question

pmolettiere avatar image

Disconnecting Large DC Loads

Hi! I've been searching here, but haven't found any discussion around this question.

I'm looking at setting up a large lithium house bank on a boat (800Ah) to drive both DC loads and a multiplus inverter and a VE.Bus BMS. I understand that the BMS should be able to switch the load off under certain conditions. The suggested route is to use a BatteryProtect, and the remote option on the Multiplus.

Switching the Multiplus seems straightforward, but switching the large DC load less so. Max DC ampacity for the load is roughly 600A, although the highest current draws are very intermittent — windlass (100A), electric winches (200A x 2). Even so, my understanding is that I need to switch everything off when indicated by the BMS.

The largest constant current ampacity I see for the BatteryProtect is 220A. While some loads are intermittent, when in use, they may be used for minutes at a time, so I think I must remain within the continuous current rating for the Battery Protect.

What's the best way to switch this DC load?

I've considered paralleling several BatteryProtects, both on the load and on the signaling circuits, but I'm currently leaning towards a 600A contactor with 4000A surge rating, despite the appearance that the signal from the BMS will likely need to drive a relay to provide the necessary current to the contactor.

Please advise.

Thanks!

Peter

BMSBattery Protect
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7 Answers
sv-drumbeat avatar image
sv-drumbeat answered ·

@pmolettiere - What did you end up doing to solve this issue if you don't mind sharing?

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Hey! I ended up using a Gigavac MX series contactor, driven directly from the load disconnect on the ve.bus BMS. Works great! They have contactors rated up to 1000A continuous.

https://www.gigavac.com/catalog/power-products/mx-series

Very high quality, great connectors.

The suggested option of controlling the controllers wouldn't have worked without a lot of effort in my case.

I didn't want a latching relay because I wanted to be sure the load disconnect would fail open.


bathnm avatar image
bathnm answered ·

Do you need to disconnect the big loads directly. Do the big loads (winches) have some control circuitry that you can disconnect. Therefore once the control circuit isn't working the large load will not draw.

I'm about to pull the trigger on a Victron based Lithium system and as an example, I will wire the windlass direct to the main DC buss. The low current solenoid control circuit for the windlass will be disabled by the load disconnect. With the solenoid control circuit dead the windlass will not run and therefore although supplied direct will not draw anything.


Have a look at those high power draws and see if you an isolate them through other routes.

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jwfrary avatar image
jwfrary answered ·

How about using a latching relay https://www.bluesea.com/products/7700/ML-RBS_Remote_Battery_Switch_with_Manual_Control_-_12V_DC_500A

should do the job, in the rare circumstances it’s triggered. Just have a button to ‘reset it to on’

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That's a cool option I hadn't seen, thanks! A couple concerns though:

* The switching component should be normally open, and low power when closed. The Blue Sea device looks to be low current when closed, but it's unclear that it would fail open.

* It's max continuous current is 500A, and I'm thinking I need closer to 700A.

What do you think of this contactor?

https://www.gigavac.com/sites/default/files/catalog/spec_sheet/mx110.pdf

Blue sea one is momentarily that’s true but there are timer relays you could use to achieve that function and at least it’s designed for the marine environment. I know a commercial boat they are fitted on which is now been in service 9 years no problems

No experience with the product you linked to but seems nice quality and seals with a deutch plug...nice

I'm using the GX12SA from the same company. Less beefy than the MX110 (I didn't need 1kA).

Build quality is pretty solid for the few that I bought.


aaronsb avatar image
aaronsb answered ·

How many devices on the load side of your battery bank have capactitive circuitry? It may be worthwhile to consider a precharge circuit in this situation as well.


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I don't think any of the ones I'm trying to switch do…

* three large DC motors (windless, two winches)

* A DC subpanel which drives lighting, small pumps, refrigeration compressors, a watermaker (more pumps, some electronics), and electronics.

There is a Multiplus, but this has it's own disconnect circuitry from the VE.bus BMS, so it wouldn't be switched.

My current thoughts are to use this to switch the DC loads:

https://www.gigavac.com/sites/default/files/catalog/spec_sheet/mx110.pdf

Charlie Johnson avatar image
Charlie Johnson answered ·

A quick review of the VE.Bus BMS Data Sheet shows this:

It appears to me that you can wok with the Pre-alarm signal and the delay time between the pre-alarm and load disconnect to gracefully remove power from your heavy loads.


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Hey Charlie,

Yes - this is exactly the output from the VE.bus BMS that I would need to use to drive the switch to disconnect the DC load.

I'm not sure the Pre-alarm helps much, as all I can do with the loads I have is disconnect them.

The main question is what component to use to do the switching.

Unfortunately I do not believe that you can get hold of the VE.Bus BMS which has the pre-alarm. The manuals and data sheets have been updated but the new product isn't available. Been asking as I am about to pull the trigger on a new system.

pmolettiere avatar image
pmolettiere answered ·

Hey Daniël,

Thanks for the answer. A bit more information about the loads in question:

* Several large electric motors (windlass, winches)

* A DC panel, with roughly sixteen breakers, driving everything from 12v lighting, to various pumps, radar, a watermaker, and electronics

AFAIK, there are no "controllers" for these at all, in the way that the Multiplus has a control input to shut it down. I just need to break the DC (positive) supply lines for them.

I expect that I should be able to install some sort of relay (my understanding is that the BatteryProtect is such a relay) or contactor / solenoid to switch these loads. From recent research, most contactors rated at 600A seem to draw a fair amount of current (up to 1A) to hold the circuit open, which would be undesirable.

I don't understand your comment about "when other loads are connected to the same circuit they would need to be fed from another source." Are you saying the loads need to be fed from a different source, or that the relays need to be powered from a different source?

Can you comment on using multiple BatteryProtects in parallel to achieve higher amperage ratings? Can the VE.bus BMS signal multiple BatteryProtects from it's single load disconnect output? This output seems only to be rated at 10mA, which would argue no, unless the BatteryProtects only require ≤ 3.34mA.

I'm just trying to understand Victron's recommendation for disconnecting high current DC loads from large banks of parallel connected batteries.

Thanks,

Peter

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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @pmolettiere

on big loads, your best option might be to 'control the controllers' or disable power to the relay coils of these loads.

This can be tricky, when other loads are connected to the same circuit they would need to be fed from another source.

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