Fusing control circuits -vs- power supply circuits
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Scott SV Tengah
There are two separate issues here:
The first thing I spec'd when I installed my Victron lifepo4 was 3 mega fuses, one per battery pair. Each fuse is big enough to run the bow thruster on its own, in case the other fuses happen to blow. That protects the wiring in case you have a short. The amount of current that a lithium battery can deliver is a blessing if it's used properly and a curse if it's going through an unintended short. The BatteryProtect or low cell voltage disconnect is there to protect the batteries (hence the name Victron gave it). The largest one they make is 220amps, called the BP220. The bow thruster, hydraulic passerelle, a 5kw inverter running multiple appliances will easily fry it. My BP220 lasted for less than an hour after installing it. First time I touched the passerrelle remote control, the BP220 melted. After using lithium for 4 years now, even if Victron or someone else made a 1000amp BatteryProtect, would not install it as I still do not think a blunt load disconnect of all uses is advisable. I would not want to lose nav lights and autopilot just because I didn't top balance for a few months and despite being at 25% SOC, one of my cells dropped below 2.8v and triggered a low voltage disconnect. Or if I'm away from the boat and the bilge pump is running due to a leaking raw water hose with the aforementioned imbalanced batteries, I would rather the pump keep going and kill one of my admittedly expensive batteries versus have the engine room continue to fill with water. -- Scott 2007 A54 #69 SV Tengah http://www.svtengah.com
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Dominique Sery <dominiquesery@...>
Hello David,
I totally agree with you. The Victron Ve-BMS is not a protection for short circuits or overcurrents. Fuses of the appropriate size are installed as close as possible to each 24 volt battery as well as on the devices according to Victron's recommendations. In addition, most circuits have a circuit breaker. Kind regards Dominique
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David Vogel
Hi Dominique,
To reinforce what Olivier says, I am not sure of the wisdom of protecting only the control-side circuits – as, an uncommanded activation of the electrical motors, such as we would see in the case of a short circuit or stuck contact in the control relays, will see the full current being drawn from the lithium batteries – even when the control switch is not activated, and even if the control circuit is disconnected.
To properly protect the (lithium) batteries (and the intervening wires between the battery and load), requires fusing (or circuit breaker, or other protection device) on the main supply cables, located as close to the battery as possible. AMEL elected not to fuse the power cables to the Bowthruster, and some (many?) owners have seen this as a significant shortcoming and installed an appropriate fuse on this circuit. I believe that the risk of failure with catastrophic consequences is increased with lithium batteries that are not fully protected on the load side.
Please, I am more than happy to be corrected on this, and learn, if I am wrong.
With kind regards to you,
David SM#396, Perigee
From: <main@AmelYachtOwners.groups.io> on behalf of "Dominique Sery via groups.io" <dominiquesery@...>
Hello Olivier, Mon anglais n’étant pas fameux, je vous réponds également en français pour éviter toute confusion. From: <main@AmelYachtOwners.groups.io> on behalf of "Olivier Beaute via groups.io" <atlanticyachtsurvey@...>
Hello Dominique,
Your Victron BP220, as it is connected on your pictures, does not protect the batteries against the big loads/amperage. The bus where it is connected feeds only small loads (lights, fridges, solenoids for big loads, autopilot and all the items connected to the galley 24V panel). If you want to protect your batteries from the big loads (bow-thruster, winches, furlers, windlass, etc...), you need to install a battery protector at the source, which means close to the battery bank and using the big 24V positive cable. And if you do that with your BP 220, you will see that it will blow because of the 500amps of the bow-thruster...
Olivier
From: <main@AmelYachtOwners.groups.io> on behalf of "Dominique Sery via groups.io" <dominiquesery@...>
Hello Scott, I confirm that there is no problem with the battery protect 220. I use it as a protection for the whole 24 volts circuit, including the bowthruster (480 A), the windlasses, the electric winches... I installed it in the cabinet above the sink. I put the 24 volt inlet on the Battery Protect inlet and the outlet on the 24 v panel inlet. The BP is controlled by the Ve-BMS. It works perfectly in my boat, it's the relays of the controls of the big consumers that are activated/deactivated so low consumption. I think that the BP 220 is overdimensioned. I had bought it thinking to install it near the batteries but it is not possible, too low power. I hope this will help you. Dominique Some pictures _._,_._,_
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