Small battery bank running an inverter

[a64pilot]

It's not free, especially if the load is at .5C. That will shorten the life of the batteries, and we don't know how much Solar he has, but I am real suspicious of his bank being charged before noon.
Combine heavy discharge rates with chronic undercharging, and I don't think he will get the three yrs out of this bank that he wants.

I'll agree to the free part if Diesel is being burned anyway and it can come from a generator or an alternator.

Look at it another way, he has a 200 AH bank, or 100 AH useable. (at a 20 hr discharge rate) He eats through more than 20% of available power making a pot of coffee, maybe 30%? I don't know.

[Redline452]

Our Nespresso Citiz makes a cup of coffee on about 1 AH ea; the draw while heating is an intermittent 115 Amps at 12V via a Magnum 2812 2500 watt true-sinewave inverter. It's a big draw, but at about 50% duty cycle for only a minute. Two cups of coffee plus an Aeroccino heating/frothing the milk takes a total of 3AH, which is easily replaced by our solar.

Voltage from the 3 Group 27 FLA does sag during heating cycles, but not for long. Two batteries would probably might handle it, while it's over 100A draw, from the battery's point of view, it's probably not much worse than cranking a balky engine.

Prior to the Nespresso we happily used a percolator on propane, or French press for smaller quantities.

One caveat - these Nespresso machines don't like "modified sine wave" inverters, so you nee a "true sinewave" model, at extra cost.

[txg]

a64pilot, while your math is correct, the assumption that it takes 10 minutes at 1500w to heat a cup of water is completely wrong.

according to my victron battery monitor, when we use our 1000w kettle to heat water for coffee, it takes about 7Ah from the battery for two cups, so it's 3.5Ah for one cup and not the 21Ah you calculated. Our 280Wp solar array recharges these 3.5Ah in less than 15 minutes when the sun is shining.

With the 21Ah of your calculation we can cook pasta for three persons.

Also, there is another thing to saving propane is that it's not just about cost, it's about being able to go on longer without refueling. Everyone that is out cruising knows that it can be a real pain in the ass to get your bottles refueled in another country.

By using electricity when possible we cut our usage (though it is ethanol for us, but that's not the point here) in half and so we can double the amount of time we can be out cruising before finding some place to refuel. That's a big difference!

And the other nice thing is that you always have a backup. Must be really shitty to be out in bad weather and not even be able to make a hot tea because the gas bottle went empty completely unexpected.

Redline452, your numbers are even better than ours...probably our old Victron Atlas inverter is not the most efficient one, or the difference comes from your machine not heating the water until it is boiling as our kettle does. Still, 1.5Ah or 3.5Ah are both amounts so small that it's nothing to worry about.

[DMCantor]

We have used a french press while cruising for years, and really think its the best solution. Yes, you can get away with the electricity used by a pod machine especially with a large battery bank and plenty of solar/wind. But propane is really an easier and better way to heat water. We carry two 20-pound propane tanks, and each one lasts us at least 5 months, including heating water for dishwashing most days. We have never had a problem refilling tanks in the Caribbean, though the cost varies a lot from island to island.

[a64pilot]

One cup and a pot are a whole different matter.
I haven't used a drip coffee maker in a long time and the ten minutes was just a guess, actually all those numbers were shots in the dark, meant to be representative .
But the point is don't hammer your battery bank and expect it to last very long. Cheaper in the long run to have extra propane bottles, if you have three 10 lb bottles how long will that last? It would last us for 4 or 5 months, but we don't do any baking, I assume baking would put a big drain on propane.

I think the average cruiser has essentially a negative energy budget, by that I mean very few actually fully recharge their banks. Add a monster load like a coffee maker or a hot plate to that and it takes the bank down even further.
His Solar is kicking into float by 11 AM every day, how many think his bank is recharged by 11 AM? Very little charging goes on in float. I'd bet his bank is walking down in its state of charge and becoming sulphated.

[zboss]

Originally Posted by ramblinrod

OK, so if your coffee maker draws 1200 W and your inverter is 85% efficient that would mean it is consuming around 1500 W from the batteries.

1500W at the 11.8 V sag voltage is almost 130 A. That's a lot of juice.

Solution is more battery capacity to reduce sag, coffee maker that draws less, or adjust the inverter low voltage alarm to 11.5 or less to prevent nuisance trips.

Or run the engine when making coffee.

[a64pilot]

Originally Posted by zboss

Or run the engine when making coffee.

The more and more I study this battery "thing" and by that I mean maintaining a battery bank, not just this one instance.
The more I am coming to the conclusion that running a generator or your engine if it has a good charging system early in the morning and putting lots of amps back into the bank when its charge is low enough that it will accept it, is a good thing. I'm not talking hours here either maybe a half hour or a little longer.
In this case, I think running the engine early in the morning to make your coffee would be good for two reasons, it would keep the bank from sagging so much and would puts lots of amps back into the bank to let Solar top it off for the rest of the day.

[zboss]

Originally Posted by a64pilot

The more and more I study this battery "thing" and by that I mean maintaining a battery bank, not just this one instance.
The more I am coming to the conclusion that running a generator or your engine if it has a good charging system early in the morning and putting lots of amps back into the bank when its charge is low enough that it will accept it, is a good thing. I'm not talking hours here either maybe a half hour or a little longer.
In this case, I think running the engine early in the morning to make your coffee would be good for two reasons, it would keep the bank from sagging so much and would puts lots of amps back into the bank to let Solar top it off for the rest of the day.

In any case, when you run your windlass you are using a lot of Amps and you should run your engine, so why not for any other high amp usage? Like you said, for the 15 minutes it takes to make your coffee, run the engine up to temp and charge the batts. That's about $200 a year in diesel - cheaper than going to Starbucks everyday!

Its always a good idea to make sure your engine is good to go anyhow.

[markwesti]

No timer with this set up , for me patients first thing in the morning can be somewhat difficult . So what will be your cruising batt. set up ?

[svJasmine]

find another way to make coffee. That is too much for your bank. use propane even if its just a little camp stove.

Problem solved.

[jamhass]

To get to the real nut of this thread ...

Use propane, and a filter or French press to make coffee ...

[travellerw]

Can I ask the obvious question.. Are you using 2 12V batteries... or 2 6V batteries in series?

[captstu]

While, as others have noted, the drawdown rate exceeds the recommended rate for your batteries - there may be another problem.

Since you are drawing in the range of 100 to 150 Amps, the wire size may not be sufficient for the length.

As a quick check, put a good volt meter on the battery full charged - and turn n the inverter and coffee pot. The voltage may drop surprisingly low due to voltage drop in the wire.

My previous cat used an inverter powered air conditioner to cool a fairly large space overnight - but it took four strands of "00" on the positive and another 4 strands of "00" on the negative to run the battery wire to the inverter since the beam of the boat was 25' and the batteries split between the hulls.

I'm sure yours isn't as long a run - but anything over a few feet (remember to double the length for the return) drops the voltage very quickly when you are drawing 100 amps.

Or, get a propane burner for a french press.

[txg]

Originally Posted by captstu

While, as others have noted, the drawdown rate exceeds the recommended rate for your batteries

At least a lot of people in this thread wrote that. But is this just a feeling or is there any data behind it? I've never seen a battery data sheet with cycle life as a function of discharge rate.

A lot of people here are using golf cart batteries. At which rate are they discharged when you use a golf cart for going uphill? I have no idea about that because golf carts are very uncommon in germany (unless you play golf), but my guess is that it will be in the range of C/2 or perhaps even more.

As i said, we're doing this on a daily basis for four months now, without any problems yet. While this single scenario is certainly not enough data to prove there will never ever be a problem with these high discharge rates, it at least shows that it is possible. Do any of the "this discharge rate is too high"-guys have own (and probably bad) experiences with high discharge rates? If so, please tell me about the details.

[captstu]

TXG, My comments primarily concerned the voltage drop in the cables - since this was the "issue" I had to fix when trying to start an air conditioner off my 950 Ah AGM battery bank. In the process, I also sort of determined the discharge rate my configuration would support.

For my inverter setup to work, the connector voltage on the inverter could not measure below about 12 Volts. I had no means, such as a oscilloscope, to measure instantaneous voltage but when I "saw" a voltage of about 12 volts, my a/c would not start.

In my above post, I suggested measuring the voltage at each end of the cables - to determine the voltage drop since I found the tables (see Boat US and many other sources) to be inexact. I kept adding strands of "00" until the drop was under 0.1 volts. At the same time, I connected additional batteries until the battery terminal voltage stayed above 12.1 volts when the bank was full charged.

I found the batteries consistently met this goal when the load was less than 4 times the rating in Ah of the bank.

I neglected a serious issue - actually never thought of it - my D.C. alternators would produce a nameplate rating of 520 Amps with my twin Balmar regulators -- but no heat sensor.

Eventually, this charge rate proved to be excessive and one of the batteries internally shorted causing a run away. It was only luck that enabled us to fight the fumes, dump the bad battery overboard, and potentially save the boat.

High current are dangerous.