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Dirk01 · 22-11-2022, 14:05

Quote:

Originally Posted by ahun

We figured you only really have to do the precharge the very first time you power up the inverter. Unless the system is turned off months and months on end the capacitors stay charged up enough without causing any problems when restarting. So it should be anyway.

But he worries about useless power loss most of the day. And I totally agree. I would (and will!) do it the same way!

Just add up all the continuously powered relays and standby losses they produce (not to forget inverters, MPPT controllers, not seperately switched off appliances, etc. etc. etc.) and you will see that you loose the power production from a 330Wpk PV panel per day.

**s/v Jedi** · 22-11-2022, 14:24

Quote:

Originally Posted by Dirk01

Maybe that article gives you some hints for your design?

https://www.sensata.com/sites/defaul...whitepaper.pdf

Please be aware, that due to the added induction of the wiring the voltage on the contacts could reach +70% (or a bit more) of the battery voltage (and some ySeconds later).

Cheers
Dirk

Quote:

Originally Posted by Dirk01

Or you just use this: https://www.rec-bms.com/wp-content/u..._0_Timeset.pdf

And maybe the main contactor should be a toggle version? A permanently ON coil of the main switch draws a lot of juice also. Look at this maybe: https://tbs-electronics.nl/wp-conten...BP-EN-REVB.pdf

A save toggling relay is offered by taoperformance if you only have an ON/OFF switch. You have to get a customer status for login first.

Cheers
Dirk

What do you mean “hints”? I posted the completed and fully functional diagram in the first post of this thread?
What do you mean “buy that”. Why would I buy it from Rec when ai can build it for $7 myself?

My posts are aimed at enabling people to build these things themselves; they are actually anti commerce as manufacturers don’t like me spilling their black box secrets

**s/v Jedi** · 22-11-2022, 14:26

Quote:

Originally Posted by Emmalina

Personally I have a 4 farad cap on my 12v system for this sort of thing a lot easier !

I don’t think you understand what this is about. It has nothing to do with a capacitor on your system. It is for pre-charging an empty capacitor before connecting it to your system.

The document linked by Dirk exactly explains why.

**s/v Jedi** · 22-11-2022, 14:31

Quote:

Originally Posted by ahun

We figured you only really have to do the precharge the very first time you power up the inverter. Unless the system is turned off months and months on end the capacitors stay charged up enough without causing any problems when restarting. So it should be anyway.

It only takes a second pushing the button so why would you take the chance? I found that it differs from one device to another. Some stay charged for longer (think days, not months) and others actually have safety discharge circuits and are empty within a minute.

I recommend to pre-charge every time, even with only minutes apart. There is no downside to following such a discipline.

**s/v Jedi** · 22-11-2022, 14:35

Quote:

Originally Posted by Dirk01

But he worries about useless power loss most of the day. And I totally agree. I would (and will!) do it the same way!

Just add up all the continuously powered relays and standby losses they produce (not to forget inverters, MPPT controllers, not seperately switched off appliances, etc. etc. etc.) and you will see that you loose the power production from a 330Wpk PV panel per day.

Tests on my installation actually show no measurable power loss when the inverters are switched off but still connected to the batteries.

I switch the inverters (and expensive batteries) off the DC busbars during periods of storage, to prevent damage from power surges, near lightning strikes etc. It simply saves lots of money and effort when you don’t need to replace burned out gear

goboatingnow · 23-11-2022, 00:52

Quote:

Originally Posted by Emmalina

Personally I have a 4 farad cap on my 12v system for this sort of thing a lot easier !

Wow the inrush charging that must be ridiculously high

Dirk01 · 23-11-2022, 00:58

Quote:

Originally Posted by s/v Jedi

My posts are aimed at enabling people to build these things themselves; they are actually anti commerce as manufacturers don’t like me spilling their black box secrets

Your approach is good and I learned A LOT from your posts. In this case I don't think that there are black box secrets. As you explained a LFP based system can deliver nearly endless power. The inrush current spike can easily reach one or two KILO amps which is not good for all the involved components.
How pre-charge works and for what it is good to have is quite simple to understand (although a lot of the posts show that a lot of posters didn't understand the background).
These posters especially aren't as expirienced as you are and cannot 1. calculate, 2. build a certain circuit, 3. consider the environment (box, salty air, power resistor, temperature of the resistor, good practice, etc.). For most of them (including me) a system should be bullet proof, easy to adapt etc.. Not to forget that a certified system probably avoids insurance issues if something goes really wrong.
In conclusion: Why to invent the wheel again and again? One spends hundreds of thousands of $$$ for the boat and thousands each month for living on board. Does 100$ really matter? That is only my way of life and for sure does not suits to everybody.

But your post points (again) to something most cruisers do not consider in their system design. With the result of a early failure or at least an avoidable burden for the individual components.

In this sense, thank you very much

Cheers
Dirk

**s/v Jedi** · 23-11-2022, 06:06

Quote:

Originally Posted by Dirk01

Your approach is good and I learned A LOT from your posts. In this case I don't think that there are black box secrets. As you explained a LFP based system can deliver nearly endless power. The inrush current spike can easily reach one or two KILO amps which is not good for all the involved components.
How pre-charge works and for what it is good to have is quite simple to understand (although a lot of the posts show that a lot of posters didn't understand the background).
These posters especially aren't as expirienced as you are and cannot 1. calculate, 2. build a certain circuit, 3. consider the environment (box, salty air, power resistor, temperature of the resistor, good practice, etc.). For most of them (including me) a system should be bullet proof, easy to adapt etc.. Not to forget that a certified system probably avoids insurance issues if something goes really wrong.
In conclusion: Why to invent the wheel again and again? One spends hundreds of thousands of $$$ for the boat and thousands each month for living on board. Does 100$ really matter? That is only my way of life and for sure does not suits to everybody.

But your post points (again) to something most cruisers do not consider in their system design. With the result of a early failure or at least an avoidable burden for the individual components.

In this sense, thank you very much

Cheers
Dirk

I do not agree with your consumerism approach but I thank you for the kind words

In fact, apart for automating these kind if tasks, I don’t think there exists a more bulletproof method than what I came up with. While automation forms most of my professional background, I also did military engineering while I served in uniform and I am convinced that the solution I posted here is better than what REC sells, even when mounted in a hole in a bulkhead.

I know not everyone can calculate or even understand the principles of operation of such circuits, but this is why I post this: they don’t have to. For building this I think that 90% of boat owners can build this. If it was only guys like me then I wouldn’t have to post it.

Emmalina · 23-11-2022, 12:51

Quote:

Originally Posted by s/v Jedi

I don’t think you understand what this is about. It has nothing to do with a capacitor on your system. It is for pre-charging an empty capacitor before connecting it to your system.

The document linked by Dirk exactly explains why.

If you think it is such an issue you could tap it on your start to charge it ! Personally my inverter is always on. Good project but I am a KISS person after a few lightning strikes. Having mounted many inverters can't say the cap issue has ever been raised.

**s/v Jedi** · 23-11-2022, 13:51

Quote:

Originally Posted by Emmalina

If you think it is such an issue you could tap it on your start to charge it ! Personally my inverter is always on. Good project but I am a KISS person after a few lightning strikes. Having mounted many inverters can't say the cap issue has ever been raised.

That’s because you don’t have lithium or you have high resistance. For good lithium installations you get a couple thousand amps inrush current.

**Jammer** · 23-11-2022, 14:15

Quote:

Originally Posted by ChrisOwens

For the cost of a resistor, a zener diode, and a relay, manufacturers could be building this "soft start" feature into the inverter itself. Why don't they?

They would also have to add the series switch, which is the big expensive part.

Victron puts the inverter precharge feature in their Lynx BMS.

team karst · 23-11-2022, 15:22

This attachment arc happened a year ago when i installed new batts. Next time in 5 years i think i will use a length of lamp cord to soften the inrush. No more complexity rqrd. But do agree that huge inrush is not desirable. I and dV dt stuff.

wholybee · 23-11-2022, 16:25

Very well thought out, and the illuminated switch is a nice touch. I did it with just a resistor and button. Outside of testing when I installed it, I have only needed it once. The lamp is a big improvement.