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04-02-2025, 06:35
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#16
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Moderator

Join Date: Mar 2009
Location: Denmark (Winter), Cruising North Sea and Baltic (Summer)
Boat: Cutter-Rigged Moody 54
Posts: 35,224
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Re: Inverter Inrush Currents and Lithium Power Systems
Quote:
Originally Posted by Sowilo
Hi Dockhead.
Ahh, Maybe a bit cloudy (sorry for that) but the keyword being "Proper".
What I mean is that once you have choosen a candidate for battery - check that it has a proper BMS. It can be a combination of internal and external units. I think a proper BMS should protect the batteries for over current as well as over/under charging.
For example I have recently seen a Renogy based system that trusted a BMS made of a combination of two, an external system for over- and undercharge - and an internal for over current. Not easy to reset but it works.
If you have Victron batteries and maybe other Victron units a solid choice is a Smart BMS that does it all.
I mean it is not so easy and a misstake can be expensive.
But if I know the battery model I can tell how I think a proper BMS should be set up.
See my point?
Cheers
/D
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Most of us in this forum build our own batteries using prismatic cells and external BMSs. There are two types of those on the Market- those using external contactors, and those with MOSFETs built in. I'm using JK "inverter" BMSs with 200A MOSFETs, which are very popular now. Naturally they protect from overcharging, overdischarging, high and low voltage. They are extensively programmable and communicate with Multiplus, Cerbo, etc. by CANBUS.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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05-02-2025, 19:45
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#17
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Registered User
Join Date: Nov 2015
Boat: R&C Leopard 40
Posts: 1,023
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Re: Inverter Inrush Currents and Lithium Power Systems
As mentioned up thread, the Victron Lnyx BMS has a built in "pre charge" circuit. This is a great feature for those times I isolate the 2 x Mutliplus 3KVA on the DC side. Super easy to watch it work using the Victron Connect app. That's my normal way to disable and enable the House bank.
__________________
-Chris
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05-02-2025, 20:23
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#18
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Registered User
Join Date: Mar 2016
Location: North of San Francisco, Bodega Bay
Boat: 44' Custom Aluminum Cutter, & Pearson 30
Posts: 920
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Re: Inverter Inrush Currents and Lithium Power Systems
I am still learning as I go and have well over 40 hours of study in this conversion.
I have two LiTime 280 Ah 12 volt batteries for the house.
The power went to a Victron Lynx class T power in, then Lynx Shunt VE.Can, last a Lynx Distributor. I am running a 200A class T fuse for each battery.
Inverter:
Victron Energy MultiPlus-II 2X Pure Sine Wave Inverter Charger for 120 amp Battery, 120V, 3000VA 12-Volt
Charging by solar, wind, 120A alternator via a 50A DC/DC charger, and a Honda 2200i generator
Do I need an external BMS? If so what will work with the LiTime batteries.
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Yesterday, 01:05
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#19
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Registered User
Join Date: Mar 2016
Location: San Francisco
Boat: Morgan 382
Posts: 3,630
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Re: Inverter Inrush Currents and Lithium Power Systems
The current isn't only determined by the internal resistance of the batteries, but by the size of the capacitors in the inverter. Larger inverter = larger current. From my understanding, even with LFP it isn't an issue until the inverter is over 3000W. You might get a big spark when you connect the batteries, but no damage.
That said, a precharge circuit is super easy and super cheap. You already have a main battery disconnect switch (if you don't you need one). Across the 2 terminals of the switch, connect a pushbutton and resistor in series. Before turning on the battery, hold the button for about 10 seconds. There are fancier ways to do it where the recharge is automatic and can't be skipped or forgotten, but what I described works perfectly well.
I forget what I selected for a resistor. Maybe 10 ohms and 5 watts. Somewhere around there. Total cost for the button and resistor was around $2.
__________________
-Warren
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Yesterday, 01:44
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#20
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Moderator

Join Date: Mar 2009
Location: Denmark (Winter), Cruising North Sea and Baltic (Summer)
Boat: Cutter-Rigged Moody 54
Posts: 35,224
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Re: Inverter Inrush Currents and Lithium Power Systems
Quote:
Originally Posted by wholybee
The current isn't only determined by the internal resistance of the batteries, but by the size of the capacitors in the inverter. Larger inverter = larger current. From my understanding, even with LFP it isn't an issue until the inverter is over 3000W. You might get a big spark when you connect the batteries, but no damage.. . .
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Big sparks are always some kind of damage, and you can knacker your contactor in short order if you're connecting it that way.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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Yesterday, 03:39
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#21
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Registered User
Join Date: Sep 2014
Location: On the boat
Boat: LAGOON 400
Posts: 2,377
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Re: Inverter Inrush Currents and Lithium Power Systems
According to Victron guidelines, this is not issue if inverter less than 3kw. We have 2kw and lithium and there was no spark at all when connecting.
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Today, 09:39
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#22
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Registered User
Join Date: Dec 2016
Posts: 45
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Re: Inverter Inrush Currents and Lithium Power Systems
Quote:
Originally Posted by Dockhead
Where did you get the idea that anyone is not using a BMS?
My system is built with JK inverter BMS's, two of them, the 200A type.
I'm not aware of any BMS's currently available which have this function. The Lynx one is only for Victron batteries.
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FYI: The REC Active BMS does not have built in pre-charge capability but offers a pre-charge module, controlled by the BMS as an extra. It works fine.
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Today, 09:58
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#23
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Registered User
Join Date: May 2018
Posts: 14
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Re: Inverter Inrush Currents and Lithium Power Systems
Automated Precharge System.pdf
This Automated Precharge system is more expensive but solves most of the problems.
It can be used on 12V, 24V or 48V systems by choosing the appropriate voltage relays.
The Main Contactor should preferably be a low holding current type to reduce power consumption as it will be on all the time the Inverter is on.
This system will work even if you disconnect main Battery power at the Battery and reconnect after service work, the system will precharge then turn power on to the Inverter.
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Today, 10:18
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#24
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Moderator

Join Date: Mar 2009
Location: Denmark (Winter), Cruising North Sea and Baltic (Summer)
Boat: Cutter-Rigged Moody 54
Posts: 35,224
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Re: Inverter Inrush Currents and Lithium Power Systems
Quote:
Originally Posted by omsray
Attachment 298398
This Automated Precharge system is more expensive but solves most of the problems.
It can be used on 12V, 24V or 48V systems by choosing the appropriate voltage relays.
The Main Contactor should preferably be a low holding current type to reduce power consumption as it will be on all the time the Inverter is on.
This system will work even if you disconnect main Battery power at the Battery and reconnect after service work, the system will precharge then turn power on to the Inverter.
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That's elegant.
There would be no parasitic drain with a latching contactor like the Blue Seas ones.
To make it perfect would require one more step -- a circuit to disconnect the contactor in case of power loss on the bus. Then you'd have to reconnect the contactor (activating the precharge circuit).
I think way too fancy for me -- I think I'm find doing this manually.
__________________
"You sea! I resign myself to you also . . . . I guess what you mean,
I behold from the beach your crooked inviting fingers,
I believe you refuse to go back without feeling of me;
We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
Walt Whitman
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Today, 10:41
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#25
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Registered User
Join Date: Dec 2016
Posts: 45
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Re: Inverter Inrush Currents and Lithium Power Systems
Thank you for this. You show the output going to inverter, but I think it would work just as well if the output went to the load bus that feeds the inverter and all other loads. Do you agree?
I think one would still need the manual shut off on the DC feed, just before the inverter, for safety during AC maintenance and for abyc compliance.
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Today, 10:43
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#26
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,956
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Re: Inverter Inrush Currents and Lithium Power Systems
Quote:
Originally Posted by areddon
Thank you for this. You show the output going to inverter, but I think it would work just as well if the output went to the load bus that feeds the inverter and all other loads. Do you agree?
I think one would still need the manual shut off on the DC feed, just before the inverter, for safety during AC maintenance and for abyc compliance.
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I'd want to be able to pre-charge the inverter separately from the rest of the DC bus. Similarly I'd want to be able to cut DC power to the inverter without having to cut off all DC power.
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Today, 10:48
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#27
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Registered User
Join Date: Dec 2016
Posts: 45
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Re: Inverter Inrush Currents and Lithium Power Systems
Can I ask what would be the benefit of being able to precharge the inverter without precharging any other capacitors that might be on the load bus?
I agree that you need to be able to disconnect inverter from DC without shutting down rest of DC. Most surveyors look for a manual switch on the DC supply to inverter which i have.
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Today, 10:58
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#28
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,956
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Re: Inverter Inrush Currents and Lithium Power Systems
Quote:
Originally Posted by areddon
Can I ask what would be the benefit of being able to precharge the inverter without precharging any other capacitors that might be on the load bus?
I agree that you need to be able to disconnect inverter from DC without shutting down rest of DC. Most surveyors look for a manual switch on the DC supply to inverter which i have.
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You'd have to make sure that absolutely everything on the DC bus will remain powered down while pre-charging and that nothing will try to power up when power is provided. So it complicates the power-on process, and for most of the DC loads there isn't any need for pre-charge anyway.
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Today, 11:15
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#29
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Registered User
Join Date: Dec 2016
Posts: 45
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Re: Inverter Inrush Currents and Lithium Power Systems
I guess that the other dc loads, if left on, would pull too much current through the resistor?
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Today, 11:18
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#30
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,956
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Re: Inverter Inrush Currents and Lithium Power Systems
Quote:
Originally Posted by areddon
I guess that the other dc loads, if left on, would pull too much current through the resistor?
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Exactly. And even if the resistor can handle it, the voltage will drop significantly due to the extra load.
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