💡 Soft Start Your Inverter | Avoid Mistakes & Ensure Safety When Pre-Charging Using a Light Bulb!

🔌 Soft Start Your Inverter Safely! Learn how to avoid dangerous mistakes and ensure safety when pre-charging your inverter using a Light Bulb! 💡
In this video, we break from the typical method of using a resistor to pre-charge the capacitors in our inverter. Instead, we choose to use a light bulb! The incandescent bulb offers a safer alternative than a resistor in the event that your system has a short circuit (for example, if you've wired your inverter in reverse polarity). Instead of sending a puff of smoke from your resistor, the bulb simply lights up to notify you that something has gone wrong!
In this video we have a system set up using an SOK 48V100-NCBT battery and a 48V Victron Quattro 10K inverter, and we'll be using both a 10W 10 Ohm resistor and a 48V 40W incandescent light bulb as resistors to pre-charge/soft-start the inverter.
🔔 Please Note: This technique is compatible with incandescent light bulbs only... It won't work very well with an LED bulb.
🛒 Browse the Products Mentioned:
SOK 48V100-NCBT Battery - www.currentconnected.com/prod...
48V Victron Quattro 10K Inverter - www.currentconnected.com/prod...

[@HippocratesGarden]

Seems like.. this would be a good feature to have built into the better Inverters.

[@michaelmorris1802]

Well, I have ben using the resistor method since day one in my inverter experience... when I tell most people I do this, they just look at me like I'm crazy. I'm gonna send them all your video. However, I'm probably gonna switch to the bulb. While I am experienced at this point, added safety is never a bad thing. Appreciate you guys doing these video's!

[@CurrentConnected]

Good stuff!!! We appreciate you sharing the video, it helps a ton. Dexter is pretty experienced too but last week he hooked that quattro up in reverse polarity by mistake...that's what inspired him to make this video. Mistakes happen, and it's far better to be safe than sorry no matter how much experience we may think we have.

[@sNEAKYnIGHTmUPPET]

should mention that if you cant find a 48v lamp for this, you could use 4 12v lamps wired in series and the effect will be the same. I have been doing this for years. I have a box of 12v Interior lamps from RV LED conversions that fit the needs perfectly. Incandescent bulbs don't have a polarity to worry about either. 😃 Have fun, Be safe Also, make sure that the inverter is turned OFF. If not, then the capacitors will instantly drain. 😢

[@landonferguson7282]

With the traditional resistor method, the only way to know if you've precharged the capacitors for long enough is to use a current meter. I like that with this method, you get a good visual indicator as to how long you need to precharge the system for, before you make the final connection. One good spot to precharge a system at, is a fuse holder. On small systems I make every connection except for putting the blade fuse in the fuse holder, then I precharge at the fuse holder, then install the fuse.

[@randacnam7321]

120V lamps will work for charging 24V to 48V inverters no problem. They will also work for 12V inverters but you don't have the benefit of the lamp glowing so you know that the inverter caps are still charging. This 12V case is where a lamp rated for 12V to 60V (yes, they exist) is better. Also, using a clear lamp allows for visual inspection of the filament; as well as making sure the filament isn't broken, you know the inverter is safe to connect to the battery bank once the filament stops glowing and this is harder to do with a silica coated or inside frost lamp.

[@repairman2be250]

Thanks for the video. That is actually the better option between resistor and light bulb. You have a visual when the inverter capacitors are charged.

[@tomlee6926]

Excellent video! you took all the mystery out of this tricky topic. You gave practical advice and took the time to explain a bit of the science. Thanks so much.

[@thecalm3409]

Thank you for the tip. Much better than the resistor method.

[@Drdiesel.]

Tried today, excellent result and very happy.

[@AdamDeLay07]

Never thought about that before. Thanks for sharing this tip!

[@boomermatic6035]

I like it, I will be adding this to my setup for sure.

[@SyberPrepper]

Great tip. Thank you!

[@SRQGuitarGuy]

Great tip. I did not have a socket for my old 12V incandescent light so I just soldered two wires to it and gave this a try. It worked just as you showed but mine dimmed much quicker because I only have a 3000 Watt Ampeak Inverter. But the light bulb allows the charge to pass slowly and no SPARK or snap when I connected the Positive line from the inverter to the batteries. Plus this saved me from ordering one more thing from Amazon. Thanks again.

[@RiggerBrew]

Wow - Great Demo!

[@natesdiysolar]

Great idea, not only safer, but provides a visual indication of successful precharge.

[@chrisreynolds6331]

I use incandescent bulbs for this. Nice visual indication of what's happening. A variant of the "dim bulb tester" from my radio and TV servicing days to prevent loud bangs and unfortunate events. Now that we have LFP batteries to play with this safety method has become important again.

[@patricklyons7683]

Great call, haven't seen this method.

[@JPHER217]

Resistors i have heard about but this lightbulb idea of yours seem sweet😃

[@cleversolarpower]

Excellent explanation.

[@GavinStoneDIY]

I like that method. That wouldn’t have occurred to me. Really cool. Thanks

[@ForbiddTV]

Excellent tip, I will try it in the four 16S 304AH battery banks I am presently building.

[@keything8487]

great idea !!

[@nikkithuillier5519]

Thank you very much for such an excellent and clearly explained solution.

[@triumph0675]

Awesome method !!!

[@zaneenaz4962]

Nicely explained.

[@mannymota3442]

Very clever!

[@markaustin6229]

Great idea! Thanks for sharing 😊

[@CurrentConnected]

Glad you liked it! Thanks for watching!

[@Tokyo1991.JL1AJE]

Great tip! Love the fault detect functionality. I have a 4 position battery isolator/selector switch (off/1/1&2/2) that I purchased to allow me to pre charge the inverter caps. Instead of a resistor I’ll be using a 24V lightbulb or 2x12V in series. Clockwise only… 1=pre-charge That’s the idea anyway.

[@antronx7]

Great presentation! Would be nice if inverter had independent digital voltmeter built in to see if the voltage collapses as soon as you remove precharge resistor.

[@jeremydean6103]

Good video

[@michalisgeorgiou257]

Perfect.....

[@swamp847]

Why would Victron not have an inbuilt system to do this as standard ? I have witnessed this large dump have an affect on my battery but also from my shore power side and so started charging up the capacitors with either the 12v solar or 12v dcdc charger on my van system before connecting the battery (which would otherwise trip the BMS). Thank you for showing and sharing the option with the light bulb!

[@stevenpanish1115]

Nice method and very well-done video. I'm about to bring online a Schneider XW-Pro 6.8K inverter on a large LFP bank with JK BMSs. That BMS allows output current to be limited. Do you know if that would be of any utility? Especially since the XW-Pro has no power switch - so I assume the inverter will try to power up during any precharge. Thanks for your work - I'll have to look at your store as well as your other videos.

[@crhees]

You can also use this method to Charge 2 different SOC batteries and bring them to the same level. Allowing the Higher battery to charge the lesser one. When the bulb goes out you know the 2 batteries are at the same Voltage.

[@TK-123]

Just ordered some of those lamps. I just have to remember to place them in a padded sleeve..😂

[@supermo26]

Does a recharge procedure need to be reaccomplished every time battery and breaker is shut off? How do you know when it needs to be done again? How long do capacitors hold their charge?

[@markeh1971]

Hi, most equipment has an inbuilt discharge resistor to reduce the capacitor voltage to zero to make it safe. But not all. This is why you will see them connect the two conductors to reduce it to zero before they touch it. Remember with low voltages you are not conductive but higher ones you are! Take care and be safe M.

[@fisherguy]

Is this something you should do when installing a brand new multiplus?

[@fixtradingconsulting2935]

one more question...i setup a simple precharge circuit with momentary switch, and a bulb/socket from an autoparts store. works well, except i nicked the bulb against something and it shattered. very fragile bulbs. so it got me thinking, why not same setup but use a resistor of the right volts/watts for your battery...but put an LED on there, so the resistor does the limiting of the amps as the capacitors fill up, the resistor is more durable thing probably lasts a lifetime, but then an LED indicator light just to let you know juice is flowing and when it stops. i wonder if the low watts of the LED might keep it lit up a bit too long, not sure if those LEDs would start super bright and dim the precharge is done, etc. but if do-able its a more durable way to use the lights...thoughts?

[@Dylan-tz4pb]

Hey Great Video, Quick question, what does it indicate if my bulb is blinking on and off?

[@Dave_D.]

Does this apply when hooking up charge controllers as well, or just inverters? And the SK48V100 should not need manual charging of the caps, as it is built in (to a limit)?

[@agusbahagia5122]

You call it soft start, I call it smart start 👍🏻

[@CurrentConnected]

Exactly!

[@Steve_Reject]

I do something very similar when I connect my car audio amps when they haven't been powered in a long time. I use a 12v test light and no more spark!!

[@jamesalles139]

yes! the light bulb as ballast

[@Urugami45]

My first thought was "Wow, what did he do to that power resistor to make it smoke like that?" Then I did the math....you were running 230 watts through a 10W resistor. Of course it smoked. Still, good tip; thanks.

[@brianchetelat6601]

Thank you for this video. Would I need to do something similar for my 12V system which consist of the Multiplus 3K and (6) SOK 206A batteries? Is this something I should setup permanently on my Battery Disconnect Switch?

[@ForbiddTV]

That's what I am doing. I would think it would be more convenient that looking for my resister every time I need to turn the battery on again.

[@fredflintstone1428]

Don't the SOK batteries, along with many server type 48V batteries have a pre-charge circuit built in to the battery?

[@szki272]

I used to have a build wire harness I used when powering electrical that I wasn't sure what wire was what. If I put power to the wrong wire the bulb would just light up and not fry. I think for precharging a person could also use a 110v light bulb as it is just a resistor as well.

[@imnguyen6658]

Yes 110v works. Just dimmer

[@brettchaplin9582]

Hi I have a 12v system in my camper, 2x 120 amp lithium batteries. The only thing not connected is the negative to the inverter so I used the light bulb method from negative cable to negative on the inverter but my light just stays on, what am I doing wrong? 2000w inverter and 12v21w globe I'm using. Thanks

[@TsaWind]

Whelp, minus a couple 12v bulbs... I have a camper that I am installing a 48v system into, so doing this exact connection as in the video, ordered some bulbs that matched the camper but 12v bulbs definitely do not work for a 48v connection. As stated in the video, I ordered a 48v bulb now so hopefully no more bright flashes with a pop!

[@mrtechie6810]

Where do you get 48v lamps?

[@CurrentConnected]

You can always put 4x 12v bulbs in series for 48v. We also found that using a 100W 120v incandescent bulb can actually work pretty well!

[@TsaWind]

I actually did rig up 4 of them in series and it worked! I have the right bulb now so it will be easy in the future.@@CurrentConnected

[@kchortu]

oh i am using this

[@lkevonly]

Very educational, thank you! Where do you buy the bulb?

[@ForbiddTV]

It took a bit of looking to find mine, but I bought four of them on eBay, about $6 each in my case.

[@greyMDA]

can i use a 36v bulb for a 48v battery?

[@TK-123]

Question. I have installed two Victron Quattros in split phase configuration for backup power. Does that mean if I have not used the system for let’s say two months that I need to use this pre-charge resistor on both inverters to make it safe?

[@Zorlig]

Only if you've disconnected the battery.

[@adon8672]

Thanks for the video. What happens if one uses a light bulb rated for higher voltage say 240v?

[@CurrentConnected]

It would be very, very slow. A 120v light bulb might work, but a 240v bulb could take a very long time. This is even more true if you are using a 12 or 24v system.

[@adon8672]

@@CurrentConnected Thanks a lot. I appreciate the prompt response.

[@baricdondarion6228]

The leads for me here is that Victron Multiplus uses Chinese capacitors. i could have sworn they used Nippcon of the quality korean caps

[@ccpirogue]

Do we need a resistor when connecting the growatt 3500 to your 48v battery, or can it be connected then turn breaker on?

[@CurrentConnected]

Always better to be safe than sorry.

[@Electronzap]

Wow. Those resistors are way too hot to touch long before they start smoking, so definitely don't want to be touching it when it does. That is a great way to test for shorts.

[@GreekSIMRACING]

Can i use a 3 position switch off,pre charging & on , connecting this lightbulb 💡 so i can pre change my capacitor?

[@markeh1971]

Hi, I like this idea, that way you have to go through pre charge to finally to connect directly. I’ve seen relay based circuits as well, the use of a bulb would give the visual indication that it was working and if a fault condition existed. Take care M.

[@andrewdunham8973]

What size of Anderson connectors are those? They look like SB50 or SB120 but I can't quite tell on my screen here...

[@TK-123]

Looks like SB-175

[@CurrentConnected]

They are SB175. We use them all the time in the R&D department...best thing ever!

[@panospapadimitriou3498]

played with an 24v inverter and no resistors near.. i grabed my 2 spare old 12v lamps from my 40 years old car soldered in series and VOILA 24v load indicator!!! i didnt connected in rush and capacitors discharged a bit and spark made my cable endings ugly...!!! lesson learned. no wait after pre charge

[@ForbiddTV]

You can get 24V DC bulbs too, my military vehicles are 24V systems.

[@panospapadimitriou3498]

@@ForbiddTV its the story of i use what i find on the trunks of my cars and warehouse!!!! i saw many diyers and electricians have a base style multi lamp projects for precharge .. they are dinosaurs in front of any (wanptec for me) powersuply but they are so vintage and gorgeoys... will; make some

[@azpcox]

Quatros don’t have pre-charge resistors built in?

[@JPHER217]

I dont think any inverter has precharge resistor built in. Now i believe almost all server rack batteries that are plug and play have the precharge resistor built in already in the server rack battery.. So this i suppose is more for us diy builders.

[@ja9915]

What socket is that , 1157 12v dc ?

[@ForbiddTV]

BA15d base, like for a1076, 1176 bulb. Two pole bulb, metal base socket is not part of the circuit in this case. I just bought four of them off eBay for the 48V batteries I am building.

[@anthonyanna7595]

I still get the pop when I precharge. I’m trying to get my outback inverter to start up and having issue

[@lazurm]

It could be that your resistor isn't on long enough or it's too small for the load and, therefore, needs to be connected for a longer time. Finally, you may not have a circuit connected.

[@jws3925]

I guess I am a bit "thick" so please explain. You are applying DC voltage to (for instance) the positive lead of the bulb holder and the load (this case the caps in the inverter) to the negative lead from the bulb holder. This, to me, is a pass thru of 12 volts positive with no apparent negative or ground. Why does the bulb light up? It does not have a completed circuit. What am I missing?

[@markrund6292]

The voltage of the lamp is the max potential the lamp can have applied and survive. (The difference between the terminals) The lamp does not care about grounds or negatives. For instance, you could have two leads 20V and 68V and insert the lamp. It would be happy and light up. (48V difference) The reason the lamp lights up is not voltage so much as current. Imagine you have a 48V source that has a tiny current capacity. even though it could supply the voltage, it would not be able to light up the lamp with little or no current. (Also why the lamps brightness diminishes in his demonstration) So, in rough terms, the lamp is lighting up not because of voltage or grounds or plusses and minuses, but due to a current being conducted in its element.

[@markeh1971]

Hi, if you experimented as a youth using an under voltage bulb in the circuit you get spectacular results. Namely is goes bang. The bulb being the right rating voltage make it a safe option with the visual indicator that the voltage across it drops as the capacitors charge up. Eventually the bulb goes out because there is no voltage difference across its connection. Take care M.

[@mrtechie6810]

That's great! But I cannot find 48V lamps. 😢

[@CurrentConnected]

You can use a 120v lamp, it will just take longer. Otherwise put 4x 12v lamps in series

[@greyMDA]

@@CurrentConnectedcan i use a 220v bulb?

[@rubystead6971]

@@greyMDA I tried but it didnt light up a all thought bulb had blown but after checking it was working fine on 220 volts

[@fixtradingconsulting2935]

also, why when you make the connection through the light bulb does the light first light up, but then go dim (indicating capacitors are filling or filled)?? i would have thought you connect the circuit that includes the bulb and the light should stay on after the capacitor are filled. just a lack of knowledge on my end. figured maybe some others might not know the answer either...perhaps.

[@diylithiumguy]

the bulb lights up because of the current flowing through it while the capacitors are charging. As the current falls towards zero, the bulb dims.

[@fixtradingconsulting2935]

gotcha, maybe im still missing something. if i take the bulb, which i did, and connect to the pos terminal and negative terminal of the battery, it lights up fully. doesnt stim stays lit up. typical powering of a load that light. once the capacitors are filled isnt there a complete circuit as well? like i said, must be missing something so i apolize for myself in advance @@diylithiumguy

[@diylithiumguy]

in this video, the bulb is wired in series with the capacitors. Once the capacitors are charged, there is no more current flowing through the circuit. So no lit bulb. If you were to put it in parallel with the capacitors, then it would keep glowing until the battery depleted itself. Hope this helps...@@fixtradingconsulting2935

[@fixtradingconsulting2935]

100% clear. wasnt thinking about series vs parrallel. thx for clarifying! great stuff. @@diylithiumguy

[@diylithiumguy]

no problem! @@fixtradingconsulting2935

[@thepartyhound]

I thought that the Victron inverter/chargers precharged their capacitors when turned on in the "charge" function without the large surge.

[@rubystead6971]

I thought the same but i was also wrong , they dont have pre charge . There must be a good reason why not , Victron are expensive but good so why would they not include something so cheap and simple in their larger Inverters , there has t be a reason for such an obvious omission .

[@Eec2023]

Would be nice to show how to discharge the caps as well.

[@lazurm]

The instruction that answers your question about discharging inverter capacitors can be found at timer 4 minutes of link kzbin.info/www/bejne/kJ3VpaCAh8uGhpo . Basically, you first disconnect the negative cable from your battery terminal, the negative cable that's connected to your inverter on the other side from the battery. Take your resistor and connect it to the negative cable/lead/wire that you just disconnected and touch the open lead to the positive terminal on the inverter. Note, too, that the capacitors will eventually discharge on their own though it can take some time (weeks in the case of very large inverters).

[@ForbiddTV]

@@lazurm Thanks, I watched the video. Seems like he could have just spanned the two terminals on the inverter with the resister directly (after the disconnect of course). Since I use an Anderson connector between the batteries, I could easily do this at the Anderson plug end.

[@TK-123]

Question.

[@GrantM.-gx2kn]

Sorry, dont happen to have a resistor in my pocket at the moment. However, I bet I can scrape together a 1156 or 57 (Chev guys get it). The last time I seen a ceramic resistor like that was on a firewall of a 70's Dodge when I was a teen. Question: Can you hook up 4 X 12 volt automotive bulbs in series to fill a 48 volt inverter? Trust me, the only experience I have is me and Scott in the 60's urinated on a cow fence not realizing it was intermittently active. Wont do that again...ever.

[@CurrentConnected]

You can use a 120v incandescent bulb on a 48v system, it will just be far dimmer than normal and take longer; yes, four 12v bulbs in series will work as well.

[@GrantM.-gx2kn]

So your saying that I can use basically any bulb with a thicker filament to slowly fill the capacitors, even if they dont glow? eg. A 5 watt mini bulb might glow, but a 150 barn burner will work too, but you'll never see it? @@CurrentConnected

[@mrtechie6810]

And if you brush the positive cable across the grounded case: boom!

[@CurrentConnected]

The SOK batteries used in this video are fully differential, I.E. the cases are not tied to either positive or negative.

[@coreybabcock2023]

I shut the BMS off make my connection and turn the BMS back on no sparks

[@CurrentConnected]

Yes but the BMS is getting hammered with a massive inrush current that can cause it to become damaged. Bad practice.

[@coreybabcock2023]

@@CurrentConnected I have the daly 200 amp BMS can set it to handle 600 amps and it never got hot so crazy I think you made a video on that too

[@CurrentConnected]

@@coreybabcock2023 good luck!

[@coreybabcock2023]

@@CurrentConnected thank you but yea I've used the light bulb method before works good too

[@majid_us]

Wow, I am glad that I didn't purchase the SOK batteries, with no built-in current limiting resistors. I guess it wasn't designed by an electrical engineer.

[@CurrentConnected]

They were; the pro version with an LCD has a current limiting circuit. We have customers requesting a better price point with less fluff, and this is the battery for them. If cost is no issue and the features are more important to you, feel free to consider the version with the LCD display

[@majid_us]

@CurrentConnected Most DIY customers never heard of in-rush current/capacitor. You are making more work for yourself by selling the cheaper versions to those customers who may damage the equipment by not understanding how they should power up the equipment therefore resulting in equipment returns and calls to the tech support. I also don't understand why anyone wants to pay for batteries that don't provide closed loop communication with the inverter.

[@CurrentConnected]

@@majid_us And that's why we make videos and write detailed instruction manuals, design some of the most robust BMSs and have some of the best tech support agents in the industry. I'd be curious to hear your opinion on some feature that closed loop communication adds to a system that can't be done with a battery that does not have communications. As far as I know, every 48v inverter in the market supports voltage control while only a small handful support communication.

[@offgridwanabe]

Any new battery should have protection built in.

[@CurrentConnected]

We have two models in this 48v 100ah form factor; one with all the extra bells and whistles and one without; If the extras are worth the price difference to you, we won't stop ya from buying them.

[@sonjakavalut]

The protection should be integrated in inverter, not in battery.

[@offgridwanabe]

@@CurrentConnected How many cold starts is the switch good for?