How to connect inverters to two 12 volt batteries separately using a disconnect switch?
I had connected the two positive poles together to the inverter and connected the negative poles to the inverter's negative pole via a circuit breaker. When I switched on the first battery, the inverter switched on correctly. When I switched on the second battery, there was a short circuit and the eight internal fuses blew (oh my goodness!). I had wired and connected the three-way switch correctly. What did I do wrong? (The negative poles are not connected to ground or anything like that in the motorhome.)
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What exactly is that? And what makes you so sure to have done it right?
Map of the whole!
The switchover must not take place overlapping.
Not every change-over switch guarantees this, so that it can happen mechanically conditionally that, during the change-over, the two outputs of the change-over switch come together briefly.
In most cases this is unproblematic – but not so in your:
In such a case, the batteries are switched to parallenge.
If they have different charging levels, a balancing current flows because the fuller battery charges the less full quasi.
This power can become catastrophic in the case of potent batteries (including car batteries), because:
If capacitors or coils are in play, this can also happen by sparks at the switching contacts of a non-overlapping switch if the contact distances are too small.
For this reason, not every switch is suitable for direct current or can only switch a fraction of the current reliably, which it can switch with alternating current and purely ohmic load.
In such cases, a switch is useful in which the switchover takes place over 0: A <-> 0 <-> B
It must be guaranteed that the exits A and B never come together. even if the switch is tightly welded or the like.
Therefore, the switch must also have positive contacts.
So in summary – switch…
…does not switch overlapping or must have forced contacts
… must have sufficient switching capacity to reliably switch at full load
…switch + or switch two poles, not – alone;)
…each battery needs its own fuse in the plus pole and as close to the battery as possible
…it must be from management, etc. It should be ensured that even outside the switch, the batteries cannot come together without suitable securing.
Even if it’s “only” 12V: There are high current strengths in the game, as a result of which it belongs to a person skilled in the art despite low voltage.
If you take off on the 230V side 10A, in the 12V circle it is at least full 192A!! due to change losses a lot more!
These are more amperes than allow the armor locks of a house connection. is thick enough to trigger a fire in fractions of seconds.
Selecting the 12V fuses in such a way that it can be switched off safely with overload and short-circuit and the battery cannot be overloaded is also absolutely necessary with “only 12V”.
Lines, terminals, etc. are also to be designed so that they can withstand the maximum current.
Fire-hot patch – Even hotter than in a house connection box – Please let a skilled person join it!
you must have seen to find out what went wrong.
By the way. I recommend working with multiple batteries always an inverter with 24 or 48 volt input voltage and then two or even four batteries in series.
the lower power required for the same power makes the thing incredibly efficient.
Where you need 70 mm2 cables for 12 volts at 24 volts 16 mm2 and at 48 volts even 4 mm2
the transition resistances to the pole terminals, other clamping connections to the fuses etc. also become less relavat and last but not least the lower currents in the power electronics also contribute to the increase in efficiency.
Another major factor is the inherent resistance of the batteries. when they leave empty, the current-related voltage drop becomes greater. a battery loaded with 300 amperes can be used accordingly, with a 12 volt flat funnel with 3 kW the duchaus can pass, long not unloaded until it takes damage like a 150 ampere or even only 75 ampere.
an inverter with 3 kW should be operated with 24 volts better with 48 volts!
I like to give you a little sample. a 14 meter long copper wire, that is to say the corresponding 7 meter long device connection line with the cross-section of 2.5 mm2 has a resistance of relatively exactly 0.1 ohm.
We operate four 12 volt lamps with 60 watts each.
In the first scenario, we switched 4 lamps in parallel and take a 12 volt battery as a voltage source. 60 watts through 12 volts, which are 5 amperes per lamp. Since we have four lamps in parallel, this means 20 amperes with which we load the line.
according to the ugly formula (U=R*I), the 20 ampere times 0.1 ohm are 2 volts voltage loss. Once again 20 amperes of electricity are required that we heat up in the cable 40 watts!
Puff way!
Now we change the structure and connect two of the lamps in series. two of these rows are connected in parallel. that means we have to do with two strands through which 5 amperes each flow. a total of 10 amperes. We use two series-connected batteries for supply.
So we have 10 ampere times 0.1 ohm, which corresponds to a volt of voltage loss. 10 amperes are… right? 10 watts!
Now we change the structure again, and all four lamps hang into a series connection. Now only 5 amperes! Of course, we need to turn 4 batteries in series to get to the power
Let’s recit again. 5 Ampere times 0.1 Ohm, that’s half a volt lost. 5 amperes are just 2.5 watts that we are still heating!
Think about it.
It is necessary to see the cause of error.