain Charge Acceptance over an extended time. Some here, do not buy into this -- I do. We all are entitled to our opinions, and they are just that - opinions.

Vic

jtdiesel65 · January 2012

Re: concurrent CC and generator charging

I was thinking that the only reason I was seeing 70a was because the charger on the sw4024 was limiting as a percent of total input based upon battery voltage. Using the same curve, if I had a bigger generator and the sw4024 had a more capable charger, I might have seen more than 70a. I was also wondering about the c/10 amperage and having a battery that is only cycled down ~20%. The charging sources would only let the battery see a c/10 amperage for brief few seconds as battery voltage rises.

But in addition to all that I'm wondering if I'm getting the most out of the generator. It's a Kohler 8.5rmy. The most I've seen on the Bogart meter is ~125a, which even at 28.8 is only 3600w. The rating is 8.5RMY120/240 VAC standby ratings 29-35 amp. I suppose that might be one leg 120*35 = 4200. 240*35=8400.

jtdiesel65 · January 2012

Re: concurrent CC and generator charging

well, the stator is wired for 120v. So it should put out 70a @120. It's the sw4024 charger that is limiting it. Interestingly buried in the sw manual is a couple paragraphs on charging with multiple inverters. It basically says, the sources will be close to additive with a discharged battery, but they actually never will be due to the voltage readings. That's what I'm seeing except that the other chargers are classics, not additional sw's.

mike95490 · January 2012

Re: concurrent CC and generator charging

Depending on the wire gauge from the charger to the battery, you may be seeing voltage build up from the wire's internal resistance (.01 ohm @ 50A = .5V) - do each charge source have their own run to the batteries, or do they share a common cable ?

Or it may be just goofy gear.

jtdiesel65 · January 2012

Re: concurrent CC and generator charging

well, they are all connected to a 250a disconnect which is connected with 4-0 copper to the battery. It seems to be just the way the sw charger works. I don't really see much of drop of output on the CC's (although there isn't much sun either). The drop seems to only be in the sw.

It would be nice to get more out of the generator. As it stands it will never run at more than at 1/2 load because the sw doesn't have capacity. Sounds like what I need is another sw.

Vic · January 2012

Re: concurrent CC and generator charging

jt,

Well, are you monitoring the battery voltage when you feel that there is insufficient charge current from the SW?. If the battery voltage approaches the Asorb target voltage, the SW will taper the charge current. BTW, on my SW+es, the charger voltage often seems to NOT be temp compensated.

Do not have my SW+ manuals here, but in the charger menu, there is a setting for AC input Amp limit for the charger. This is AC current at 120 VAC. Make certain that this is set high enough to allow the SW to run as high as the max available from the genset and SW. But, if the battery voltage is near/above Asorb voltage setting, the SW current will taper.

Think that you may be trying to allow the CCs to provide max current from PV, and have the genset make up the rest. BUT if you are looking to do high rate charging of the battery bank, you may need to discharge the bank to a lower SOC, in order to keep the SW's charge current from raising the batt voltage to a point where the SW is tapering, as it is near Vabsorb. On my systems, charging at 100 amps or so, the battery voltage gets dragged up by about 2.5 volts from the charge current. This is when the lightly loaded battery voltage is about 52 - 53ish V, before charging (know that UR system is 24 V). If I want very much time spent at high charge currents, need to discharge the bank voltage into the high 40's (under light loads) to be able to spend 45 mins or an hour at high rate.

I may not know just what you are wanting to do ... Vic

RCinFLA · January 2012

Re: concurrent CC and generator charging

The SW4028 will throttle back as it approaches bulk voltage setting. Same thing if it is in float mode.

Depending on what rev of software you have you need to be careful about how much to PV current is pushing to batteries as battery approaches absorb (bulk named on SW) voltage is approached. Older SW4024 will actually push excess power back at genertor.

Realize the SW regulates charging based on AC current and battery voltage. As battery voltage rises the average DC current to batteries reduces.
Most accurate why to figure battery current is to figure input AC power based on Charger AC current max setting x 120vac. Then factor in inverter efficiency, 0.88 to 0.94 depending on power level pushed. This is power delivered to battery equals battery voltage x battery current. The lower the battery voltage to higher the DC current.

SW inverters have no direct measurement of battery current.

Vic · January 2012

Re: concurrent CC and generator charging

Hi RC,

Thanks for correcting my nomenclature. The Asorb target voltage in the SWs is the "Bulk" voltage setting.

My SW+es are late units, altho, I do not the FW rev level. I do see the situation where the SW+ drags the AC input voltage out of qualification when using Inverter gensets, unless the AC charger input current is dialed back to about 50% of the genset's capability. Larger, conventional genssets are not disturbed (one 18 KW, and the other 25 KVA).

Thanks again RC and good luck, jt. Vic

jtdiesel65 · January 2012

Re: concurrent CC and generator charging

Vic,

Yeah I was trying to do a higher rate for at least a short period anyway, but the sw charger wasn't allowing me to do it. Part of the problem is I put in a new battery in late Nov. and we haven't had much for sun in since. At any rate SG doesn't jive with voltage. Voltage seems to be higher than what SG would indicate. So SG says battery is actually lower than volts would indicate. I think it was 1.235-1.24 but 25.2v at rest.

What I was hoping for was some way to trick the sw to think it had a larger genset attached to it. It's charging curve looks like it's fixed at a 24v starting point. So with a ~4000w input it only puts out ~70a/25.5v, rather than starting at ~120a/25.5v and tapering down to absorb voltage. I was hoping for some way to keep it at ~120a for a short period.

Interestingly today, there was a brief period of where I did see ~180a combined from the generator. SG was ~1.225 and v was 24.8 with a ~5a/24v load. SG would seem to correspond to something near 50% discharge. Although that seems a bit odd since ~8kwh went into the battery yesterday and we only use about 3/day.

concurrent CC and generator charging

Comments

Categories