ewarnerusa
Helena, Montana
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Pianotuna and Stircrazy, you're giving me hope again! After reading stevenal and your input, as well as rereading the Morningstar manual again for sizing the diversion load, I think a 24V 1000 watt element will work.
The manual goes over the power rating adjustment of ratio of the voltages squared. It also points out that the adjusted lower power also lowers the current it can accept at those voltages and that elements for much higher voltages like 120V will typically require several in parallel in order to accept all of the diverted current. At least that is how I'm reading it, they don't explain it but show the de-rated current in a table and make some statements using those currents when discussing the number of elements needed for a scenario. With a 24V 1000 watt element, I think the math works out OK with just one element. It suggests using 15V as the max battery voltage to use in a 12V nominal system for adjusting power ratings.
https://www.morningstarcorp.com/wp-conte........ds/technical-doc-diversion-manual-en.pdf
* This post was
edited 06/05/23 04:56pm by ewarnerusa *
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StirCrazy
Kamloops, BC, Canada
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Joined: 07/16/2003
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ewarnerusa wrote:StirCrazy wrote:
If that fits it would still be worth it. wouldn't blow it up at any point because of too much voltage. If they are all the same thread even a bit bigger like the 800 or 1000 watt one might be worth a try.
I need to take readings still to confirm, but my hunch is that the element receives full panel wattage at the full potential array voltage (18V?) when it is getting diversion current. Does that change the math?
ya it's not as easy as going if you halve the voltage, you 1/4 the power from the rated input. so if it gets 18V you would end up around 1/2 the power rating (just guessing off the top of my head after just waking up and getting ready for a night shift ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/wink.gif "wink") )
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pianotuna
Regina, SK, Canada
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To do the calculation one needs to know the voltage under load.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.
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ewarnerusa
Helena, Montana
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pianotuna wrote:To do the calculation one needs to know the voltage under load.
I'll do a run soon and measure, but the manual suggests using 15V for a 12V nominal system. It relates it to maximum battery voltage vs array voltage. But I agree, let's see the measured data vs what the manual suggests.
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ewarnerusa
Helena, Montana
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My multimeter is probably the cheapest one you could find, I don't remember where I got but probably Harbor Freight or a department store. It read 1.5 ohms for both the old and new 12V 300 watt element.
My clamp multimeter is also a budget model off Amazon. It measured 0.9 ohm on old 12V 300 watt element and 0.6 ohm on new 12V 300 watt element.
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ewarnerusa
Helena, Montana
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Test is up and running. I disconnected one of the panels so I'm back to 280 watts total solar array capacity. Using the older of my 12V 300 watt elements. Things seem to be working as expected - battery voltage rose until reaching the absorption setpoint and then diversion started occurring while battery voltage remained constant. I took voltage readings on the diversion load and they are unexpectedly low. When battery voltage is 14.5V, the diversion load voltage is 9.2V with about 9 amps being dumped into heating element. It started the day at lower voltage than this and has settled around this value.
SCC is now in float mode (battery at 13.6V) and the diversion load voltage and current remains about the same. I measured voltage at the SCC terminals and at an Anderson quick-connect close to the SCC and both read 9.2V. I measured at the heating element and it was in the 7V range - voltage drop from 8 gauge wire running the entire length of 27-foot TT? Is this what anyone else expected? I thought I'd be seeing battery voltage or even panel voltage. Current at the element measured via clamp multimeter concurs with laptop SCC monitoring software. The diversion load voltage measurements at the SCC also agree with the array/load voltage value reported by laptop SCC software.
Temperature gun said that the wire leads leading into the heating element are 330F. These are the now-exposed wires that cooked off the heat shrink during initial day-long test run where I suspect I was simply putting too much wattage into the 300 watt element.
![[image]](https://i.imgur.com/9dHF7mql.jpg)
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ewarnerusa
Helena, Montana
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Bummer news on the 24V 1000 watt element. I went to test fit it in the hot water tank and it cannot be fully inserted due to obstruction. The exhaust flue inside the tank interferes. So major bummer ![[emoticon]](http://www.coastresorts.com/sharedcontent/cfb/images/frown.gif "frown")
I went ahead with the bench testing to explore the concept. Element was directly connected to 12V battery system to take measurements. I used the wiring I have put in place for diversion load which is about 30' of 8 gauge wire terminating at the outside access of the water heater with an SAE connector. The element is wired up with an SAE connector so I can plug it in at the outside access of the water heater.
Overcast day so solar wasn't contributing much. I think it was about 3 amps during testing.
Measured 10.7 V at the heating element. Battery voltage was about 12.8V and gradually dropping as load pulled it down.
Measured 23 amps with clamp meter at the element
Measured 0.7 ohm resistance for the element
It was heating up, I sure wish I could take it further and use it in the tank. When prepping the connections, I went ahead and slid some of that high temp heat shrink on the wiring in case the original heat shrink cooked off like during the previous test with the 12V 300 watt element. I didn't activate the heat shrink, I was waiting to see what would happen first. It seems like the wire heated up enough to activate it on its own and on one lead it split. I only had things running for 10 minutes or so. I don't know if it would have cooked the original heat shrink or not. The original stuff looks to be in great shape though after the 10 minutes.
![[image]](https://i.imgur.com/ZeDHjM3l.jpg)
![[image]](https://i.imgur.com/M2Qm26il.jpg)
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