Another inverter install

sqrpeg

I just finished installing a small pure sine wave inverter in our 2018 320S Boondock, and thought I’d share some photos and rationale in the hope it’s useful to others.

The inverter I chose is the 300W Samlex Solar PST-300-12 PST Series Pure Sine Wave Inverter. My wife is a photographer and the inverter will be used to charge camera batteries and to charge/power her high-end graphics laptop (for which a DC-DC adapter with enough wattage is not available).

I installed the inverter in the driver’s side under-bench area - but instead of building a mounting platform around the wheel well as others have done, I built a platform on the inboard wall, behind the LP/CO detector.



For the AC wiring I moved the existing GFCI outlet receptacle to a new electrical box inside the bench area, then reconnected it to the WFCO and to the other AC outlets exactly as before. Then I installed a second outlet receptacle in the original box, but instead of wiring it with romex I used a 14/3 power tool cord (black plug in photo) which we can plug either into the GFCI outlet when we’re on shore power, or into the inverter when we’re boondocking. This gives us a dual-purpose outlet but without any risk of any cross-circuiting. On shore power, all outlets are still GFCI protected. When boondocking, only the bench outlet will be powered (and GFCI-protected) by the inverter, which is really all we need.


(ignore the blue switch in upper right above - part of a different project)



We’re stingy with our 12V usage and don’t plan on drawing more than 130W from the inverter, so for the DC input I just tapped into the existing battery wiring going to the WFCO (using a heavy-duty splicer for the +12V wire) . Our Victron battery monitor shows that under normal/expected loads we’re still well under the 30A max for that circuit, but I will continue to test and check. If amperage limits or voltage drop turns out to be an issue, I’ll consider running dedicated wires to the battery.

As with any T@B mod, it took a while to figure out how to shoehorn everything in, but I’m happy with the result so far. Shakedown cruise is next weekend.

N7SHG_Ham

I have two Samlex inverters (not in Tab currently) and they are good equipment, good choice.

BrianZ

Nice solution, @sqrpeg.  I might consider doing something like this one day, but so far we haven't been gone long enough to even plug in our little inverter.

I wonder if you could hardwire a toggle switch to flip between the two power sources instead of re-plugging each time.  Also wondering if you will ever forget to switch it back to AC, since it would still work on DC when not needed, just wasting energy. 

Cbusguy

@BrianZ  some inverters either come with or have available remote switching,   but I am right there with you on wear on the ac plug.   

klenger

Here's a link to a terrific inverter automatic transfer switch (relay).  I've used a lot of them and never had any problems.  Pretty simple installation.  You can see how I wired mine by clicking on the link in my signature, and then selecting Wiring Diagrams from the top menu.  

https://smile.amazon.com/gp/product/B004S5Y158/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

sqrpeg

I had decided early on that a transfer switch would be overkill (and also too pricey) for this very basic setup, and since our expected usage involves only infrequent switch-overs, I’m not worried at all about wear on the plug or cord.

Also not too worried about forgetting to switch back to shore power AC when available, since we’re always pretty hyper-aware of our electrical situation (plus the inverter will be turned off by default).

I could have upgraded to the 600W Samlex, which includes a port for a remote on/off switch, but again decided it would be overkill and more $$$.

davel4wa

I did some research on this issue of recharging camera batteries in a boondocking situation and it seems like I found chargers for the batteries in question that run from 12V battery power. That would be more efficient than the inverter path although the inverter would lend itself to other uses.

Omniphil

I'm interested in where the inverter is getting its 12 volt battery juice from?

jkjenn

davel4wa said:

I did some research on this issue of recharging camera batteries in a boondocking situation and it seems like I found chargers for the batteries in question that run from 12V battery power. That would be more efficient than the inverter path although the inverter would lend itself to other uses.

I use the 12v battery chargers for my camera batteries but it won't solve for the higher powered laptop.

N7SHG_Ham

@Omniphil, inverters should always be connected direct to battery with correctly sized wire.

Omniphil

N7SHG_Ham said:

@Omniphil, inverters should always be connected direct to battery with correctly sized wire.

But there are batteries wires already running into the wiring area under the seat aren't there?

N7SHG_Ham

I am speaking in general. Are those heavy enough to support the current draw of the inverter? Likely not! If it is a very small inverter, then you may be able to use existing wiring, but you want to make sure it is big enough. Inverter size, input voltage (I assume 12v) length of run all affect wire size. Lots of online tools to help you size wire.

Omniphil

A 1000 watt inverter if run at max would use about 8 amps. I'll have to see what the factory wiring is, but I believe it's 12 gauge, That's rated 20 amps. The inverter would likely only ever see 500 watts at most.

I'd certainly rather run separate cables, I'll have to go take a look at running wires underneath and see if I can keep them out of the way.

plicato

Omniphil said:

A 1000 watt inverter if run at max would use about 8 amps. I'll have to see what the factory wiring is, but I believe it's 12 gauge, That's rated 20 amps. The inverter would likely only ever see 500 watts at most.

I'd certainly rather run separate cables, I'll have to go take a look at running wires underneath and see if I can keep them out of the way.

Hi Omniphil, 

A1000 watt inverter would draw 83 amps from a 12 V battery at full power.  

Power (watts) = voltage (volts) * current (amperes)

According to this site, a more realistic value is about 93 amps.
https://www.batterystuff.com/kb/tools/dc-to-ac-amperage-conversion-run-through-an-inverter.html
One would need 4 AWG cable or better to handle this kind of current.

A 1000 watt inverter could theoretically output 120 VAC at 8.3 amps.
Power (watts) = voltage (volts) * current (amperes)

Omniphil

93 amps! wow, I'm glad you guys are here, my math was way off...
That seems like a heck of alot of amps to pull out of the battery. Tho I suppose its only for short times and I'll not even be using all 1000 watts.

What are you typical AGM batteries going to like for max discharge rates?

Denny16

My 1200 factory inverter has about AWG 4 cables that run through two big cartridge fuses, one for each positive and negative connection, between the inverter and battery, which are in the same area under the rear bunk.  

Here is a photo, inverter in on the partition at the bottom, fuses are to the left of the inverter:

Cbusguy

@Omniphil your math is correct for the 120 volts 1000/120 is roughly 8 amps.   1000/12 volts is 83 amps.....keep in mind that is assuming 100 percent efficiency which doesn't happen.  There are losses in the wiring because of the high amperage and no inverter is 100 percent efficient.

Agm battery's do not like high amp draws and the
inverters maybe a contributing factor to the premature demise of so many tab 400 battery's.