Inverter to battery
- Thread starter sibaroni
- Start date
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
If powering down you need to dump the capacitors in the Inverter by leaving the inverter ON when you disconnect the battery (or turn off it's BMS if that is possible with yours).
That Spark when connecting batteries, is the Surge that feeds the capacitors before they can start. A BMS usually sees that as a dead short and immediately shuts off to protect the battery. Some BMS have Precharge capacitors built-in while many don't. For those that don't you have to use a Capacitor to pre-charge the capacitors in the inverter... Some folks here have come up with very creative solutions to deal with that.
A Note, if you have more than 1 Battery Pack in Parallel, that surge demand is SHARED between the battery packs. Typically with 2 or more battery packs in parallel, they won't require a pre-charge circuit as they can collectively handle it.
That Spark when connecting batteries, is the Surge that feeds the capacitors before they can start. A BMS usually sees that as a dead short and immediately shuts off to protect the battery. Some BMS have Precharge capacitors built-in while many don't. For those that don't you have to use a Capacitor to pre-charge the capacitors in the inverter... Some folks here have come up with very creative solutions to deal with that.
A Note, if you have more than 1 Battery Pack in Parallel, that surge demand is SHARED between the battery packs. Typically with 2 or more battery packs in parallel, they won't require a pre-charge circuit as they can collectively handle it.
Not sure what you mean by the bit I put in bold?
... but a resistor is just a passive component that is not directional.
MrNatural22
?SW sunshine =⚡️⚡️lit up thru the darkness✌️
Nope either end will work.
GXMnow
Solar Wizard
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In a proper system, you should have a disconnect switch between the battery bank and the inverter. You should be able to connect all the cables with no sparks while the disconnect switch is open (turned off).
Then connect your resistor across the disconnect switch. 30 ohms seems a little high. On a 48 volt system, it will start at a little over an amp and then the current will drop off as the caps charge. That might be enough. I use an 8 ohm resistor, it gives over 4 amps. That is enough to actually turn on the inverter control panel. When I see that light up, I know I can close the disconnect switch safely.
Another good one is using a light bulb. 120 volt bulbs are a bit high on resistance, but do work. Car headlight bulbs are great for 12 volt system, pulling about 5 amps. For a 48 volt system, you will need about 3 in series to keep them from burning out. The fun thing about the bulbs is they will light up and dim out when the caps are charged up. Good visual indicator. I was going to wire one in with a button, but it has been over 2 years since my battery was powered off. It's not something you need to do very often.
Then connect your resistor across the disconnect switch. 30 ohms seems a little high. On a 48 volt system, it will start at a little over an amp and then the current will drop off as the caps charge. That might be enough. I use an 8 ohm resistor, it gives over 4 amps. That is enough to actually turn on the inverter control panel. When I see that light up, I know I can close the disconnect switch safely.
Another good one is using a light bulb. 120 volt bulbs are a bit high on resistance, but do work. Car headlight bulbs are great for 12 volt system, pulling about 5 amps. For a 48 volt system, you will need about 3 in series to keep them from burning out. The fun thing about the bulbs is they will light up and dim out when the caps are charged up. Good visual indicator. I was going to wire one in with a button, but it has been over 2 years since my battery was powered off. It's not something you need to do very often.
hardtop
New Member
Is it bad to spark?
Ampster
Renewable Energy Hobbyist
It can be bad. I once welded the contacts on a contactor by overriding the precharge resistor on an EV conversion years ago. Since then I have avoided big sparks.
GXMnow
Solar Wizard
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The high surge current can do a lot of damage. In the case of a lithium battery with a MOSFET based BMS, it can destroy the protection MOSFETs and you may not even know it as they can fail shorted. Then you no longer have any protection. The current surge is also very hard on the capacitors in the inverter or charge controller etc. I have even seen the surge current burn leads off of components. It is always best to use a pre charge resistor.
hardtop
New Member
I've been using one set of wires to connect and disconnect my charger and inverter. It does spark a bit when connecting, hopefully the BMS can handle it.
