Questions about DIY Install of Mini-Splits

[Xringer]

Mini-splits with 'Inverter Technology' start their motors slowly with DC pluses.
There is no instant high power surge with inverter tech.
Brushless DC electric motor - Wikipedia, the free encyclopedia

Motor speed control firmware is written so that M/S motors turn on with a 'Soft Start-up'.


So, I think in the case of a modern Inverter mini-split, the 'LRA' is the actual
AC Amps the mini-split system would draw (via the AC to DC converter),
if the motor locked and couldn't turn.

[WyrTwister]

Originally Posted by Xringer

Mini-splits with 'Inverter Technology' start their motors slowly with DC pluses.
There is no instant high power surge with inverter tech.
Brushless DC electric motor - Wikipedia, the free encyclopedia

Motor speed control firmware is written so that M/S motors turn on with a 'Soft Start-up'.


So, I think in the case of a modern Inverter mini-split, the 'LRA' is the actual
AC Amps the mini-split system would draw (via the AC to DC converter),
if the motor locked and couldn't turn.

I am sure you are correct . My 13 SEER mini split has the old technology in which the compressor cycles off & on . So I have no experience with the DC inverter technology .

I have worked with 3 phase AC Variable Frequency Drives . I am guessing the end result is pretty much the same ?

As far as insulating the service fittings and the final few inches of the line set , this is what I used .

https://www.johnstonesupply.com/stor...ep?pID=G21-515

I insulated the small and large lines myself . I could not find a factory made line set in town , in stock .

Before I used the cork tape , the uninsulated large line ( summer operation ) was sweating up a storm . Can not remember if the small one was too ? On mini splits , the expansion device is in the condenser unit , not at the fan coil unit .

By the way , my 13 SEER 12,000 BTU mini split is hooked up with #14/2/WG Romex & feed with a single pole 15 amp circuit breaker ( 120 VAC ) .

God bless
Wyr

[Xringer]

I wonder how much current it takes to actually pop a 15 amp HACR type breaker?

[NiHaoMike]

Originally Posted by Xringer

So, I think in the case of a modern Inverter mini-split, the 'LRA' is the actual
AC Amps the mini-split system would draw (via the AC to DC converter),
if the motor locked and couldn't turn.

Every inverter drive compressor I have come across uses a sensorless drive as it's expensive to add extra sealed passthroughs for the resolver. As such, it would actually draw very little current trying to start a stalled motor, much less than normal operating current. Most likely it's an equivalent for the capacitive inrush.

[WyrTwister]

Originally Posted by Xringer

I wonder how much current it takes to actually pop a 15 amp HACR type breaker?

Reasonable , simple question .

The answer is not quite so simple .

First of all , for continuous load , loads extending 3 hours or longer , or that may extend for that time period . Calculate 80% or the rated amperage for the wire or for the over current device .

80% x 15 amps = 12 amps continuous load .

For non continuous load , m15 amps would be legal , but I would never recommend it .

Now , you have traditional motor start up ( non inverter , soft start , VFD , etc. ) . Wire is sized as stated above . as far as the over current device , when you wade through all the verbiage , it boils down to this .

In a worst case situation , the over current device is allowed to be up sized as much as necessary for the motor to successfully and reliably ride through the motor start inrush .

Lastly , you have instantaneous trip rating . This would be a situation of a direct short to earth ground , hot to neutral or phase to phase ( hot to hot ) .

Different types of fuses and / or circuit breakers are better at dealing with motor inrush , than others . Same for instantaneous trip rating .

Much better to use over current devices for motor applications , that are designed to ride through the inrush , that to use devices that have to be greatly over sized .

HVAC rated circuit breakers should be OK for motor inrush , at least in a residential environment .

All this is rated / calibrated at a " standard " ambient temperature .

My 4 ton central A/C condenser is rated max fuse / circuit breaker 45 amps . Can not remember the min circuit capacity ( which is calculated at 125% of the max running current , to accommodate continuous load ) .

I have 45 amp " slow blow " fuses in the disconnect . Start load is about 45 amps , which falls to around 19 amps or less . It is wired with # 8 copper wire . No problems .

Resistive loads , like resistance heat , or even incandescent lamps , have an inrush , but not as dramatic as motor start inrush . Resistance heat is almost always treated as continuous load , also .

Sorry for being so long winded . :-(

God bless
Wyr

[Xringer]

I've only seen one breaker pop in my life. It was many years ago.
I had one of the breakers labeled badly and I turned off the wrong breaker.

When I started to work on the outlet box, I did a safety check
and deliberately shorted the hot side to ground (the box).
It melted a little bit off my screw driver and popped the 15A breaker..


Before I built my own electronic breakers, I tried using 15 and 10A breakers on a run-away Sanyo.
The Sanyo would shut itself down at around 3.6 kW (15A @ 240vac),
but the breakers never popped..

Those 10 and 15A breakers weren't the HACR type.. They should have popped, IMHO..

[WyrTwister]

Originally Posted by Xringer

I've only seen one breaker pop in my life. It was many years ago.
I had one of the breakers labeled badly and I turned off the wrong breaker.

When I started to work on the outlet box, I did a safety check
and deliberately shorted the hot side to ground (the box).
It melted a little bit off my screw driver and popped the 15A breaker..


Before I built my own electronic breakers, I tried using 15 and 10A breakers on a run-away Sanyo.
The Sanyo would shut itself down at around 3.6 kW (15A @ 240vac),
but the breakers never popped..

Those 10 and 15A breakers weren't the HACR type.. They should have popped, IMHO..

what was the time duration ? 15 amp on a 15 amp circuit breaker ? Theoretically could hold in there for up to 3 hours , depending on ambient temperature .

Some CB's are more magnetically activated , than thermally activated . Those are less affected by ambient temp .

God bless
Wyr

[nokiasixteth]

Waiting on my 220 volt kw meter to come in to check on everything . So far everything is workin good . Only had one prob . Leaked some . But had a kink in the water hose i had cut the hose runnin perfectly. Havin to run ac now been pretty warm now .

[WyrTwister]

Please forgive me , but you completely went over my head concerning the water hose ?

Did you cut up a water hose for the condensate drain ?

God bless
Wyr

[nokiasixteth]

Originally Posted by WyrTwister

Please forgive me , but you completely went over my head concerning the water hose ?

Did you cut up a water hose for the condensate drain ?

God bless
Wyr

Yeah. I had one that the end got cut off. So i just used it. Works good.