Battery back up for tankless...
- Thread starter Ponchik
- Start date
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
I’m assuming a gas one? It would be a ridiculous size for any length of time for electric. Igniter and exhaust fan shouldn’t be too big of a load, but the run time wouldn’t be all that great because the inverter would be running even when the water heater wasn’t.
Seven-Delta-FortyOne
Goin’ Down In Flames........
- Location
- Humboldt
- Occupation
- EC and GC
Doesn’t need anything special. Gas tankless usually draws about 300 watts for the fan, igniter, and controls.
I believe some of the units have a flow switch that turns the power on when there is water flow.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
I'm back on why it would need a UPS anyway, typically they're only for devices which can't tolerate an outage of any length but only run for 10-15 minutes (enough for short outages or a generator to take over). Is a customer asking for this?
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
They do, but I’m assuming they want it for a backup for an extended amount of time, such as a couple hours or more. Even if the water heater is not used, the inverter will kill the battery fairly quickly.
Frank DuVal
Senior Member
- Occupation
- Electrical Contractor, Electrical Engineer
But the inverter needs to be running to feed this switch to know when there is flow....\
Unless you took the unit apart and rewired it..... Or added an external non-electronic flow switch and wiring....
gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
What's the typical vampire load for an inverter in this service? Consider the limiting case of this being the only load (~300 watts) and the inverter sized appropriately.
I've got a Jackery battery "generator" in my office to run the network, computers, and lights when power fails. They say they can be used as a UPS and mine has about a 1 kw-hr capacity and can output up to 1500 watts at 120VAC. Something like this would probably work, and could just be a plug in solution. Plug the Jackery into the wall, plug the tankless water heat into it. A bonus is you could just unplug it and take it with you if you want to use it for more than an appliance UPS. Take it camping, etc. If you drain it and the power is still out, you'd need to take it elsewhere to charge for 3 hours to get another kw-hr back into it.
You can get these Jackery units in various sizes by both max output power and kw-hr rating. I got mine on a black friday sale and it was $400. Regular price is about $500. Not sure how many watt-hours you would need for that water heater.
You can get these Jackery units in various sizes by both max output power and kw-hr rating. I got mine on a black friday sale and it was $400. Regular price is about $500. Not sure how many watt-hours you would need for that water heater.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Even if there is no load power being drawn, the fact that the inverter is active will drain the batteries. It's referred to generically as the "inverter parasitic load", and should be listed in the UPS specifications or manual. Sometimes also shown as "zero load power" or "idle load power". I've seen as low as 0.2A and as high as 2A, so it's something to consider when selecting a UPS for this kind of application. 2A @ 120V = 240W, which if you have a 300W load to keep alive, is almost doubling the drain on the batteries (or cutting your run time in half).
VirutalElectrician
Senior Member
- Location
- Mpls, MN
- Occupation
- Sparky - Trying to be retired
ok you've got hot...but what about the water?.or is it city water?