High amperage draw on inverter/batteries

[mvweebles]

@ERTF:





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.

Charlie - is see you're ABYC. Draw of 80-100 amps off a 1100 ah battery bank does not seem excessive to me so I'm surprised by your comment. Can you provide some context on OEM specifications? Especially if there is even 15% of his solar capacity feeding the bank in early morning would be in the 25-amp range.

Peter

 

[SteveK]

@ERTF:


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.

Please expand on this.
The 20hr time frame is for max 1100Ah, yes that is 55A average per hour.

We all seem to know that only 80% of 1100 is usable and we should not discharge past 50%. In this case 1100 x .80 /2 = 440 Ah before a recharge is needed. So far I have not seen any suggestion that we must not discharge faster than the average of the 20HR.

ETA: OP asked if he will hurt his batteries in using 85-100A in one hour of 24HR. I did not see that as a problem, he still should have 340Ah left for the remaining 24HR period.

 

[ERTF]

I called Xantrex and they said it wouldn't be hard on the Freedom 10 running a 1000w water heater for 1 hr per day. When I said 1 hour, the tech replied "Just one hour??...no problem."

 

[ERTF]

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

So this element will pull 750w, take 25% longer, but use the same amount of total power to heat a shower?

 

[rslifkin]

So this element will pull 750w, take 25% longer, but use the same amount of total power to heat a shower?

With that element running at 120 volts, yes, it will pull 750w. As far as time to heat, if you're heating 10 gallons of water from 70* F to 140* F, the 1000w element will take 1 hr 43 mins. At 750 watts, it'll take 2 hr 17 mins.

 

[sbman]

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.

This is an exact problem I'm thinking about with the solar system on my boat. I'm seriously considering putting the water heater element on a dimmer so I can dial up the wattage I want and set it for the conditions desired at the time I turn it on.

Having max load on your inverter will shorten it's life, unless it's a very good quality one. Cheaper ones aren't designed to output their max load every day for hours at a time. The FETs will overheat and start to fail which increases the heat and makes more of them fail. I would put an older Xantrex Freedom 1000 in the 'marginal quality' range, probably better quality than a new Xantrex though.

 

[O C Diver]

So this element will pull 750w, take 25% longer, but use the same amount of total power to heat a shower?

It takes 33% longer as in my example.

Ted

 

[FF]

Moat HW heaters come with real crap insulation.

Insulation is way cheaper than more batts.

 

[catalinajack]

Moat HW heaters come with real crap insulation.

Insulation is way cheaper than more batts.

Extra insulation is good no matter what. I added half-inch rigid, foil-backed insulation to my square-format heater. Heat retention is great. The outside is barely warm.

 

[ERTF]

This is an exact problem I'm thinking about with the solar system on my boat. I'm seriously considering putting the water heater element on a dimmer so I can dial up the wattage I want and set it for the conditions desired at the time I turn it on.

An alternative option I thought of is to install a programmable switch. So if you have a low wattage element, and need to go somewhere in the morning, you can just set it to run for 2 hours before you wake up. That solves the most common "don't wanna wait 2 hours for hot water" situation.