Capacity Testing and 20 HR Rating

No 600w microwaves in Canada, it seems... only u.s., and overseas.

I'm wondering if beefing up the wiring from bank to inverter would help alleviate some of the stress on the inverter while powering the MW? I have about 2' of pos and about 4' of neg, 2ga. And a 100a catastrophe CB; which I'm surprised has never tripped.

Salvo wrote:
Neglecting to account for the microwave's PF is reason for the demise of the inverter.

jrnymn7 wrote:

BFL mentioned toasting an inverter, but I'm not sure if it was the xantrex 1000??? This may be a sign to stop pushing the unit so hard with the MW; even though it is supposed to handle much higher peak loads for up to 5 minutes.

Salvo,

How would one go about that? And is it a combination of poor efficiency and line loss, or is one simply the result of the other?

My Can Tire (Xantrex built) 1000w PSW inverter (Spec says 1000w continuous rating NOT 900w) ran the 700w Danby microwave ( wants 1050w input) just fine several times and then it went poof. Took the lid off and there was a nasty looking black splotch around one area of the circuit board. Beyond my DIY skills :(

When it was doing ok running the microwave, it was showing 1050 on its watt meter display and the yellow overload lamp was on. (being over 1000w at the time) It was drawing around 100a according to the Trimetric, which is correct according to the "divide by 10" rule.

That's all I know about that. Somebody else's same model inverter might do better or worse, no idea.

Neglecting to account for the microwave's PF is reason for the demise of the inverter.

jrnymn7 wrote:

BFL mentioned toasting an inverter, but I'm not sure if it was the xantrex 1000??? This may be a sign to stop pushing the unit so hard with the MW; even though it is supposed to handle much higher peak loads for up to 5 minutes.

Journeyman the 15% was a deliberate exaggeration to skew perspective against what I practice. I may actually give up 2-3% life with those monster .330" plates.

There is even more factors to consider. One of the more important is antimony poisoning o the lead oxide negative plates. The less time spent in the 14.4 - 14.8 volt area, the less antimony will migrate. The 14.4 really is not a floor. It is a linear decrease to insignificant levels around 13.6 volts. This is why I cringe when I read threads where folks spend hours and hours at high voltages trying to attain full specific gravity.

But other issues cloud the picture. So called cyclable flooded batteries with less than 5% antimony are an oxymoron. With peer pressure BCI is trying to leverage battery alloy standardization. Sort of like recyclable beverage containers whose materials tolerance bandwidth is very narrow. A specific PPM deviation limit is holy writ.

Batteries are snotty. Fail to give them what they want and they end up pounding nails into the coffee table. But the rhetoric from some of the OEM's borders on asinine. A 2.75% antimony flooded battery from one manufacturer must have extremely similar characteristics (similar BCI group and cell plate count) from another manufacturer. If for some reason they are dissimilar then one is inferior. Period.

I may wish to add, much of the comments above apply to generator recharging. With unsubstantial solar voltaic capacity, a lot of time may be spent at 14.4 to 14.8 volts trying to achieve full charge. I manage solar voltaic charging by running the generator for 20% of the bottom ampere hours and for the last 10%, if the last 10% takes longer than 2-hours to 100% SOC with panels only. Percentages are hydrometer readings.

Hi jrnymn,

Yes BFL's inverter was a rebranded Xantrex 1000 Psw which died from running a microwave.

I have yet to see any evidence that high current "speed" charging causes decreased life expectancy. It seems, as long as voltages do not far exceed gassing voltages, the battery will not be harmed. But as you say, even a 15% drop in cycle life would be a worthwhile trade off. Up here, gas is about $5.20u.s. per u.s. gallon. A 4 hour (top end) charge, (just to replace a measly 50-60Ah's), using the Honda 2000 and a 45a charger, costs about $2.60u.s.. It doesn't sound like much, but those tables in the article really put things into perspective, efficiency wise.

on a different note;

I used the microwave this morning, and I paid close attention to what the various meters had to say regarding wattage, amp draw, and Vbatt. Until recently, I thought the xantrex prowatt 1000 inverter's wattage reading was way off, but now I realize it was due to significant line loss. The amp draw seemed way too high for a 1080w draw, but I recently realized I was ignoring voltage drop. It turns out, Voltage out of the inverter was dropping to less than 100v. 1080w / 11a = ~98v.

But what really caught my attention was the discrepancy in Vbatt readings, while the MW was running. Bank was at ~93%, -29Ah's, 12.77ocv. According to the multimeter, Vbatt dropped to 11.81v, but according to the inverter, Vbatt dropped to less than 11v and shut down, about 2 minutes in... much to my surprise. After about a 5 minute rest, during which time the inverter's fan ran full out for the most part, I ran the MW for an additional minute (bound and determined to have scrambled eggs), with no (~11.5v)alarm or (~11v)shutdown. Turned off inverter, and 20 minutes later, Vbatt rebounded to 12.76ocv. So bank had no problem handling the load, it seems.

BFL mentioned toasting an inverter, but I'm not sure if it was the xantrex 1000??? This may be a sign to stop pushing the unit so hard with the MW; even though it is supposed to handle much higher peak loads for up to 5 minutes. I'd love one of those inverter MW's but they're physically too big, even the 800w models. A 600w MW might work, if such a critter exists? But for now I'm gonna try using 'power 80', and see how that goes.

When time is money with a running generator crunching numbers soon brings up the combined cost/time factor of using a genset. Pistons, recon rods, liners and a new overhead will set me back around 4K. Throw in a camshaft, followers, injector pump, gaskets and bearings plus turning the crankshaft and it adds up to real money. The Kubota running at 70% load does not eat that much more fuel than it does at 40%. Fuel is $3.55/gal US But it's the seventy-mile round trip that's a killer just for fuel.

So I whack perhaps 15% off the cycle life total by full absorbsion limit charging but reduce charhing time by 35%. I have must have spent 100-hours crunching numbers and no way can "ideal" charge levels compete. In my scenario it would be a joke.

Factoring generator size, manageabiliy, cost, then paying for large chargers enters the picture. I have fun crunching numbers - others get migranes.

Then there is intangibles - do I want to listen to a generator rattling all day?

But utilizing 10% of a 3 000 watt generator to pray to the "ideal" C gods is silly and expensive. Battery companies wish to make their product look as good as possible. Hang the expenses.

Mex,

Regarding the 'ev battery monitoring' link;

I've read a similar article in the past, and I remember discussing this idea of what they call the "amp hour law" in another thread. And if I'm not mistaken, this is essentially what you have been recommending, when you talk about achieving instant absorption voltage. This means, a 430Ah bank, at 50%, could accept 215 charging amps without any issues. Boy, that sure flies in the face of the usual C/10 rates we often read about. And the guys at powerstream dot com would agree.

But putting using a 215a charger aside, as I perused the article, it dawned on me that the ideal Vabs setting would be one that brings the bank to an SOC at which amps would begin to taper just as the amount of Ah's missing is equal to the chargers current limit. As it is, at a little under 14.8v, my pm4b-45 begins to taper amps at about 91%... which happens to be about 39Ah's missing. At 14.8v (t.c.), my bank gasses a little more than I would like to see, (or hear, or smell), so it seems if I was to lower the Vabs somewhat, it would cause amps to taper a little sooner, like around 89% (45Ah's missing), and it would reduce gassing somewhat.

In one sense, this is nothing new, but it may be a practical answer to the common question of what constitutes an appropriate charging voltage. So, if you're using a 30a charger, find a Vabs setting that causes amps to taper at about 30Ah's from full. With a 75a charger... about 75Ah's from full. So, using my pm3-75 on my 430Ah bank, the proper Vabs setpoint would cause tapering to begin at about 82% soc (-75Ah's).

Hmmm, now that you mention it, Mex, I had my electrolyte levels just above the plates when I did the C test and associated SG readings... I hadn't topped them up for the summer yet. Perhaps I should have mentioned that? Anyhoo, my concern was more about how the individual batts, and their individual cells, performed in relation to one another. That's also the main reason I wasn't concerned with temp compensating the readings.