SSR design question

[SolarMusher]

Hi all,
I would like to try different ways to switch a 120Vac secondary inverter to supply a 120Vac water heater. This secondary inverter would be in search mode (VFX3648-6/8 watts) until absorb (Aux1 waste not/SSR) and then supply a 1500W AC element (when available). I don’t like the idea of starting an inverter in search mode directly with 1.5Kw load and would prefer to wake up this inverter slowly with a small 7/13watts light. I’m wondering how to switch this light first and then only after a small delay to supply these 1500watts to the element? I’m thinking to use VFX aux for the light only but obviously I need another SSR to switch it first.
Any other idea greatly appreciated,
Erik

[kitestrings]

Eric,

While this is all doable, I guess I's question why you want to go thru an inverter in the first place.  Why not change the water heater element to DC - they're readily available up to about 1200 watts.  The second inverter and controls would seem to just be just adding unnecessary complexity.  And, you're adding losses through the inverter that are just that; losses that could be converted to Btus.  We use an inexpensive SS relay controlling the element(s) off the stock tank thermostat(s).

If you do go with the 120VAC scheme - and there are time-delay relays - I wouldn't think the inverter would mind at all taking 1500w without the 'warm up'.  It's a resistive load and well within it's capabilities.

Good luck, ~ks

[SolarMusher]

Eric,

While this is all doable, I guess I's question why you want to go thru an inverter in the first place.  Why not change the water heater element to DC - they're readily available up to about 1200 watts.  The second inverter and controls would seem to just be just adding unnecessary complexity.  And, you're adding losses through the inverter that are just that; losses that could be converted to Btus.  We use an inexpensive SS relay controlling the element(s) off the stock tank thermostat(s).

If you do go with the 120VAC scheme - and there are time-delay relays - I wouldn't think the inverter would mind at all taking 1500w without the 'warm up'.  It's a resistive load and well within it's capabilities.

Good luck, ~ks

Hi Kit,
I'm looking on both way to do it.
My current 48V setup is only 4.4kw/240Vac with a 60A charger (magnum 4448AE) and 830Ah/48Vdc battery bank. if I'd add the VFX in the setup it would increase my charge rate to 85A and my gen time would be shorter in winter. It will also give me more room on the magnum when I need to run a small AC in summer (PV array is 3.2kw). Also, VFX/SSR could be off in winter when there's not enough charge time to heat something.
What kind of thermostat are you using? DC? Would you have a link to a good timer relay?
Erik

[zoneblue]

the vfx has a aux on port, why not just use that to turn the inverter and hot water on? if you dont want to hit the inverter so quick, use a time delay circuit. wire the thermostat into the control, then its all low volts/amps.

[TomW]

the vfx has a aux on port, why not just use that to turn the inverter and hot water on? if you dont want to hit the inverter so quick, use a time delay circuit. wire the thermostat into the control, then its all low volts/amps.

Good point!

Just put a normally open relay across that and it will fire up the VFX when you activate the relay.

My VFX's fire up in under a cycle, I think.  No delay a human can detect. Stuff plugged in going from bypass to inverter using the manual transfer switch with the inverter either "on" or in "search" doesn't interrupt power to the devices plugged into the AC Out.

Pretty sure it can cold start into a 1500 watt resistive load no problem.

Tom

[SolarMusher]

the vfx has a aux on port, why not just use that to turn the inverter and hot water on? if you dont want to hit the inverter so quick, use a time delay circuit. wire the thermostat into the control, then its all low volts/amps.

Good point!

Just put a normally open relay across that and it will fire up the VFX when you activate the relay.

My VFX's fire up in under a cycle, I think.  No delay a human can detect. Stuff plugged in going from bypass to inverter using the manual transfer switch with the inverter either "on" or in "search" doesn't interrupt power to the devices plugged into the AC Out.

Pretty sure it can cold start into a 1500 watt resistive load no problem.

Tom

Tom, my concern with cold start to load is more when cloudly with several "cold starts". I have two sceptic pumps that can start at any time in the night when the Magnum is in search and that has never been a problem, but it's only once in a while.
Zoneblue, I did some research on "time delay circuit/relay" but did not find anything really helpful, would you have some links to share?
Erik

[zoneblue]

A 30 cent 555 timer circuit should be all you need. If you cant build something like that head down to jaycar/radioshack/ebay and buy one assembled. Classic aux port turns on the vfx, and starts the timer. When timer completes turns on the relay to power up the  ssr/hwc.

But i agree with Tom, why not check with outback (or boB and Robin) if it will power up loaded happily.