Quick Question - Good Pre-charge Resistor

[nexusjosh]

I thought about adding this to my master thread, but decided against it, as I haven't been able to find the answer to this yet through search, though I could be blind!

I remember that Will always recommends using a Resistor to pre-charge your MPPT's battery lug. What would a good Resistor be for that task? Is there a tool that anyone has made? I know he just holds the Resistor and connects it with his fingers. I'm getting ready to connect my MPPT to batteries for a function test.

 

[Bluedog225]

I think use a light bulb and socket rated for the voltage of your system. It glows bright when precharging then goes dim. Currentconnected.com or hightech labs had a video on this.

Seems cheap, easy, and lets you know if you made a mistake.

 

[nexusjosh]

I think use a light bulb and socket rated for the voltage of your system. It glows bright when precharging then goes dim. Currentconnected.com or hightech labs had a video on this.

Seems cheap, easy, and lets you know if you made a mistake.

Apologies I just realized I got the termology wrong. Not a Capacator, a resistor.

 

[sunshine_eggo]

#2 pencil with both ends sharpened. About 6Ω.

MPPT doesn't need it. Just battery to inverter connection.

 

[Bluedog225]

Ok. I’m not an electrical guy but posting this in case helpful.

 

[Zwy]

Ok. I’m not an electrical guy but posting this in case helpful.

This is the best answer, Dexter did a great job with this video. A 48V light bulb is not required, just use 4 12V bulbs in series.

I'm thinking of pulling the precharge resistor from my setup and installing light bulbs in series.

 

[Bluedog225]

I wonder if a standard 120 volt bulb and socket would serve?

I don’t know how that would affect amps throughput.

 

[sunshine_eggo]

I wonder if a standard 120 volt bulb and socket would serve?

I don’t know how that would affect amps throughput.

Mostly works.

TL;DR

120V bulbs have a resistance that delivers the rated wattage at the rated voltage, i.e., a 60W bulb moves 120V/60W = 0.5A

120V = 0.5 * R, R = 240Ω

HOWEVER, that's the resistance when the wire is white hot. When the wire is cold, the resistance is much lower. It likely wouldn't be a reliable visual indicator though.

 

[nexusjosh]

This is the best answer, Dexter did a great job with this video. A 48V light bulb is not required, just use 4 12V bulbs in series.

I'm thinking of pulling the precharge resistor from my setup and installing light bulbs in series.

Why? My understanding is that you only need to precharge your system one time.

Mostly works.

TL;DR

120V bulbs have a resistance that delivers the rated wattage at the rated voltage, i.e., a 60W bulb moves 120V/60W = 0.5A

120V = 0.5 * R, R = 240Ω

HOWEVER, that's the resistance when the wire is white hot. When the wire is cold, the resistance is much lower. It likely wouldn't be a reliable visual indicator though.

Back to my original question then. For a 48 volt battery system (Apologies didn't specify in the beginning) what would be a good resistor to use?

 

[Zwy]

Why? My understanding is that you only need to precharge your system one time.

If I shut the house system down by tripping my ABB breaker, I need to precharge again.

On my camper, I shut the battery off when not in use to prevent charging to 100% SOC or discharging.

Back to my original question then. For a 48 volt battery system (Apologies didn't specify in the beginning) what would be a good resistor to use?

I run these on all my systems currently. https://www.amazon.com/gp/product/B07KP9GBJJ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

About a 1 amp draw. I=V/R

 

[nexusjosh]

If I shut the house system down by tripping my ABB breaker, I need to precharge again.

On my camper, I shut the battery off when not in use to prevent charging to 100% SOC or discharging.


I run these on all my systems currently. https://www.amazon.com/gp/product/B07KP9GBJJ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

About a 1 amp draw. I=V/R

Thanks! And thanks for the replies! I've ordered those, and will pre-charge when they arrive. I just finished ensuring my 4 batteries are balanced and connected them all to make a single 48V.

Now... I'm unsure if I should make a separate thread, Probably not. I wanted to run my Hybrid Inverter-Charger for a while to test it. Now I'm getting to the part where I'm unsure. Can anyone point me to a post (As I'm sure there is one) I just need the recommended values to put into my inverter/charger for things like max battery charge current, Voltage set-point to switch from grid to off grid mode, boost battery charging voltage, etc. This is all for a 48v system made up of 4 12 volt batteries connected together.

 

[nexusjosh]

Anyone?