Months ago I used a pre-charge resistor as recommended by Will Prowse and others . Worked fine. No spark. My question is .... If i ever disconnect or even switch off my batteries for any period of time would I have to use that resistor again because the capacitors have slowly discharged? Why I ask is I recently I had to disconnect my batteries for a few hours. When I plugged my Anderson connector back together I noticed a small spark. Seems crazy to have a quick, safe disconnect and still have to unbolt cables and use that resistor before you can turn things on again. FYI, My system is kinda small (100AH, 24V Growatt)
Pre-charge resistor seems crazy
- Thread starter JRUD
- Start date
Yes the capacitors will bleed down. Maybe only a few minutes if they have a bleed resister inside. You don't have to unbolt the cables. You just need to somehow jumper some power to the capacitors. Some clip leads and a resistor.
You can also use a small battery pack made from something like 18650 cells. They only supply X amps so you can connect them up with a couple of jumper wires (even without a resistor) and they will charge the caps up in a second or two. Then make your primary battery connection.
curiouscarbon
Science Penguin
- Joined
- Jun 29, 2020
- Messages
- 3,022
FYI XT90 with built in precharge resistor is an option
i love the type with anti spark feature
important to fully plug in
basically on the positive plug it’s two connections in one. the first few mm connect through a resistor, so when you first plug there’s no spark. then like 1mm gap. then the rest is the full on connection.
when it’s plugged in, it will effectively do the entire precharge dance mechanically
anyways just a random option out of left field
the spark puts stress on the hardware, and i personally do put in effort to reduce that to encourage the hardware to last longer, but that’s just convention.
good luck!
i love the type with anti spark feature
important to fully plug in
basically on the positive plug it’s two connections in one. the first few mm connect through a resistor, so when you first plug there’s no spark. then like 1mm gap. then the rest is the full on connection.
when it’s plugged in, it will effectively do the entire precharge dance mechanically
anyways just a random option out of left field
the spark puts stress on the hardware, and i personally do put in effort to reduce that to encourage the hardware to last longer, but that’s just convention.
good luck!
Steve_S
Offgrid Cabineer, N.E. Ontario, Canada
Has it occurred to anyone to just run a wire to a resistor to push-button (momentary) switch connected to the inverter.
Some have a fused resistor just left in place, while others use a timered relay.
Some have a fused resistor just left in place, while others use a timered relay.
Yes, there are several threads about such circuits. For me the real question is, "how often do I disconnect and do I need something that I might use once every 2 or years. I have been thinking about a small portable solution with batteries that can be swapped out. For sure a built in circuit would be great for that. That resistor included in the XT90 is a really nice solution, where that connector is large enough.
Diysolar123
Solar Addict
- Joined
- Feb 28, 2021
- Messages
- 675
most devices that have large capacitor banks include "bleed resistors" to make sure that the caps do discharge when power is cut. This is important as the caps can be dangerous when charged and somebody opens up the box; a capacitor without a bleed resistor can hold a charge for a long time.
A simple box with a momentary push button+resistor and 16awg wire is easy to make and simple to use...
make one, put it in the circuit and suddenly concerns about "disconnects" for whatever reason no longer matter as you have the solution ready to go!
they do make antispark connectors as others have mentioned but I have never seen anything at the level needed for large battery packs.
If you are going to pull more than 30amps just make a precharge box...you can get anti-spark XT connectors upto the xt150 series I think which is made for 8awg wire as I recall.
Thanx all. Lots of good ideas which makes me curious why I've never heard of these things before. Never seen these extra reisitor circuits on any of the schematics
Seems like a nice solution. Does it come in 4ga?. All I see online is 10ga.
Thanx. I think your suggestion is the winner. Easiest fix for me is to run a couple leads from the battery terminals to the bus with everything turned off. I store my resistor in a Ziploc bag taped to the side of my batteries. I'll just add some wire to the bag to keep everything handy.
I did something of the sort. Used a A-B-BOTH-OFF perko switch as a disconnect. I set the resistor up across A to B, B goes to the batter bank. when I rotate it from OFF to A the resistor charges the circuit, then after 10 seconds I rotate one further to B and it’s on. Now my disconnect and reconnect are seamlessly integrated.
Zwy
Solar Wizard
If you want simple, just do what Ian does at the 19:15 mark. Use a pencil.
Rednecktek
Solar Wizard
Yup! I designed my system with a momentary contact switch bypassing the battery breaker with a 100ohm resistor. Painted right on the box is "Step 1: Press for 5sec" so when anyone goes to turn on the power at the camp, it's 4 easy steps labeled in order.
Good idea. My little trailer will be loaned out to relatives and friends so I will be writing lots of signs and even a user's manual. But... Was it Henry Ford who said there was no such thing as foolproof because fools can be so ingenious?
If you have to write instructions, then your system is complicated. I designed my system with my wife in mind. She's smart, but when it comes to camping she's there to relax, not read instructions. There is no need to flip any switches or do anything in my trailer other than use it. I haven't even told her how to read the battery meter.
When it comes to loaning out my trailer, that's not going to happen. Nobody takes care of my equipment like I do. I don't even like hosting people when I'm there. One of my last guests left skid marks in the toilet. He's on the permanent ban list.
When it comes to loaning out my trailer, that's not going to happen. Nobody takes care of my equipment like I do. I don't even like hosting people when I'm there. One of my last guests left skid marks in the toilet. He's on the permanent ban list.
curiouscarbon
Science Penguin
- Joined
- Jun 29, 2020
- Messages
- 3,022
i settle for “fool resistant” lol!
not sure it goes that big; XT150 was mentioned to go to 8ga.
Post in thread 'Inverter capacitor charging spark!'
https://diysolarforum.com/threads/inverter-capacitor-charging-spark.295/post-204613
Thread 'My Push Button Pre-Charger Install for the SW 4024 Inverter'
https://diysolarforum.com/threads/my-push-button-pre-charger-install-for-the-sw-4024-inverter.20426/
here are two other specific posts that have some reference material
Zwy
Solar Wizard
Rednecktek
Solar Wizard
Not really, just unattended for 7+ months at a time, so I need to disconnect the batteries, PV array, and shut off the AIO. 4 steps is pretty darned simple.
There is always going to be Some complexity in a system, you just do what you can to mitigate it. If it was a system that stayed on 24/7/365 then it wouldn't need instructions, and I wouldn't need to make it "Fool Resistant".
Last edited:
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,633
Better yet, help them remember for next time with "negative reinforcement".
An under-rated electrolytic capacitor that gets 48V (or 120 VAC) if they don't precharge inverter capacitors properly?
Samsonite801
Solar Wizard
- Joined
- Oct 15, 2020
- Messages
- 2,994
Doesn't it seem like if the step is really necessary to precharge an inverter, the manufacturer would put that warning/step into their manual for that model?
And then what happens when your BMS decides to turn off on safety protection? You have to add that ritual into your routine every time you reset it?
I don't ever precharge on my own inverters anymore (unless if I were to see it in the manual, which I haven't yet). I used to always do it when I worked with car audio amp installs a long time ago, but at some point I just stopped worrying about it.
I might do it if I am using someone else's equipment, like a borrowed unit or something (except I don't really borrow stuff anymore), but on my own stuff I don't really care anymore, and so far it hasn't bitten me yet.
I do remember doing it on an install I did for a friend while back with his 12v AIMS inverter (more like I didn't have time to read the whole manual, and I had a 12v testlight right there to use as a resistor already so I just did real quick, and since it wasn't my equipment)...
Honestly, I say just read the manual, see if it says they think you should precharge, if not, I follow their routine and wouldn't do it either. Or you can call your inverter manufacturer and ask them if it really matters to them. Seems like if they built it using quality components, then it should be able to resist a potential blowout caused by simply connecting the battery bank, or they would get a lot of come-backs on their warranties (since most people probably don't do it)...
DISCLAIMER: This is me on my stuff, maybe you should keep doing it if you're worried about blowing something up.
And then what happens when your BMS decides to turn off on safety protection? You have to add that ritual into your routine every time you reset it?
I don't ever precharge on my own inverters anymore (unless if I were to see it in the manual, which I haven't yet). I used to always do it when I worked with car audio amp installs a long time ago, but at some point I just stopped worrying about it.
I might do it if I am using someone else's equipment, like a borrowed unit or something (except I don't really borrow stuff anymore), but on my own stuff I don't really care anymore, and so far it hasn't bitten me yet.
I do remember doing it on an install I did for a friend while back with his 12v AIMS inverter (more like I didn't have time to read the whole manual, and I had a 12v testlight right there to use as a resistor already so I just did real quick, and since it wasn't my equipment)...
Honestly, I say just read the manual, see if it says they think you should precharge, if not, I follow their routine and wouldn't do it either. Or you can call your inverter manufacturer and ask them if it really matters to them. Seems like if they built it using quality components, then it should be able to resist a potential blowout caused by simply connecting the battery bank, or they would get a lot of come-backs on their warranties (since most people probably don't do it)...
DISCLAIMER: This is me on my stuff, maybe you should keep doing it if you're worried about blowing something up.
Last edited:
The precharge is to stop arcing on the contactor, nothing to do with the inverter.
(and yes, the contactor will have documented inrush current limits)
Similar threads
