High amperage draw on inverter/batteries

[ERTF]

I now have 1700w of solar. Every sunny day, a large portion of that is going unused. I have a 1000w water heater. Needs about 45-60min for a winter shower. Thinking I might as well use some of that excess solar power to make hot water. Two questions:

1. My inverter is an old Xantrex Freedom 10 1000w. I have run tools/appliances that are slightly over 1000w and never popped the breaker, so theoretically it should work. My question is if 1hr daily of near max capacity will eventually kill the inverter?
2. I have about 1100ah of new lead acid. If i'm pulling 85-100amps out of the bank for an hr daily, will that prematurely degrade them? Also would it make a difference if I run the water heater during the afternoon when the panels are pumping in a large portion (or possibly all) of that load?

 

[O C Diver]

Confirm the water heater element, most are 1,200 to 1,500 watts.

I would want to do this when the solar is offsetting some of the draw. Probably want to check with the battery manufacturer to determine the maximum continuous draw.

I don't think it's a good long term idea to max out the inverter.

However, I believe you could swap the element which is 120 VAC for the same wattage 220 VAC. In essence, at the lower voltage you would about half the wattage and amperage. It would take twice as long to heat the water, but your inverter would be happier.

Please verify the above before attempting to do it.

Ted

 

[mvweebles]

Missing some information. This is a mass balance equation.

1700w of solar is big. 8-9 square meters which is big. A 1000w inverter is really small. Very small. 1100 ah of battery capacity is big. Really big. Something is wrong here.

Need to understand your system, your boat, and your use-case. Depending on your location, 1700 w of solar should deliver at least 8kwh of power in the summer (less on annual average). That's more than enough to power an off-grid cabin. 1000w inverter is your choke point. Frankly, I'm stunned you have so much solar and such a small inverter. Either I made a mistake or something else is amiss.

Peter

 

[DavidM]

You can install a 220v heating element in your water heater and run it on 110v from your inverter. That will cut the wattage in a fourth but will take four times longer to heat up.

My buddy did this for exactly the reason you describe.

David

 

[mvweebles]

You can install a 220v heating element in your water heater and run it on 110v from your inverter. That will cut the wattage in a fourth but will take four times longer to heat up.

My buddy did this for exactly the reason you describe.

David

My understanding is wattage (power) stays the same. When voltage doubles, amperage halves. Wattage remains the same. Benefit comes if you can increase wattage. If you have small wire, might help you increase voltage and reduce amperage across same gauge wire. But in the end, 1000w heating element is roughly the same whether 240v x 4 amps or 120v x 8 amps.

If OP has1700w of solar and 1100ah of battery capacity, OP needs to rethink the 1000 watt inverter. And charger.

Peter

 

[rslifkin]

My understanding is wattage (power) stays the same. When voltage doubles, amperage halves. Wattage remains the same. Benefit comes if you can increase wattage. If you have small wire, might help you increase voltage and reduce amperage across same gauge wire. But in the end, 1000w heating element is roughly the same whether 240v x 4 amps or 120v x 8 amps.

For a load that pulls constant power, you're correct. But a heating element isn't constant power. It's a straight resistive load. So if you have a heating element rated for 1200 watts at 240 volts, it will have a resistance of 48 ohms, which allows 5 amps to flow at 240 volts. Cut the voltage in half with the same resistance and the amperage will also be cut in half (48 ohm element at 120 volts passes 2.5 amps, so 300 watts). So 1/2 the voltage = 1/4 the power for a resistive heating element.

 

[DavidM]

For a load that pulls constant power, you're correct. But a heating element isn't constant power. It's a straight resistive load. So if you have a heating element rated for 1200 watts at 240 volts, it will have a resistance of 48 ohms, which allows 5 amps to flow at 240 volts. Cut the voltage in half with the same resistance and the amperage will also be cut in half (48 ohm element at 120 volts passes 2.5 amps, so 300 watts). So 1/2 the voltage = 1/4 the power for a resistive heating element.

Correct.

David

 

[mvweebles]

For a load that pulls constant power, you're correct. But a heating element isn't constant power. It's a straight resistive load. So if you have a heating element rated for 1200 watts at 240 volts, it will have a resistance of 48 ohms, which allows 5 amps to flow at 240 volts. Cut the voltage in half with the same resistance and the amperage will also be cut in half (48 ohm element at 120 volts passes 2.5 amps, so 300 watts). So 1/2 the voltage = 1/4 the power for a resistive heating element.

Got it. Thanks. However it does not answer the OPs questions. He asked of its okay to max-out the inverter capacity for an hour, and whether it would damage his battery bank. Specifically said he wasn't popping breakers (which amazes me given a 1000w inverter). He doesn't need to feather power. In fact, issue is rhe opposite. He has so much power he is trying to figure out how to use it

No idea if his old Xantrex can handle a steady load at max 1000w. Better quality inverters are rated to deliver stated capacity for 24 continuous hours. An older Xantrex might do fine if well ventilated and not in a hot environment.

If you run your 1000w water heater during the day, your 1700w of solar will easily replenish the demand. Should have virtually no effect on your 1100 ah battery bank.

What I don't understand is why someone would go through the expense and effort to put a 1700w solar array and a 1100 ah battery bank on a boat and only have a 1000w inverter. Just seems like an odd design, especially since decent inverters are so cheap these days. I just put a 2000w PSW inverter in my van and it was $350 for a decent quality one.

Peter

 

[O C Diver]

For a load that pulls constant power, you're correct. But a heating element isn't constant power. It's a straight resistive load. So if you have a heating element rated for 1200 watts at 240 volts, it will have a resistance of 48 ohms, which allows 5 amps to flow at 240 volts. Cut the voltage in half with the same resistance and the amperage will also be cut in half (48 ohm element at 120 volts passes 2.5 amps, so 300 watts). So 1/2 the voltage = 1/4 the power for a resistive heating element.

Thank you for correcting me on the power reduction factor.

So it appears that the simple solution would be to replace the 1,000 watt 120 VAC element with a 2,000 to 2,400 watt 220 VAC element which would yield 500 to 600 watts of heating.

Ted

 

[FF]

Many larger sized HW heaters have 2 heating elements.

The Alt energy folks have both 12v and 24v heating elements that would fit in one.

Not as efficient , but some folks have simply hooked the solar DC up to a std. AC element if the DC is available for long periods.

 

[Iggy]

My understanding is wattage (power) stays the same. When voltage doubles, amperage halves. Wattage remains the same. Benefit comes if you can increase wattage. If you have small wire, might help you increase voltage and reduce amperage across same gauge wire. But in the end, 1000w heating element is roughly the same whether 240v x 4 amps or 120v x 8 amps.

If OP has1700w of solar and 1100ah of battery capacity, OP needs to rethink the 1000 watt inverter. And charger.

Peter

Yep! I would install, but thats me. A charger/inverter in the 3000 watt range.

Now Isotherm makes water heater that uses 750 watts at 120v. I had a 5gal one in my old boat and it took 20 minutes at 70 degrees to heat up. I was very happy with it!

 

[ERTF]

Missing some information. This is a mass balance equation.

1700w of solar is big. 8-9 square meters which is big. A 1000w inverter is really small. Very small. 1100 ah of battery capacity is big. Really big. Something is wrong here.

Need to understand your system, your boat, and your use-case. Depending on your location, 1700 w of solar should deliver at least 8kwh of power in the summer (less on annual average). That's more than enough to power an off-grid cabin. 1000w inverter is your choke point. Frankly, I'm stunned you have so much solar and such a small inverter. Either I made a mistake or something else is amiss.

Peter

What's so hard to understand? The inverter came with the boat, and until I recently added a 120v chest freezer, basically nothing ran on it for more than a couple minutes like a microwave or toaster (my fridge is 12v).

 

[ERTF]

Confirm the water heater element, most are 1,200 to 1,500 watts.

I would want to do this when the solar is offsetting some of the draw. Probably want to check with the battery manufacturer to determine the maximum continuous draw.

I don't think it's a good long term idea to max out the inverter.

However, I believe you could swap the element which is 120 VAC for the same wattage 220 VAC. In essence, at the lower voltage you would about half the wattage and amperage. It would take twice as long to heat the water, but your inverter would be happier.

Please verify the above before attempting to do it.

Ted

I know for a fact it's 1000w

 

[ERTF]

Yep! I would install, but thats me. A charger/inverter in the 3000 watt range.

Because for example a victron 3000w inverter charger costs $1300. Considering i take cold showers from about memorial day to halloween. And then dont take a shower EVERY day of the remaining 7months, so (at 45-60min) we're talking 125-150 hrs of gen a year. Which means the potential financial payoff might take a decade. So it's not exactly a no brainer situation where I feel i gotta run out and drop that kind of cash before thinking it through thoroughly because I already have a working inverter/charger and 2 generators that otherwise barely get used. I just added 1200w of panels this summer and I don't even start taking hot showers until late october, so this thought process is in it's infancy. It might make more sense just to buy a cheap stand alone 2000w inverter just for the water heater.

 

[ERTF]

Missing some information. This is a mass balance equation.

1700w of solar is big. 8-9 square meters which is big. A 1000w inverter is really small. Very small. 1100 ah of battery capacity is big. Really big. Something is wrong here.

Need to understand your system, your boat, and your use-case. Depending on your location, 1700 w of solar should deliver at least 8kwh of power in the summer (less on annual average). That's more than enough to power an off-grid cabin. 1000w inverter is your choke point. Frankly, I'm stunned you have so much solar and such a small inverter. Either I made a mistake or something else is amiss.

Peter

I frequently see these theoretical solar proclamations, and they always fail to recognize that the purpose of a large array is that it still puts in a significant charge on cloudy days. And additionally after a stretch of dark rainy days, one sunny day can get you back to top. Solar panel are so cheap and maintenance free that if you have the hardtop space it's a no brainer. If you have more power than you can store, leave the inverter on 24/7, install cheap AC appliances, less need to monitor charge closely. There's plenty of benefits.

 

[mvweebles]

What's so hard to understand? The inverter came with the boat, and until I recently added a 120v chest freezer, basically nothing ran on it for more than a couple minutes like a microwave or toaster (my fridge is 12v).

Surprised your microwave will run off a 1000w inverter. Even though inverters have 2x surge capabilities, a small microwave usually trips the over-current protection.

It's just odd to see a system with so much solar, so much battery capacity but such a small inverter. Maybe the previous owner swapped out prior to sale. Who knows. Big solar snd battery on a boat these days often means owner wants to run AC from batteries.

Suggestions to reduce wattage on water heater are good. Running at full inverter capacity may have no I'll effect, but it might. An alternative would be to pickup am inexpensive standalone 2000w inverter to power just the water heater. Install a selector switch inline to chose either power from panel (presumably fed by the 1000w inverter), or the 2000w secondary inverter.

Good luck.

Peter

 

[mvweebles]

I frequently see these theoretical solar proclamations, and they always fail to recognize that the purpose of a large array is that it still puts in a significant charge on cloudy days. And additionally after a stretch of dark rainy days, one sunny day can get you back to top. Solar panel are so cheap and maintenance free that if you have the hardtop space it's a no brainer. If you have more power than you can store, leave the inverter on 24/7, install cheap AC appliances, less need to monitor charge closely. There's plenty of benefits.

Not theoretical. I have designed and installed four solar installations from small (camper van) to a grid-tie system for a condo in Yucatan that is net-zero. Other two are a friend's off-grid cabin in Wyoming, and of course my boat with an 800w array and 700ah of lithium. I definitely understand benefits of oversize arrays snd battery capacities. But without a large inverter, it's just tough to consume more than 250 ah per day.

Getting the sense either your question is answered, or it wasn't really a question.

Peter

 

[O C Diver]

I know for a fact it's 1000w

For someone who comes looking for help / opinions, you bring an awful lot of attitude with you. A viable option was offered and you seem ungrateful. You make it hard for people who are trying to offer you options.

Ted

 

[ERTF]

The problem with the smaller element solution is if you wake up in the morning and gotta go somewhere, you don't wanna wait 2-3 hours for a hot shower.

 

[JDCAVE]

As others have mentioned, I think the OP needs to seriously consider a bigger/newer inverter. 1000 amps is too small IMO. Juggling loads will only go so far.

Jim

 

[O C Diver]

The problem with the smaller element solution is if you wake up in the morning and gotta go somewhere, you don't wanna wait 2-3 hours for a hot shower.

Ok, if a 1,000 watt 120 VAC element heats your water in an hour. A 3,000 watt 220 volt element in this situation will do it in 1 hour and 20 minutes and will reduce the load on your inverter to 750 watts.

If you search water heater elements, you will find many more wattage options than 120 VAC. There are also ones that are folded over for short diameter tanks

Ted

 

[mvweebles]

For someone who comes looking for help / opinions, you bring an awful lot of attitude with you. A viable option was offered and you seem ungrateful. You make it hard for people who are trying to offer you options.

Ted

What the OP wants to hear is that his inverter is rated for 1000W continous output, which it is. What he doesn't want to hear is skepticism that running something at 100% usually doesn't work well, especially as things age.

In this case, I'm good saying with 100% certainty that my recommendation is the OP go for it. No need to de-rate the water heater.

Good luck -

Peter

PS - thanks to several on the Ohm's Law lesson. I had never thought of this in relation to pure resistnce. I definitely learned something today -

 

[ERTF]

It's just odd to see a system with so much solar, so much battery capacity but such a small inverter. Maybe the previous owner swapped out prior to sale. Who knows. Big solar snd battery on a boat these days often means owner wants to run AC from batteries.
Peter

Boat came to me 3 years ago with 500w solar. Wasnt enough. And i wanted a chest freezer. Had room on top of flybridge for 1200w more. Could have dinked around adding panels til I got just the right amount (until it was cloudy for a day), but I just went big and put as many up there as I could fit.

I knew I could add draws like water heater. Potential A/C off batteries was also a consideration, but even with all that solar, I'm not sure it adds up to much A/C. If I'm gonna try A/C I will need the big inverter, so that may end up being the option in the end.

As it is, I draw a lot of power overnight in the summer: 10 amps of 12v fans for me/gf, plus fridge, chest freezer, inverter. That's a couple hundred amps while it's dark, which means 550ah usable isn't so excessive. And the solar pumps them right back up even if it's hazy. 99 problems, but battery charge ain't one. The only possibly more useful addition I have added to my boat, is my water catchment, which yields over 100 gal per inch of rain. Sure is nice to have all that hardtop...

 

[mvweebles]

Boat came to me 3 years ago with 500w solar. Wasnt enough. And i wanted a chest freezer. Had room on top of flybridge for 1200w more. Could have dinked around adding panels til I got just the right amount (until it was cloudy for a day), but I just went big and put as many up there as I could fit.



I knew I could add draws like water heater. Potential A/C off batteries was also a consideration, but even with all that solar, I'm not sure it adds up to much A/C. If I'm gonna try A/C I will need the big inverter, so that may end up being the option in the end.



As it is, I draw a lot of power overnight in the summer: 10 amps of 12v fans for me/gf, plus fridge, chest freezer, inverter. That's a couple hundred amps while it's dark, which means 550ah usable isn't so excessive. And the solar pumps them right back up even if it's hazy. 99 problems, but battery charge ain't one. The only possibly more useful addition I have added to my boat, is my water catchment, which yields over 100 gal per inch of rain. Sure is nice to have all that hardtop...

Pictures? What kind of boat are we talking?

 

[ERTF]

What the OP wants to hear is that his inverter is rated for 1000W continous output, which it is. What he doesn't want to hear is skepticism that running something at 100% usually doesn't work well, especially as things age.

In -

If that was the case I wouldn't have asked the question. I never said anybody was wrong about that. In fact there was very little discussion in this entire thread about my actual question.

All I said anybody was wrong about was the wattage of things I installed on MY own boat.

All these suggestions such as larger inverter, stand alone inverter, smaller element had already been considered by me. I first simply wanted to ask if my current setup would be hard on the inverter/batteries. It was a valid question and somebody even responded that modern units are rated for max wattage for 24hr continuous. Geeeez

 

[ERTF]

Pictures? What kind of boat are we talking?

Marine Trader 44 CPMY

 

[mvweebles]

TF is a pretty conservative bunch when it comes to spec'ing equipment. You'd be hard-pressed to get a recommendation to run full-throttle on anything no matter what the OEM says. But you may want to ping Xantrex, or maybe talk to one of the niche suppliers such as DonRowe.com or InvertersRUs.com. They are likely to have precise explanations if it is indeed a bad idea. If you do reach-out, please update here - I've already learned a couple things in this thread. Always open for more.

Maybe de-rate the heating element and put the water heater on a timer so you have a nice shower in the morning.

https://www.amazon.com/dp/B00MVEMD76/ref=cm_sw_em_r_mt_dp_TBNVRYNGHJSJ51XAM73F

Frankly, fact that you can run microwave on your 1000W inverter is a good sign that your inverter runs fine. Even a small 700W one pulls well over 1000W. I have seen 1500w inverters be unable to shoulder the load of a small microwave.

BTW - I was the one who said that inverters are rated for 24hr continuous load. I just don't believe it. But I also said needs proper ventilation and cool/dry storage.

Peter

 

[ERTF]

Panels

 

[ERTF]

My microwave is 950w. Blender is 1000w. I also accidently ran (turned on gen but forgot to flip switch) a 1560w pressure washer thru inverter (off and on) for an hour, and somehow didn't pop anything. In the end I may end up getting a bigger inverter, but for me personally I just don't need to run my toaster and a power tool at the same time, so it's never been an issue. If the inverter chargers weren't so spendy it'd already be a done deal.

 

[CharlieJ]

@ERTF:

I have about 1100ah of new lead acid. If i'm pulling 85-100amps out of the bank for an hr daily, will that prematurely degrade them?

You are not doing your batteries any favors by hammering them so hard. Assuming that the 1100Ahr of capacity is the conventional 20 hour rate than any load > 1100Ahr/20hr = 55A is taking service life from your batteries. This is not opinion, it is a fact that can be verified by looking at the battery manufacturer's service life curves.