Fusing an alternator on a house bank

[BjarneK]

Originally Posted by s/v Jedi

Yes, you need a dedicated fuse for the circuit to the alternator. The fuse should be as close to the positive main busbar as possible. This is the closest you can get and it doesn’t even need a cable: https://www.bluesea.com/products/519...k_-_30_to_300A

It has a 10kA interrupt capacity so that’s good enough for the alternator circuit

Attached is my reference diagram showing this alternator circuit (right side of diagram) incl. this fuse. Note that there is a switch near the alternator as well. This is the alternator service switch, which provides safety while working on the engine for maintenance, repair etc. because it’s rather easy to create a short there.

Thanks for your comment. If I read the diagram correctly, the fuse for the alternator is after the class T fuse at the battery. My question is what happens if the class T fuse at the battery blows for a reason unrelated to the alternator, while the alternator is running?

It seems to me that in this case the alternator would still be connected to all the other electronics, but not to any battery. This would create a voltage spike on all the circuits in the diagram since there is no longer a battery present and the current from the alternator has to go somewhere due to the inductance of the alternator stator.

[s/v Jedi]

Originally Posted by BjarneK

Thanks for your comment. If I read the diagram correctly, the fuse for the alternator is after the class T fuse at the battery. My question is what happens if the class T fuse at the battery blows for a reason unrelated to the alternator, while the alternator is running?

It seems to me that in this case the alternator would still be connected to all the other electronics, but not to any battery. This would create a voltage spike on all the circuits in the diagram since there is no longer a battery present and the current from the alternator has to go somewhere due to the inductance of the alternator stator.

When that main fuse blows, it doesn’t matter anymore because you’re probably burning down to the waterline.

The main circuits between batteries and busbars have the biggest diameter cable and the biggest fuse, meaning another fuse has already blown or something is insignificant for this main circuit to be worried about. The only reason for the main fuse to blow is a short circuit at the busbars which is unthinkable while the alternator is charging.

What you need to worry about is the BMS disconnecting the battery to protect it. This is why you find the alternator regulator being enabled/disabled by relays that are controlled by the BMS. These will stop the field current before the disconnect happens.

[rgleason]

Nick, in your diagram after the two bms what are those three devices going to the bus bar?
Also are those three battery monitors #712 icing on the cake, or do you really need them, because you already have the cerboGX and Color50 shown?

I guess you want to monitor the SOC of the AGM and each LFP.

(In my diagram, actually the fuse is 200a for a 160a alternator, belt managed to 100a.)

[s/v Jedi]

Originally Posted by rgleason

Nick, in your diagram after the two bms what are those three devices going to the bus bar?
Also are those three battery monitors #712 icing on the cake, or do you really need them, because you already have the cerboGX and Color50 shown?

I guess you want to monitor the SOC of the AGM and each LFP.

(In my diagram, actually the fuse is 200a for a 160a alternator, belt managed to 100a.)

Attached is a close-up of that part. To the left of each battery is a shunt of a Victron BMV-712 smart. There are two small red wires: shunt B+ Is connected to the positive of cell 4 and shunt AUX is connected to cell 2. For a 24V system it would be cell 8 and cell 4.

In the BMV setup, you select the option for the AUX input to do midpoint monitoring. Now the BMV will keep an eye on cell balance and you can set an alarm for an imbalance more than x mV. I have it at 100mV. It will report statistics on this as well iirc.

Now you have a battery monitor incl. programmable relay to do things like a storage mode where you keep SOC between 50% and 70% etc. The display unit is right next to the remote control RBS switch on the main DC panel (2nd attachment)

The load side of the two shunts are connected to the battery side of a Smartshunt, and the load side of the smart shunt has double cables to the negative busbar to carry the combined load.

The smart shunt is used by the main display on the Cerbo. You configure it for total connected battery capacity, which is for the two batteries together in this diagram. Others have 3 batteries (when your cells are smaller capacity). The SmartShunt AUX port is connected to the start battery positive so that voltage is also reported.

When you switch a battery offline on purpose, you can reprogram the SmartShunt or you can select the BMV of the one battery left online to be used for the Cerbo display. All battery monitors are usable in the Cerbo as long as they are all connected to it.

[Putt-Putt]

I saw this 12 Volt Reference Diagram a few weeks ago and was going to comment but was just too busy at the time. Here it is again on my screen and this time, I have time so here goes.

From what I see all the batteries are 12V and paralleled so the system is all 12v.

If so, then what are the 24V loads in the Distribution Panel?

Similarly the Orion Tr Smart devices are show as 24V input and 12v output. Why?

The answers to both of these is likely a copy over or failure to edit error, so I think it's really just a housekeeping issue that is easily fixed.

Underway the alternator and while at the dock the Multiplus charges the LFP bank and at the same time through the 12-12? Orions the Service bank is charged. My understanding is that the Orions are settable voltage followers, meaning that they do not have any selectable charging profile. This would mean that whatever is selected as the charge voltage is delivered to the AGMs at all times. Is this an acceptable method of charging these AGMs? You could by way of the RBS simply turn the Service Bank off once fully charged and let the LFP bank handle all loads, provided the Orions can supply whatever is connected through them.

I would consider fusing the supply conductors that connect to the 2 fuse boxes on each side of the Orions.

Like Victron stuff, I know next to nothing about BMS's. If I conclude that the 2 small relays control the 12V+ to the 618s Ignition wire and the BMS is controlling the relay's coil, does the BMS somehow know when you turn the engine off and therefore shut down the regulator? If not the regulator will continue to power the field of an idle alternator, unless you open the lower toggle switch.

Then again I could be all wrong!

[s/v Jedi]

Originally Posted by Putt-Putt

I saw this 12 Volt Reference Diagram a few weeks ago and was going to comment but was just too busy at the time. Here it is again on my screen and this time, I have time so here goes.

From what I see all the batteries are 12V and paralleled so the system is all 12v.

If so, then what are the 24V loads in the Distribution Panel?

Similarly the Orion Tr Smart devices are show as 24V input and 12v output. Why?

The answers to both of these is likely a copy over or failure to edit error, so I think it's really just a housekeeping issue that is easily fixed.

Underway the alternator and while at the dock the Multiplus charges the LFP bank and at the same time through the 12-12? Orions the Service bank is charged. My understanding is that the Orions are settable voltage followers, meaning that they do not have any selectable charging profile. This would mean that whatever is selected as the charge voltage is delivered to the AGMs at all times. Is this an acceptable method of charging these AGMs? You could by way of the RBS simply turn the Service Bank off once fully charged and let the LFP bank handle all loads, provided the Orions can supply whatever is connected through them.

I would consider fusing the supply conductors that connect to the 2 fuse boxes on each side of the Orions.

Like Victron stuff, I know next to nothing about BMS's. If I conclude that the 2 small relays control the 12V+ to the 618s Ignition wire and the BMS is controlling the relay's coil, does the BMS somehow know when you turn the engine off and therefore shut down the regulator? If not the regulator will continue to power the field of an idle alternator, unless you open the lower toggle switch.

Then again I could be all wrong!

- the house batteries can be switched parallel and they are 12V in this diagram

- the start batteries can be switched parallel and they are 12V in all the versions of this diagram

- the house batteries can not be switched parallel with the start batteries

- with “24V loads in distribution panel”, do you mean the text above the panel? If so then yes, I have quickly adapted the diagram to 12V. The original drawing has 24V house batteries.

- the Orion Tr-Smart units should be the 12-12 versions.

- no, when charging the house batteries, the Smart Orions will take power from the charge source and convert it to a charging profile for AGM. This is why these units are used instead of an isolator or automatic charging relay.

- the fuse box feeds do not need a fuse, but my diagram shows rather long lines… in reality they sit right next to the busbars.

- the BMS controlled relays can turn the alternator off. This isn’t for shutdown but it is for the case where the BMS will trigger a high voltage cutoff, disconnecting the house batteries from the busbar. This action causes a transient surge from the alternator which finds the batteries it was charging are gone and the surge will probably burn out the rectifier diodes inside the alternator. For this reason the BMS will shut down the alternator just before triggering the HVC.

These relays act on the red wire from the regulator, which is it’s positive power feed. The regulator also has a brown wire from the ignition switch, which is the regular way to turn it on/off. Because of the serious potential damage from a HVC, Balmar has sent out a statement saying that, although the brown wire is the normal way, in this case and for rare occurrences, it’s better to break the red wire to absolutely make sure the field current is killed for sure and a.s.a.p.

The diagram could have the brown ignition circuit as well, but there are many things left out in order to keep it readable.

I am surprised you can read all the small print because many complained they can’t even see what the components are, talking about “blue blobs” etc.

[Putt-Putt]

Ok, that clears that up.

I must have, in my haste looked at the Orion-Tr Dc-Dc Converter, (you know the one that says "Not intended for battery charging") when I reviewed this earlier. The Smart ones are indeed Smart, good choice.

Circuit protection on the branch circuits to the sub panels is always a good choice regardless of conductor length, and is likely required if you want to be Insurance compliant, but it's your boat and a nice one at that.

Is it not the case that when underway the alternator will still see the Service Batteries through the Orions, even thought both BMS's disconnect the house batteries. If so, your diodes should be safe.

[s/v Jedi]

Originally Posted by Putt-Putt

Ok, that clears that up.

I must have, in my haste looked at the Orion-Tr Dc-Dc Converter, (you know the one that says "Not intended for battery charging") when I reviewed this earlier. The Smart ones are indeed Smart, good choice.

Circuit protection on the branch circuits to the sub panels is always a good choice regardless of conductor length, and is likely required if you want to be Insurance compliant, but it's your boat and a nice one at that.

Is it not the case that when underway the alternator will still see the Service Batteries through the Orions, even thought both BMS's disconnect the house batteries. If so, your diodes should be safe.

Here is the relevant section from ABYC E-11:

11.10.1.5.2 Each ungrounded conductor of a branch circuit shall be provided with overcurrent protection at the point of connection to the main switchboard unless the main circuit breaker or fuse provides such protection.

In practical use this means that as long as the main/battery fuse can protect the circuit, you don’t need additional protection. When you maintain cable diameter to support maximum load (fuse/breaker value may be up to 150% of cable ampacity) then it’s just an extension of the main busbar.

[Putt-Putt]

Does your understanding of maximum load (in the case of a dead short) then require the ampacity of the sub panel's supply conductor to be a minimum of 66% of the sum of the 4 fuses feeding the LFP bus? All 4 sources could be at full trot!

[s/v Jedi]

Originally Posted by Putt-Putt

Does your understanding of maximum load (in the case of a dead short) then require the ampacity of the sub panel's supply conductor to be a minimum of 66% of the sum of the 4 fuses feeding the LFP bus? All 4 sources could be at full trot!

No, other branch circuits are not included in that calculation, but both batteries are and this is bad enough because in my case, they have a 300A fuse each, so we need to deal with 600A current, which means our conductors must have a 400A ampacity rating.

For a large system like this it sounds all enormous but it really isn’t that bad because circuits were designed for a maximum voltage drop of 3% which means that for ampacity all circuits are oversized and come into range. Rule of thumb is that you can go half the capacity and still meet the requirements.

In my case, each battery has a 4/0 cable and 300A fuse. The wiring between main busbar and fusebox is 4/0 as well and this means we have an ampacity of 445A. 600A / 1.5 = 400 so we are well within the limit. If I would add a third battery then I need to upgrade the conductors or lower the fuse values. As it is now I can only have 667.5A fused upstream so for 3 batteries with a little imagination I could give each one a 225A fuse but safer would be a 200A fuse for each. This would of course be enough as it becomes 600A in total again just like it is now and adding battery capacity would not be for greater power but for more energy storage.

Am I right that I detect you have a professional background in electrical? I got my license in 1984 but had already switched to electronics, later followed by IT, so it’s all a long time ago for me except for boat system designs

[Putt-Putt]

I also have a relatively large House battery system 2250 Ah @ 12V plus 16 group 24 batteries for start, Gen. Set. and thruster. They are all wet cells although I would not own an 8D. In short we are energy hogs. Despite all of that, with 1600 Hp I can still plane.

I can also safely draw over 500 amps from the house bank for a short time through the inverters if the wife brings aboard her latest hair dryer. But she is worth it and I wouldn't have it any other way.

I don't quite get your "rule of thumb @ half capacity" statement but thats Ok, we can just leave that there. I can say without a shadow of a doubt that 4/0 & I have a long standing and sometimes challenging relationship. Yours is likely similar.

Professionally, I was a Project Manager in the structural design aspects of building construction, nothing to do with electrical. I retired in 2009, happy. I've boated only 50 odd years.

You chose not to comment on my statement a couple of responses back that your diodes would be safe. I wonder why? What did I miss?

[s/v Jedi]

Originally Posted by Putt-Putt

I also have a relatively large House battery system 2250 Ah @ 12V plus 16 group 24 batteries for start, Gen. Set. and thruster. They are all wet cells although I would not own an 8D. In short we are energy hogs. Despite all of that, with 1600 Hp I can still plane.

I can also safely draw over 500 amps from the house bank for a short time through the inverters if the wife brings aboard her latest hair dryer. But she is worth it and I wouldn't have it any other way.

I don't quite get your "rule of thumb @ half capacity" statement but thats Ok, we can just leave that there. I can say without a shadow of a doubt that 4/0 & I have a long standing and sometimes challenging relationship. Yours is likely similar.

Professionally, I was a Project Manager in the structural design aspects of building construction, nothing to do with electrical. I retired in 2009, happy. I've boated only 50 odd years.

You chose not to comment on my statement a couple of responses back that your diodes would be safe. I wonder why? What did I miss?

It’s just because I’ve been retired since 2002 and simply forgot the diodes

The Orions do not offer enough surge suppression to protect the rectifier diodes in the alternator. I suspect Victron did put in some form of surge protection but this would be designed to protect the Orion, not other equipment connected to it.

The alternator can not “see” the batteries at the other side of the Orion’s: it just sees them as a load, while the batteries at the other side see it as a charge source.

Now there’s the question if the load from a DC-DC converter can prevent the transient surge from occurring to start with. I think this is your path of thought. A transient surge is caused by a sudden change in load and it originates from the windings inside the alternator. This change in load is caused by the HVC of the BMS and the only way to avoid that is by heeding it’s warning and stop charging which is likely to prevent it.

There are devices to connect to the alternator to deal with the surge. Balmar sells one for around $25 and there are others offering more extensive protection as well. Some boats install those as their primary protection against HVC induced transients, but I don’t recommend that because these devices are a last resort device, like a fire extinguisher that you hope is never needed because results aren’t guaranteed.

I do recommend surge suppression to be installed aboard boats.

The setup as shown in this diagram is not my preferred way of charging from the alternator. I posted it upon request from CF members who rely on the alternator as their primary charge source. For many, incl. me, solar is the primary charge source and in that case I recommend that the alternator charges the start batteries, not the house batteries. This completely eliminates the issue and no protection is required.

(But other charge sources like solar controllers should still be connected to the BMS to shut them down before HVC so that HVC is prevented and we don’t lose power)

I attached a diagram of my actual installation. It just shows OEM setup of diesel engine as well as genset, with the alternator connected to the starter circuit.

[goboatingnow]

For a alternator spike of any significant voltage to occur two things must be present (a) reasonably high currents and (b) high di/dt. So if the alternator isn’t under significant load then it’s disconnect spike will not be that large for example the typical car style alternator inductance is around 400uH. With the formula “ V = L( di/dt) and typical switch time in 5-30 mS you can see at say 10A , the voltage spike will be reasonably small.

Secondly these advertised alternator protectors do just that Protect the alternator. There’s no guarantee they will do anything to protect other Dc connected electronics at the same time.

[TxCoastSailor]

If your start battery is lead acid you can connect the LFP batteries to the start battery via high current diodes. If there is a spike on the LFP side the diodes will activate and the start battery will absorb the spike.

[Jetx]

Originally Posted by TxCoastSailor

If your start battery is lead acid you can connect the LFP batteries to the start battery via high current diodes. If there is a spike on the LFP side the diodes will activate and the start battery will absorb the spike.

Interesting idea… one that I haven’t seen mentioned before. Can you give an example of what a suitable diode would be?

In normal operation (in the absence of a high-voltage spike), would the diode pass any current from the house battery to the start battery, or would the batteries effectively be isolated unless/until a spike occurs?