Author Topic: Yet another (Ughh) hot water question...  (Read 412 times)

openplanet

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Yet another (Ughh) hot water question...
« on: April 04, 2019, 12:17:26 AM »
I have two 2kw arrays and two Classics.  In the summer a single array+Classic is sufficient for battery charging.  So for summer I'd like to connect the other array+Classic directly to a hot water heater. 

1. Am I right that this will simplify the configuration (vs leaving both Classics connected to the battery bank)?
2. Can anyone point me to relevant forum posts?  I've hunted for info about this specific approach, without success.

Thanks, as always.

ClassicCrazy

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Re: Yet another (Ughh) hot water question...
« Reply #1 on: April 04, 2019, 12:33:40 AM »
You could hook the second array directly to the hot water heater element  but you will need to make a DC rated temperature control using a temperature control of some sort ( lots of inexpensive ones on ebay ) and you need to use a heat sinked DC solid state relay rated at sufficient voltage and amps to handle the PV current.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

ClassicCrazy

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Re: Yet another (Ughh) hot water question...
« Reply #2 on: April 04, 2019, 12:36:43 AM »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

openplanet

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Re: Yet another (Ughh) hot water question...
« Reply #3 on: April 05, 2019, 04:16:00 PM »
Thank you.

openplanet

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Re: Yet another (Ughh) hot water question...
« Reply #4 on: April 10, 2019, 07:23:41 PM »
Larry--Given that during the summer I don't need my second array for battery charging, is there any reason you can think of NOT to connect it directly to the water heater (w temp control and SSR) rather than involving my second Classic?
Another question: As we all know, PV arrays are not to be disconnected under load.  But in the scenario where the array goes to the hot water tank via a (temp controlled) SSR, doesn't the SSR opening amount to disconnecting the array "under load?"
Thank you.

ClassicCrazy

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Re: Yet another (Ughh) hot water question...
« Reply #5 on: April 10, 2019, 10:24:42 PM »
I think the only reason you don't disconnect the PV under load is because then you will get an arc across the contact points of the switch - or of the end of wires if you pull them apart. You can disconnect PV using DC rated breakers.  A solid state relay is not like a mechanical switch and a DC rated SSR is designed to disconnect DC loads.

I guess if you don't need the PV in summer to take care of your batteries properly there is no harm to run them to water heating instead.

Larry
« Last Edit: April 10, 2019, 10:28:45 PM by ClassicCrazy »
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

Westbranch

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Re: Yet another (Ughh) hot water question...
« Reply #6 on: April 11, 2019, 05:29:21 PM »
how do you get hot water in the winter?
KID FW1811 560W >C&D 24V 900Ah AGM
CL150 29032 FW V.2126-NW2097-GP2133 175A E-Panel WBjr, 3Px4s 140W > 24V 900Ah AGM,
2 Cisco WRT54GL i/c DD-WRT Rtr, NetGr DS104Hub
Cotek ST1500 Inv  want a 24V  ROSIE Inverter
OmniCharge3024  Eu1/2/3000iGens
West Chilcotin 1680+W to come

OffGrid Wanabe

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Re: Yet another (Ughh) hot water question...
« Reply #7 on: April 15, 2019, 03:09:22 PM »
I used a Fotek SSR digital relay dc controlled to switch AC and left the Midnite hooked up to the array and used the Aux 1 in diversion mode to control the digital relay that way my batteries are always charged and I get hot water. I bought the biggest one I could find 80amps and only use 15 amp AC breaker on the 1500 watt 120 ac element but it makes hot water. I know the 80 amp digital is a fake so I oversized it also I have it on a large heat sink and in a metal electrical box I have monitored it for heat and the highest it has got is 90 Fahrenheit.
Good luck
« Last Edit: April 15, 2019, 03:19:35 PM by OffGrid Wanabe »

openplanet

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Re: Yet another (Ughh) hot water question...
« Reply #8 on: May 01, 2019, 11:24:52 PM »
re your suggestion, Larry, to connect array directly to hot water elements (via, of course, appropriate breakers, thermostats, SSRs, etc.) : Wouldn't I harvest more power by routing array > Classic > 48 volt dc heating element than by connecting the array directly to elements rated for the higher voltage of the array...since the Classic is doing MPPT???
THanks

ClassicCrazy

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Re: Yet another (Ughh) hot water question...
« Reply #9 on: May 02, 2019, 12:35:43 PM »
re your suggestion, Larry, to connect array directly to hot water elements (via, of course, appropriate breakers, thermostats, SSRs, etc.) : Wouldn't I harvest more power by routing array > Classic > 48 volt dc heating element than by connecting the array directly to elements rated for the higher voltage of the array...since the Classic is doing MPPT???
THanks

You will put 100% of the available power into heating the water - until it is hot and then it will shut off  if you hook up a PV direct to water heater.
Not sure what you mean by using the Classic to 48v heating element ?  Using the AUX connector to control a DC line output from batteries ?
MPPT gets more power by finding a higher power point of the PV that is above what the battery voltage is.  Different thing than when you are running a load like water heater.

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

tecnodave

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Re: Yet another (Ughh) hot water question...
« Reply #10 on: May 16, 2019, 09:05:47 AM »
@openplanet,

I have just read this thread and what was missed is the fact that a MPPT controller must be connected to a battery to boot up.  It cannot be powered by the p.v. Input!  One of the cautions I read in MidNite literature stress the fact that when powering up battery MUST be connected first, then PV input. I beleive this to be true of most all MPPT controllers. Some can be started with a dead battery, but this must be designed in. This is not implemented in the Classic!  You risk damaging the. Classic by connecting p.v. Input to the Classic and the output directly to the hot water heater element with no battery as you have suggested. I would not try it, I do not think the Classic will even boot and many have advised that battery must be connected first.  I have had situations where my Kid controllers will not boot with a battery with less than 10 volts, I need to jumper in another battery to boot up and then when the Kid sweeps to find the MPP point the battery falls below 10 volts and the Kid goes to sleep. My Classic's are on 24 volt systems that never fall below 24.0 volts.  Bottom line .....way too expensive a box to even try it......... 

EDIT:   I have damaged my original Kid controller twice now after losing connection to battery with full sun and in use, 1 time I fumbled fingered in shut down and touched the PV in breaker with battery breaker on. Kid went back home to Everett for repairs, second time the battery feed wire loosened in the breaker screw and fell out, another trip back home to Everett.  The damage is almost instainious , dead with no response.  They do need a solid connection to battery at all times, I upped my breakers to 40 amp so that the internal current will limit to 30 amps and not trip the breaker on max loading.
« Last Edit: May 16, 2019, 02:40:16 PM by tecnodave »
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

openplanet

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Re: Yet another (Ughh) hot water question...
« Reply #11 on: May 16, 2019, 10:55:31 PM »
Thank you TechnoDave. 
So suppose I use four very low AH 12v AGMs in series for 48 volts as the power source for the Classic.  The question is then: wouldn't heating water via the Classic have a benefit over directly connecting the array (with appropriate controls & breakers) directly to the hot water tank since the Classic would ensure that the array operates at its MPP?  Larry makes the case that a load like a heating element doesn't need the array to operate at MPP, but I don't completely understand why.
Thanks to all for you patience!

tecnodave

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Re: Yet another (Ughh) hot water question...
« Reply #12 on: May 17, 2019, 03:51:44 AM »
Well I do think that more power would be harvested by operating at MPP but do you really need that much power for hot water......mine is dead simple, I bought 3 pallets of Sanyo HIT 200 watt panels at .20/ watt, these are 96 cell panels with a VMP of 53.5 volts, wired two in series , three in parallel, 6 panels to a 120 volt element, 1250 watt, close enough to MPP and hot within an hour.. This bank is also used during very overcast weather to boost output of one of the controllers, I over panel to 150% during the fowl weather and I do not need a generator backup during the storms that wander in from the Pacific Ocean. I can live on 3kw /day easily, I can get that much with no problem even not seeing the sun all day. My generator is very rarely needed to top the batteries.....I do have a diversion setup using a trace C-40 to divert to a dual coil element 24/48 volt , both elements are in same tank. 120 volt element on bottom and dual coil 24/48 volt element on top. Early day direct solar, late day diversion from battery. The controls on the diversion setup are easier.....the C-40 is hacked and controlled by the classic......I lifted the voltage set pots off the board and use a circuit to artificially set the diversion point controlled by the classic. I bought a bunch of original Trace C-40 at auction at a few bucks each. Don't need diversion, I set voltage set point artificially high so that diversion does not happen, logic board controlled by classic. C-40 way cheaper than SSR.  I just like tinkering
#1 Classic 150 12 x Sharp NE-170, 2S6P, 24volt L-16 Rolls-Surette S-530, MS4024 & Cotek ,  C-40 dirv.cont. for hot water
#2 Classic 150 12 x Sharp NE-170, 2S6P, 24 volt L-16 Interstate,Brutus Inv.
#3 Kid/WBjr 4/6 Sanyo 200 watt multilayer 4/6 P
#4 Kid/WBjr 4/6 Sanyo 200 watt multilayer 2S 2/3 P

TimBandTech

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Re: Yet another (Ughh) hot water question...
« Reply #13 on: June 01, 2019, 09:55:23 AM »
The diversion load auxiliary output  in 'Waste Not High'
mode would divert to your heater without any rewiring or manual intervention.
Still, there is design and you've left out a lot of electrical details.
Your bank voltage, your OCV from the arrays, your heating element spec,
your tank water capacity; all of these factors will help to dictate design criteria.

For instance with 4kW of array you could have 4kW of heating element with Waste Not High smartly diverting power and taking perfecly good care of your batteries. Sending 4kW to a tank at 12 VDC is not a trivial matter though. There is no point in sending 4kw to a small tank. All these details matter.


I have two 2kw arrays and two Classics.  In the summer a single array+Classic is sufficient for battery charging.  So for summer I'd like to connect the other array+Classic directly to a hot water heater. 

1. Am I right that this will simplify the configuration (vs leaving both Classics connected to the battery bank)?
2. Can anyone point me to relevant forum posts?  I've hunted for info about this specific approach, without success.

Thanks, as always.
24 SURRETTE 2-KS-33PS 2V 2500AH @48VDC, 7kW STC PV  (three arrays) 3 Midnite Classics, one with Waste Not High diversion driving 3kW of heating element at 48VDC through three SSR circuits, Two 6kW XW inverters