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Push button for inverter pre charge switch? Momentary switch ok??

Sprks

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Having read @FilterGuy write up on installing a pre charge switch im curious if a momentary switch would be suitable? Or should they be the on-off switch type? AMZ has these "engine start" switches for cheap. 20a or 50a. Screen Shot 2022-05-01 at 6.00.07 PM.png


The big Perko switch is kind of cramping my available space...

Ive a 24V system and im not sure how to size the resistor... ? Also is there a fuse somewhere in this circuit?

Thank you.
 
Since you only need a 10ohm resistor or so and you're only feeding 24v through it, a smaller switch would be fine. You're only talking about 24v/10o = 2.4a of power.
So, what about using a momentary switch? my beginner thinking has me concerned about leaving an on-off switch in the "on" position??
Thanks
 
ahhh.... just found this post... happens evrytime AFTER i pose my question.

 
Yup, Batt Pos -> Switch -> Resistor -> Inverter Pos

Anything rated for over 3a should be fine, 5 if you want to keep it from getting too warm for the 5 seconds you're holding it.
 
I am looking for clarification about precharge circuits.
Most solutions recommend a "manual" delay or with a relay.
What is the problem with an on-off circuit: a resistor bridging the relay contacts, isolation switches or BMS fet (with a 0-I switch that allows the circuit to be shut down for maintenance)?
-After the main circuit is switched on, by the relay, switch or fet, there is hardly any current flowing through the preload circuit! But by leaving it in service, wouldn't we protect the main contacts from the induction choke effect of an untimely cut-off, while benefiting from the precharge?
Two birds with one stone.
Thanks for the answers.
 
I am looking for clarification about precharge circuits.
Most solutions recommend a "manual" delay or with a relay.
What is the problem with an on-off circuit: a resistor bridging the relay contacts, isolation switches or BMS fet (with a 0-I switch that allows the circuit to be shut down for maintenance)?
-After the main circuit is switched on, by the relay, switch or fet, there is hardly any current flowing through the preload circuit! But by leaving it in service, wouldn't we protect the main contacts from the induction choke effect of an untimely cut-off, while benefiting from the precharge?
Two birds with one stone.
Thanks for the answers.
I would welcome knowledge on your question also. I suppose a first question would be, IS there ANY current through this precharge circuit once Inverter has charged? If yes then how much and since the circuit consumes some power (mine is momentary switch with resistor) would that load be sufficient to be considered? Im sure im not seeing this clearly yet... thanks
 
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Thanks for the answer and sorry for the opacity of the description!
- If we insert a very large resistor, the capacitors would theoretically always remain charged and the residual current could be insignificant.
Once the circuit is initiated it is only a holding voltage the current seems to me to be really insignificant, am I wrong?
In concrete terms, the precharge circuit protects all the elements during the charge, but what about the protection of the contacts during a discharge break?
- Do you have an answer concerning the protection that this assembly can bring, for the contacts, during an untimely cut?
Greetings
 
I am looking for clarification about precharge circuits.
Most solutions recommend a "manual" delay or with a relay.
What is the problem with an on-off circuit: a resistor bridging the relay contacts, isolation switches or BMS fet (with a 0-I switch that allows the circuit to be shut down for maintenance)?
-After the main circuit is switched on, by the relay, switch or fet, there is hardly any current flowing through the preload circuit! But by leaving it in service, wouldn't we protect the main contacts from the induction choke effect of an untimely cut-off, while benefiting from the precharge?
Two birds with one stone.
Thanks for the answers.
If you want to leave your caps charged, just reach in there and clip the bleeder resistors. I suggest you leave lot's of room around your charge resistor for a small blaze. Just make sure you use a wire wound resistor or and old sandbox resistor to open up better than a carbon resistor. I've seen them blaze after massive current because if for some reason you turn on your inverter with load, that stupid inverter will think it has battery hooked up (because it is) and off to the races it goes till the fuse (your charge resistor) pops. That will happen if you have your switch on or off.
 
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If you want to leave your caps charged, just reach in there and clip the bleeder resistors. I suggest you leave lot's of room around your charge resistor for a small blaze. Just make sure you use a wire wound resistor or and old sandbox resistor to open up better than a carbon resistor. I've seen them blaze after massive current because if for some reason you turn on your inverter with load, that stupid inverter will think it has battery hooked up (because it is) and off to the races it goes till the fuse (your charge resistor) pops. That will happen if you have your switch on or off.
Thanks for the clarification,
(theoretically...lol) but with a very very high resistance we would only be compensating for the low leakage currents of the capacitors by evacuating the "energetic" problem ?
 
Correct. But that is good? No, that is bad! If you short a charge resistor across your breaker or relay or whatever the inverter will not have to be recharged. That is true. It will still have B+ at the input when you disconnect the batteries. (so you didn't disconnect the batteries). The inverter is still on. Your wife plugs in hairdryer. Resistor goes POP! (you can hear it).
Thanks for the clarification,
(theoretically...lol) but with a very very high resistance we would only be compensating for the low leakage currents of the capacitors by evacuating the "energetic" problem ?
There is more than leakage currents as the caps have to be discharged by some means. The electrical Gods have ruled that if you disconnect power from any "box" ALL potential energy must be removed from the box. If you have power coming in from another source running through relay contacts or something you will kill me if I open the box to work on it and I thought I had the power off. Large capacitors SHOULD have a means of discharging themselves when the power is removed. You can't leave lethal energy in the box for someone to remove and work on it. So if you want to keep the capacitors on when you disconnect the batteries you only need to overcome the discharge rate of the caps ( RC time) probably megaohm. Use a correct 100 ohm 5-1000watt or more charge resistor then sit back and wait for the pop. What you are trying to do is use a megaohm charge resistor shorted across your relay or breaker to remain in the circuit to overcome the rc time of discharge they have for the caps. They are all different and it doesn't matter. If you leave the charge resistor in there and If you have no output on the inverter ,At some point in time the cap will charge up to B+. Your inverter is on. You must remove the charge resistor in order to remove the B+ from the inverter to turn it off. On my homemade amplifier I couldn't turn it on because the 30 amp breaker on the wall would trip everytime. I have garage full of old school parts as I am strickly analog person. I had to put a NO/NC delay on make relay (Old allen bradley) in there with 100 ohm 7 watt precharge because that is what came out of the drawer when I reached in there. I apply power through nc contacts through 100 ohm to caps. After delay NC contacts opens and NO contacts close applying full power to the caps. Now that I think about it I used like a 300 ohm first and the breaker didn't trip on the wall but every light in the house went dim to black so my wife came running out to the garage wondering what I was blowing up THIS TIME so I soldered another one in parallel on it and was done. 150 ohms. 30 years ago.
 
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The inverter is still on. Your wife plugs in hairdryer. Resistor goes POP! (you can hear it).
Not necessarily. A 2000 ohm resister would probably keep the capacitors charged if the inverter is turned off, but at the full voltage of a fully charged 48V battery would only draw 30mA. A 5-watt resistor would handle this easily.

Having said that, your point about a disconnect needing to disconnect all potential is a valid one.
 
Not necessarily. A 2000 ohm resister would probably keep the capacitors charged if the inverter is turned off, but at the full voltage of a fully charged 48V battery would only draw 30mA. A 5-watt resistor would handle this easily.

Having said that, your point about a disconnect needing to disconnect all potential is a valid one.
Sooooooooo..........I can leave my battery disconnect off, plug in a 5 watt 2000 ohm resistor from my battery to the input of an offgrid inverter and plug a hairdryer into the output because it will only draw 30ma. ok. I am getting ahead of myself because I don't have an inverter picked out yet but I assume If I had one, when I remove the battery off grid, a few seconds later some green led will eventually dim and turn off on my inverter. He wants to keep this led lit (Keep the unit on) thus not needing to precharge because he kept it charged with a high ohm resistor not bleeding down his battery. Now plug in a hairdryer inadvertently. Yaq just let the inverter do what it is suppose to do and when you power back up apply a low ohm resistor momentarily before you throw your breaker or contactor back on and don't try to cheat the physics would be my suggestion. Do as you wish.
 
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Sooooooooo..........I can leave my battery disconnect off, plug in a 5 watt 2000 ohm resistor from my battery to the input of an offgrid inverter and plug a hairdryer into the output because it will only draw 30ma. ok. I am getting ahead of myself because I don't have an inverter picked out yet but I assume If I had one, when I remove the battery off grid, a few seconds later some green led will eventually dim and turn off on my inverter. He wants to keep this led lit (Keep the unit on) thus not needing to precharge because he kept it charged with a high ohm resistor not bleeding down his battery. Now plug in a hairdryer inadvertently. Yaq just let the inverter do what it is suppose to do and when you power back up apply a low ohm resistor momentarily before you throw your breaker or contactor back on and don't try to cheat the physics would be my suggestion. Do as you wish.
What is the maximum voltage the resister can see on a 48V system? Answer 60V
What is the current through a 2000 ohm resister when 60V is aplied: Answer I = v/r = 60V/2000ohm = .03A = 30ma
What is the power of 30ma going through a 2000ohm resistor: Answer P=I^2 * R = .03 x .03 * 2000 = 1.8W.

Even a 1000ohm 5W resistor would work.

At 30mA or even 60mA, the inverter will not turn on and if it did it would immediately go into an Under-voltage error. However, if the inverter switch is on there will probably be a voltage drop across the inverter that would reduce the charge of the capacitors. Even then, if the inverter disconnect switch is turned on the resultant surge would be significantly attenuated because of the partial charge.
 
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Should all inverters be precharged or is it only suggested for a minimum established wattage?
Example, would a 1500 or 2000 watt inverter need a precharge.
 
Should all inverters be precharged or is it only suggested for a minimum established wattage?
Example, would a 1500 or 2000 watt inverter need a precharge.
It is true that the smaller inverters will have smaller capacitor banks and therefore it is less of an issue. However, all inverters will have an inrush and will spark when hooked up. The question becomes, what is too much in-rush.

I would certainly put a precharge on any inverter that is 3K or larger. Above that and you are getting into situations where BMS decides it is a short and shuts down. Below 1500W, you are probably OK. Between 1500 and 3000 is a grey zone.

Having said that..... why not always put in a precharge circuit. It is easy enough to do.
 
What is the maximum voltage the resister can see on a 48V system? Answer 60V
What is the current through a 2000 ohm resister when 60V is aplied: Answer I = v/r = 60V/2000ohm = .03A = 30ma
What is the power of 30ma going through a 2000ohm resistor: Answer P=I^2 * R = .03 x .03 * 2000 = 1.8W.

Even a 1000ohm 5W resistor would work.

At 30mA or even 60mA, the inverter will not turn on and if it did it would immediately go into an Under-voltage error. However, if the inverter switch is on there will probably be a voltage drop across the inverter that would reduce the charge of the capacitors. Even then, if the inverter disconnect switch is turned on the resultant surge would be significantly attenuated because of the partial charge.
True. Most inverters have under voltage protection.
 
It is true that the smaller inverters will have smaller capacitor banks and therefore it is less of an issue. However, all inverters will have an inrush and will spark when hooked up. The question becomes, what is too much in-rush.

I would certainly put a precharge on any inverter that is 3K or larger. Above that and you are getting into situations where BMS decides it is a short and shuts down. Below 1500W, you are probably OK. Between 1500 and 3000 is a grey zone.

Having said that..... why not always put in a precharge circuit. It is easy enough to do.
I have a 24v EG4 battery hooked up to a 24v Aeliussine 2000 watt Pure Sine Wave Inverter. The EG4 BMS is so sensitive that even with this "small", 2,000w, inverter it "sees" a dead short and shuts down every time I attempt to connect the inverter. My push-button, momentary switch with 40 ohm resistor, by-pass pre-charge circuit solves the problem as long as the inverter's own on/off switch is set to "off". Sig Solar (EG4 seller) suggests trying a 125A DC breaker as an inverter connect/disconnect switch because it fast snaps into full connect to minimize arcing... instead of the big, slow & sparky, rotary "Kill" switch that I've been using. Breaker arrives tomorrow. I'll see if it allows me to ditch the momentary pre-charge resistor circuit.
 
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