Thread: Power Inverter - how to survive crank? - Pyle PINV3

A second battery with battery isolator.

If you have a charge lamp, try the "UIBI" that I've described on mp3car (google "mp3car izu069 uibi).



PS - the cig socket powers off during cranking.

If your battery is strong, you could try direct wiring to the battery thru a relay that is powered by IGN +12V (which stays on during cranking) or a manual switch.
But an auto-isolated 2nd battery is the best option, especially if there's a chance the inverter will flatten your main battery, or if excess cranking, cold weather, or age dips the cranking voltage below the inverter's shut-down threshold.

If you have had an over-voltage shutdown, check your charging voltage, though it may be a short voltage surge that is triggering the shutdown.

I got to learn about relays.

But I will try hardwiring: battery > fuse > inverter ... then see if survives the crank.

For testing only, the fuse is not needed.
But it is essential for permanent wiring, or if your "test" +12V shorts to GND.


The PINV3 uses 2x30A fuses, ie, 60A. Hence at least a 60A rated cable and fuse if driven to full load.

But if less than full load, you could use a smaller feed fuse (eg, 40A or less) so that blows instead of BOTH 30A fuses.



If that works, the adding a relay to power it isn't difficult.
A relay is a bit like a transistor or amplifier - a little current in for lots of current out. But it's a mechanical switch, hence either off or on.

Common automotive relays are 30A.
An "input" coil current of about 60-250mA cause its contacts (switch) to close.
EG - fused battery +12V to relay terminal #30; output #87 goes to the load...
The +12V "on signal" to the coil #86 with the coil's other end #85 to GND.

[ FYI - The latter can be reversed, ie, +12V to #86 and a GND switch to #85.
But there is a convention that #86 is the more positive compared to #85. That is unimportant UNLESS using a relay with an inbuilt diode for spike protection (to prevent damage to OTHER circuits/electronics). But I hate those relays - I prefer to add my own external diode instead.
The heavy contact terminals #30 & #87 can be interchanged, and can connect anything. EG - they might ground a fan or horn which has +12v supplied.
Relays are simple. And robust.
Only this FYI has added confusion.
There are some good animations on the web that explain & show a relay's operation. But it's simply and electro-magnet (the coil; between pins #85 & #86) that pulls-in an arm that connects #30 to #87. ]



Why use a relay? So a small dash switch (or PC, or IGN key etc) can connect the 60A or whatever is needed.
The relay can be near the battery. The only heavy cables are battery+12V to fuse to relay to inverter+12V, and the inverter's GND.
Only light cables are used for the switch to the relay coil.
Hence maximum power (lowest resistance, lower voltage drop), and better safety (no high-current path to the remote switch).

Some inverters have a remote power-on that imitates that function (ie, an internal relay etc).



And the UIBI battery isolator is simply a relay, but its coil is energized (powered) by the alternator's charge-light circuit (aka D+ or L).
Hence when the charge-light extinguishes (because D+ or L goes to +12V; the charge-lamp itself is "ground switched"), the the +12V from D+/L turns on the relay and connects the 2 batteries together.
It's a automated isolator that only connects when the vehicle is charging.
And it's the cost of a relay - provided the alternator can supply its coil current. That's as opposed to voltage sensing or smart isolators that typically cost tens to hundreds of dollars (and have several undesirable features albethey marketed as "advantages" - eg, "priority charging {LOL!}).
The rest is standard dual-battery stuff - ie, a fuse AT EACH battery end, and the cable in between. (Though I recommend self-resetting circuit breakers instead of fuses for up to 50A interconnections. But that's another story.]

Wow! thanks for such a great explanation. Some it goes over my head a little, but I get the idea. Like you said, is matter of researching it some more. Hopefully I free myself again and can finish this project. (I got too many little project)