MPPT to Batteries Circuit breaker.

[GreenWave]

Originally Posted by Senojev

Not be contentious but a fuse is not “required”. ABYC states “overcurrent protection device” and goes on to give the options of a breaker or fuse.

so noted

[Stu Jackson]

Originally Posted by Celestialsailor

Also, I guess it would not be a good idea to wire the MPPT to the battery switch. But to the house batteries directly. And if I want to charge up my starter battery, I could switch my battery switch to "Both" and charge it that way. Does that sound feasible?

Yes. Just like any other single output charging source, of course depending on how it's wired.

[Statistical]

Originally Posted by Senojev

Comment 2) does not apply just to LiFePO4, it applies to any large bank.

Very true I worded that badly. All fuses should have appropriate AIC but the very high short circuit current of LFP cells means that generally speaking you are going to need a Class T fuse (or something with even higher AIC). Lead Acid batteries due to the higher internal resistance still should have appropriate AIC but it being a lower value means more fuse types are acceptable.

[s/v Jedi]

Originally Posted by Senojev

If you are using 10AWG yes but using 10AWG is a mistake. You should be using 6AWG to get a voltage drop of around 3%. With 10AWG you are giving away almost 1V. That’s why S/v Jedi says to use 6AWG and a 60A fuse. I prefer a good quality breaker but others prefer fuses.

Exactly.

It doesn’t matter how much current there is between solar panels and the controller; that is a different circuit. Between controller and battery you have the battery charge current that can be up to 40A. To limit cable losses, this should be an AWG 6 cable and the rule of thumb fuse value is 1.5x maximum of 40A so that is 60A. The AWG 6 can handle 120A (with big losses) so at half of that we have plenty safety margin.

For fuses, I use a fuse box but you can use MRBF fuses as well, like these: https://www.bluesea.com/products/215...k_-_30_to_300A

I use these: https://www.bluesea.com/products/cat...ocks/SafetyHub

[SunnyIsleMark]

Originally Posted by Celestialsailor

Also, I guess it would not be a good idea to wire the MPPT to the battery switch. But to the house batteries directly. And if I want to charge up my starter battery, I could switch my battery switch to "Both" and charge it that way. Does that sound feasible?

I’d suggest you do a bit more research here…controllers are not usually set up to charge dual battery banks in parallel, especially if they are different types/capacities. There are options, but require more hardware.

[Celestialsailor]

Thanx everyone, I'm glad I posted this. I will take all this advice and be able to sleep at night...

I would also like to confirm that if the MPPT feeds the house bank, that by switching the battery bank selector to both will flow a charge into the starter battery as well.

[Stu Jackson]

Originally Posted by SunnyIsleMark

I’d suggest you do a bit more research here…controllers are not usually set up to charge dual battery banks in parallel, especially if they are different types/capacities. There are options, but require more hardware.

It still amazes me how much misinformation gets written almost matter-of-factly




Why not? Most house banks ARE parallel batteries. While correct about different types, only (not especially) if their charging requirements are different (i.e., AGM and FLA are very very similar). The B position on a 1-2-B switch stands for both, which means parallel, and requires no more hardware. Controllers don't know what's downstream of them.


The real issue is any voltage sensing, but the OP is asking if could do this on a limited, controlled manner. Not an issue, I believe. Just dump a few amps into the reserve/start bank.

[thomm225]

Originally Posted by Senojev

Not be contentious but a fuse is not “required”. ABYC states “overcurrent protection device” and goes on to give the options of a breaker or fuse.

Right.

I still haven't added a fuse to my Victron 75/15 MPPT Controller or any of the other 5 PWM Controllers I have used since 2011 but may at some point.

I only have 115 watts of panels feeding my two 6 volt 220 ah batteries at this time so not a lot of current.

Using 14 Gauge Wire from the controller to the batteries. 10 and 14 Gauge from the panels to the controller.

My old 65 Watt Panel faces straight up as it is on the Aft Lazarette and the Renogy 50 Watt to the side. I rotate it as necessary to face the Sun.

Neither is hard mounted.

[s/v Jedi]

Originally Posted by thomm225

Right.

I still haven't added a fuse to my Victron 75/15 MPPT Controller or any of the other 5 PWM Controllers I have used since 2011 but may at some point.

I only have 115 watts of panels feeding my two 6 volt 220 ah batteries at this time so not a lot of current.

Using 14 Gauge Wire from the controller to the batteries. 10 and 14 Gauge from the panels to the controller.

The fuses are not for the current coming from the controller; they are for the current that can come from the battery in case of something bad happening to a controller. This is why the fuse is as close to the battery as possible and why it is rated for the wiring used.

[Senojev]

Although the current from your controller is small, you still need to protect the cable if a short develops between the battery and the controller to prevent the cable from becoming overheated and burning. Have you ever touched a wrench to both positive and negative terminals? Not fun, especially if it welds itself!

Please add a fuse of the appropriate size as close to the battery as you can, ideally within 7” or if not possible a max. of 40” and cover the cable with protective wire loom.

End of PSA!

[thomm225]

Originally Posted by s/v Jedi

The fuses are not for the current coming from the controller; they are for the current that can come from the battery in case of something bad happening to a controller. This is why the fuse is as close to the battery as possible and why it is rated for the wiring used.

That makes sense although a bit far fetched.

You wouldn't want a fire offshore though so I have ordered these inline fuse holders w/fuses.

https://www.amazon.com/MulWark-Inlin...zcF9hdGY&psc=1

To be installed before I round the Outer Banks. Or sooner...

You never can tell though.

We had a 28 volt/125 Amp Power Supply that was being pulled down by shorted wires just last week. The wire bundle had been up against the Rudder Pedals adjuster.

https://www.bellnw.com/products/ametek-dlm-32-125e

You can adjust the rudder pedals on this aircraft to suit you as the pilot.

Over the years the wire bundle covering got worn off then 2 wires had gotten exposed after the insulation on them got worn through.

Took us hours to figure it out as this power supply didn't crowbar but would come back on as soon as it's overcurrent protection current dropped the voltage down far enough. I hadn't seen that before so was observing the troubleshooting.

We rarely get old school problems these days.

So the cockpit lighting and Instruments would cycle on and off continuously. Techs finally started disconnect Phoenix I/O Module Banks then individual Instruments until the problem stopped.

The wires had shorted out to an Instrument's Metal framing.

It powered the Phoenix I/O which powered all the Instruments in the Cockpit.

[SunnyIsleMark]

Originally Posted by Stu Jackson

It still amazes me how much misinformation gets written almost matter-of-factly




Why not? Most house banks ARE parallel batteries. While correct about different types, only (not especially) if their charging requirements are different (i.e., AGM and FLA are very very similar). The B position on a 1-2-B switch stands for both, which means parallel, and requires no more hardware. Controllers don't know what's downstream of them.


The real issue is any voltage sensing, but the OP is asking if could do this on a limited, controlled manner. Not an issue, I believe. Just dump a few amps into the reserve/start bank.

Thanks for the rude response to my well intended comment, but I stand by my suggestion.
You have touched on a couple of the reasons why both more information and more research is warranted. Amount of relative depletion is another.
But I’m done here.

[thomm225]

Originally Posted by thomm225

That makes sense although a bit far fetched.

You wouldn't want a fire offshore though so I have ordered these inline fuse holders w/fuses.

https://www.amazon.com/MulWark-Inlin...zcF9hdGY&psc=1

To be installed before I round the Outer Banks. Or sooner...

You never can tell though.

We had a 28 volt/125 Amp Power Supply that was being pulled down by shorted wires just last week. The wire bundle had been up against the Rudder Pedals adjuster.

https://www.bellnw.com/products/ametek-dlm-32-125e

You can adjust the rudder pedals on this aircraft to suit you as the pilot.

Over the years the wire bundle covering got worn off then 2 wires had gotten exposed after the insulation on them got worn through.

Took us hours to figure it out as this power supply didn't crowbar but would come back on as soon as it's overcurrent protection current dropped the voltage down far enough. I hadn't seen that before so was observing the troubleshooting.

We rarely get old school problems these days.

So the cockpit lighting and Instruments would cycle on and off continuously. Techs finally started disconnect Phoenix I/O Module Banks then individual Instruments until the problem stopped.

The wires had shorted out to an Instrument's Metal framing.

It powered the Phoenix I/O Module that powered that Instrument in the Cockpit.

Correction.

Took us hours to figure it out as this power supply didn't crowbar but would come back on as soon as it's overcurrent protection dropped the current down far enough. I hadn't seen that before so was observing the troubleshooting.

[Stu Jackson]

Originally Posted by s/v Jedi

The fuses are not for the current coming from the controller; they are for the current that can come from the battery in case of something bad happening to a controller. This is why the fuse is as close to the battery as possible and why it is rated for the wiring used.

Originally Posted by thomm225

That makes sense although a bit far fetched.

>>>>>>

jedi,


I guess thomm225 still hasn't gotten the Memo about his battery bank, however small it may be, is just a BIG BOMB waiting to go off and the only protection is that fuse he thinks is far fetched.


Heck, decades ago when somebody explained it to me that way, I hastened to listen and understand.


Anybody who still doesn't "get it" and thinks the fuse is only to protect the equipment downstream oughta get the Memo, too.

[capt jgw]

Yeah that's not far fetched at all. If the wires or controller short out, you need a fuse in there. One might get confused thinking the controller is a power source so the fuse goes on that end. You could put a fuse on both ends but lacking that, put it at the bigger source end. A battery capable of putting out maybe 1000 amps in a short or the controller at 20 amps? It goes at the battery end. And again it's perfectly ok to fuse at below the wire's capacity. The fuse will just blow quicker and that's not a bad thing.