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Trying to Figure something out!
By radiantboy, Section Controls Posted on Sat May 20, 2006 at 12:22:54 PM MST
Question about surge and battery size

I have a question relating to surge and battery amp/hour ratings. This is my experience: I have two solar systems (actually I have more, but I'm keeping this as simple as possible). One system has a 100 amp/hour battery (MK brand gel) and the other a 200 amp/hour battery(Universal Battery AGM). Both of these systems use the "el cheapo" Vantec brand modified square wave inverters. The 100 amp hour battery is connected to a Vantec 750 watt inverter, and the 200 amp hour battery is connected to a 1500 watt Vantec inverter. (I am not including info about the solar panels on these two separate systems, since for the purpose, they would be irrelevant since this situation that I describe has been done repeatedly at night. Of course, both batteries were at full charge). I'm trying to run my television, a 27 inch Sony. Using the grid to run the TV, I have measured (at startup ,according to my kil-o-watt meter) around 600-700 watts pull for a few seconds (the surge), but then this quickly drops to a continuous 90-100 watts for the remainder of time. Now -- here's the mystery. When I try to run my television (the 27 inch Sony) with the 200 amp hour AGM battery/1500 watt inverter combo, it is unable to handle the surge. What happens is the TV turns on, then immediately cuts off, then "tries again" over and over again with the same result, until I disconnect the inverter. (When I use this sytem with my computer monitor, it also cuts on and off, but after about four or five tries the monitor then comes on and stays on. In fact, right now, it is running my computer monitor.) What is apparently happening is that the initial surge lowers the battery voltage so quickly and greatly that the inverter cannot run anymore and cuts off. In the case of the computer monitor, this isn't absolute, since the monitor has a smaller surge. But when I use the smaller 100 amp hour gel battery/750 watt inverter (with the Sony TV), it handles the surge without a problem. The TV starts up without a hitch and continues until I cut it off. (From full charge, the 100 amp hour system can provide power for about an hour or two before we get into the 10% discharge level, or 12.5 volts). In both these cases the batteries are in good shape, are both about the same age, and in both cases the batteries are fully charged when I try to use them with the TV. My hypothesis is that -- firstly -- this has nothing to do with the inverters, which are both made by the same company, Vantec, even though they are different in capacity. It is the 750 watt Vantec that works with the TV-situation anyway, not the 1500 watt one. My second guess is that the MK 100 amp hour gel battery is simply designed differently -- i.e. that although it is a "deep cycle" battery like the Universal 200 amp hour battery, it is designed more like a cross between a car battery and a normal deep cycle battery, and thus is better able to "shoot a lot of electrical juice out" when a strong surge is presented to it. BUT this is only a guess, however. I should add that when the device that I run in question has a lower surge draw in the beginning, that the two systems perform as one would expect them to. For example, when I run a 60 watt fan on my waterstove, the 200 amp hour Universal goes significantly longer than the MK 100 amp-hour battery before it drops to 12.5 volts (from full charge). In other words, there is nothing "wrong" with the bigger battery (or inverter) setup. If it was older, or simply in worse shape, I wouldn't be scratching my head. So my question is: What is the reason for the smaller battery being able to handle the greater surge? Am I right in guessing that the MK gel battery is simply different in design? Or are gel batteries themselves known to be able to handle surge better than AGM batteries (I've never read or heard this before)? I really am curious if anyone knows the answer, and would really appreciate any comments anyone might have.
editor says;
Try putting some whitespace in your post. One long unbroken lump really SUX to read

Trying to Figure something out! | 13 comments (13 topical)

Uh first thought. (3.00 / 0) (#1)
by TomW on Sat May 20, 2006 at 06:29:13 AM MST

radiantboy;

First thing to check is battery to inverter wiring [size and connections]. A crappy connection or small wire there can cause a lot of that type problem with a resistive connection or small cable dropping a lot of voltage.

Just the first idea.

All inverters, even within one model line, are not created equal, either.

Cheers.

TomW

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

To all of you, thanks--it worked! (3.00 / 0) (#12)
by radiantboy on Sun May 21, 2006 at 03:38:18 PM MST

Well, I checked the size (and yes, length --good point, snorth!) of the wires between the battery and the inverter (by the way, I even got the brand name wrong -- it is a Vector inverter, not a Vantech -- Idon't know where I got that, and I've had this setup for two + years!). The wires were not even #10, I don't think, but were probably #14 or even smaller I estimate. Furthermore, the length was about 1 foot. (On the Exceltech I have much bigger cables, but perhaps they are too long. I shall see . . .)

So, this afternoon, I put what is probably at least #8 cable between the Vector inverter and the battery. In addition, some of you guessed right -- I was using alligator clips on the batter terminal side of the connection. I replaced these with proper nut and bolt connectors. And lastly, the length of the cables I shortened to about six inches. Now the inverter has to sit on top of the battery because the cables are so short!

Well, then I turned the inverter on and came inside. (This is a 12 volt system, so when I assembled it, I had a carpenter build a small structure to house the batteries, inverters, and charge controllers so that they would be nearer the solar panels, which are about 60-70 feet from my house -- thus less voltage drop). I turned on the strip with my monitor and lo! it came on instantly!!! There was absolutely no "burping" (as oztules aptly described this phenommenon of cutting on and off.).

So then -- the big test! Would it run the Sony 27" television as well??? With great expectations, but not really completely sanguine about it working on the TV as well, I plugged it in and turned the TV on immediately. It came on without one single burp! I still feel fantastique, incredible!!

I really want to thank all for their posts. Although I haven't responded to each one individually, and have left a lot out, you pretty much all pinpointed the problem exactly. I really appreciate it. You know, I've been putting up with this "burping" for around 2 years and didn't know the cause. When we've had fairly long power outages here in Alabama, in the past couple of years, I wasn't able to use this setup to power my Sunfrost fridge (the most important thing during an outage, I believe). Well, maybe I can now . . . !!! In any case, at least I can run the televsion now, whereas before I could not.

Again, thanx a million!!

[ Parent ]

Re: To all of you, thanks--it worked! (3.00 / 0) (#13)
by srnoth on Mon May 22, 2006 at 07:20:03 PM MST

Hey radiantboy,

Great! Glad to here you got it worked out. You should definitely be able to power your fridge now :-). I can power mine of a 800w inverter with no problems now that I replaced my cables. It seems strange that the manufacturers never bothered to mention this, especially as it can make their products look bad. Hmm.

By the way, I wouldn't put the inverter directly on the battery if I was you. I'm not 100% positive that it will be damaged, but I've seen what battery acid can do to concrete, and I wouldn't put anything valuable where it could come into contact with the acid. For my system, I used an old floor standing bookshelf, put the batteries on the lowest (floor) shelf, and put my inverters on the shelf above that, so that they are very close to the batteries, ontop them basically, but still not in contact with them. I would definitely find some way to keep the inverter from actually touching the batteries.

Hope all works out for you,
Cheers,
Stephen.

P.S. 'srnoth' not 'snorth', lol. Stephen Roger Nothnagel. I need to come up with a better username, hehe.

[ Parent ]

Re: Trying to Figure something out! (3.00 / 0) (#2)
by fungus on Sat May 20, 2006 at 06:32:48 AM MST

You could maybe try putting a large capacitor in parallel with the battery to soak up the surge load, like the ones used for massive car stereos.

'Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.'-Albert Einstein
Fungus - www.reenergy.co.uk

Re: Trying to Figure something out! (3.00 / 0) (#3)
by wpowokal on Sat May 20, 2006 at 06:33:59 AM MST

Bloudy hard to read without paragraphs, but one suspects the surge is caused by the degausing circuit on the monitors.

allan
"Dream as if you'll live forever, live as if you'll die today." James Dean

Re: Trying to Figure something out! (3.00 / 0) (#4)
by oztules on Sat May 20, 2006 at 06:58:04 AM MST

First thig to do is what Tomw suggests... check for a highr resistance path in your lnput lines (dirty/poor connection)..... I doubt this but it's worth a check

Second. If you suspect the battery matrix then change the batteries over and retest.

My gut feeling is that it is probably not the battery, but your batt to inverter wiring, fuse/wiring........or more likely

.. the current regulation in the bigger inverter is much faster to cut in, and the time delay before recovery is too long (burping circuit timing). The time between cut of from surge to restart is longer then the discharge of the inrush caps in the telly, and so it can never catch up with the current.

In the monitors case, quick successions of almost starting allows the capacitors in the pwm to incrementally increase until on the fith or so start, the inrush current is less than the inverter trigger set.

This is all conjecture.... just swap the batteries and see if it is batts or inverter.

................oztules

Re: Trying to Figure something out! (3.00 / 0) (#5)
by Gary D on Sat May 20, 2006 at 06:59:04 AM MST

I agree with Tom's thought, and the second thought along those lines is- don't use the alligator clips. If you clip em off and hard wire to the battery, you will have a better connection. Just a thought.

Re: Trying to Figure something out! (3.00 / 0) (#6)
by drdongle on Sat May 20, 2006 at 08:02:22 AM MST

I have to ageree, check for corroded or loose connections. Also wire size may be to small.
Carpe Vigor, Dr.D
[ Parent ]

Re: Trying to Figure something out! (3.00 / 0) (#7)
by henjulfox on Sat May 20, 2006 at 08:15:24 AM MST

I agree with the consensus - Battery cable too small and/or bad connections. What size cable/connection method are you using?
-Henry

Re: Trying to Figure something out! (3.00 / 0) (#8)
by Nando on Sat May 20, 2006 at 08:54:20 AM MST

HECK trying to read your "monologue" message does give a head ache, is like listening to a Fast Monologue.

Even both converters may have been manufactured by the same company, you have not indicated if you have switched converters or batteries positions to see if the culprit is the converter.

Of course loose or corroded connections could be a culprit as well.

Nando

Re: Trying to Figure something out! (3.00 / 0) (#9)
by Flux on Sat May 20, 2006 at 09:23:00 AM MST

I tend to think that the surest way to prove things is to swop the inverters.

The others are right about lead resistance and connections, but the big inverter may be harder pushed than the small one and its continuous rating may be higher but the short time rating may be no more than the small one and it may be able to sustain it for a shorter time.

If you measure volts directly on the inverter terminals you can check that the volts are not dropping below inverter cut out volts. Even that may be different for the two inverters.
Flux

[ Parent ]

Re: Trying to Figure something out! (3.00 / 0) (#10)
by radiantboy on Sat May 20, 2006 at 04:34:53 PM MST

First, thanks to all of ya'll for your comments! I feel a bit overwhelmed by the sheer number of responses. I didn't even check back until now (late afternoon), thinking that probably no one would have posted any response yet. I was quite wrong!:-)

Second -- sorry for the "one paragraph" format. I forgot to put breaks using html code there. I really meant to do this, for I hate it just as much when it is just one long monologue, as if I'm into some stream-of-consciousness nonsense.

I have thought about changing the batteries and inverters to see what would happen. I haven't done this, though. I should have done so before posting. Duh!

I didn't mention this in the first post since it complicates things a little, but I do have another 200 amp hour battery and an Exceltech 1100 watt sine wave inverter connected together (which is totally separate from the Vantech 1500 watt/200 amp hour battery). And yes, I get the same problem with that system that I do with the Vantech. (You may wonder why I have two big 200 amp hour batteries and two inverters and two charge controllers instead of joining the two 200 amp hour batteries in parallel and using just one charge controller and inverter. Well, long story, so I won't tell you. But my next system will be more logical -- i.e. there will be several big batteries with one controller and one inverter . . . )

I will check the wiring (or the connections) between the battery and inverter. I think I used #10 in both cases, however. Since most of you mentioned this, I figure that will be the first avenue of investigation. While I was initally skeptical that that might be the culprit, it could very well be after all! Never discount anything, especially if you're not an expert, like myself!

wpowokal states that the surge may be caused by the "degausing circuit on the monitors." I assume this is normal, right? I mean, there is no way of avoiding this is there? The degausing is just the usual operating procedure of the monitors, isn't it?

fungus states "You could maybe try putting a large capacitor in parallel with the battery to soak up the surge load, like the ones used for massive car stereos."

Is this easy? I'll have to investigate this possibility too, as it sounds fairly commonplace, since it is used in massive car stereos . . .I did have the thought that a capacitor would be nice -- but I have no idea of how to install one, or what size or type to get etc. etc.

In conclusion, I have learned something. Before, I was almost certain that there was a fundamental difference in battery design, even between two "deep cycle" type batteries involved, the MK and the Universal. But now I see that I am certainly in the minority on this score -- and I suspect -- deservedly so, since nobody here even gives my conjecture the least credibility, even to mention it. Ha ha! I am more of technical newbie that I realized! It is good to be humbled. My lack of wisdom must be salient indeed. But that why one asks questions, to learn.

Anyway, thanks again to all!!

Re: Trying to Figure something out! (3.00 / 0) (#11)
by srnoth on Sat May 20, 2006 at 09:36:22 PM MST

Hey radiantboy,

#10 cable???? No wonder. How long is it?

I think it is most definately the connection between the inverter and the batteries that is causing the problem. First of all, don't use the wires that come with the inverter, since these cannot handle the full current capabilities of the inverter.

Now, about replacement cables. I have an 800W (2000w surge) AIMS inverter, and I have it connected to 2 computers, a TV and some florecent lights. None of these loads come up to 800w total, more like 600w. Anyway, if one of the monitors is off for a while, and I turn it back on, all the lights dim, and the computers sometimes reboot. When I checked the voltage lost between the inverter and the battery, at around 600w, it was about .6 volts! And that is only for 600w. So when it surges to almost 1200w when the monitor first turned on, it must have been about 1.2v lost! That means that if the battery was at 12v, the inverter was only getting 10.8! Anyway, this was obviously the cause, so I replaced the original cables with some #8 car amplifier cable from radioshack, and I only used about 1 foot of cable between the batteries and the inverter, so now my voltage loss is down to about 0.1v. If have seen a definate improvement. The lights still dim a bit, but the computer's don't reboot.

So, I would shorten the cable distance between the batteries and the inverters, and also use thicker cable (at least #8).

Oh, and about the smaller inverter working but the more powerful one not, I think this may be the reason. When these newer inverters are connected to a device with an initial surge that is greater thatn the inverter can handle, most modern inverters drop their output voltage so that the surge can build up gradually. This is sometimes called 'soft start' or something like that. Anyway, this limits the initial surge current to something the inverter can handle. On the smaller inverter, the maximum surge current would be less than that of the big inverter, so the voltage drop in the cables may not be high enough to cause the inverter to turn off. However, the bigger inverter can supply a much higher initial surge current, so it allows this much higher current to flow to your tv. However, you said that they both use #10 wiring, so that means the voltage drop between the batteries and the inverter will be higher, meaning that the inverter will be getting less than the 10.5v it needs to operate, so it shuts down. That seems to me to be the most likely reason why the smaller inverter works and the bigger one doesn't.

Hope this helps,
Cheers,
Stephen.

[ Parent ]

Trying to Figure something out! | 13 comments (13 topical)

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