Can I pull the fuse between the controller and panel?

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poot_traveller

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I've got a 160 watt panel and a MPPT controller.  Between the two there is a fuse.  Because the solar panel system generates way more power than I can use per day, I would like to deplete it rather than have it hovering at around 98%-100% like it currently does. 

Apparently having a LiFePo4 battery sitting at 100% long term isn't good for it.  So I'd like to deplete it down to 30%-40% before recharging again. 

Is it safe to pull the fuse?  The panel wires say "don't disconnect under load".  I'm not sure what "under load" means, I think it means don't disconnect while using the power.

Anyway, can I pull the fuse?
 
Since your goal is to maximize battery life I think you would be better off looking for a way change the voltage or state of charge your MPPT controller charges the batteries up to. You may be able to set this in configuration options on the controller. I'd read through the manual or reach out to the manufacturer to find out how to do this.

The method you propose would increase the depth of discharge which has a negative effect on battery life. And you will still be charging to 100% so the batteries will experience the stress of full charge, though it's a bit better than sitting at 100% all the time. So overall I think this would have either no improvement or a negative impact on battery life.

And most fuses / fuse holders are not designed to be disconnected on a regular basis so you may wear them out.

Regarding the safety of pulling the fuse... you could get a spark when you pull the fuse under load. Very unlikely to hurt you but it will degrade the fuse / fuseholder by making burn/score marks on the contact points.

Any device that uses electricity is considered a load so turn off everything before pulling the fuse if you decide to do it. That will eliminate the risk of creating a spark when you disconnect the fuse.

Patrick
 
Wait until night time to pull the fuse, there will be no load at night as the panel is not outputting anything. Taking the battery to 80% sounds better to me.
 
^^^Or just cover the panel or turn it over if mobile.
 
picopat said:
Since your goal is to maximize battery life I think you would be better off looking for a way change the voltage or state of charge your MPPT controller charges the batteries up to. You may be able to set this in configuration options on the controller. I'd read through the manual or reach out to the manufacturer to find out how to do this.

The method you propose would increase the depth of discharge which has a negative effect on battery life. And you will still be charging to 100% so the batteries will experience the stress of full charge, though it's a bit better than sitting at 100% all the time. So overall I think this would have either no improvement or a negative impact on battery life.

And most fuses / fuse holders are not designed to be disconnected on a regular basis so you may wear them out.

Regarding the safety of pulling the fuse... you could get a spark when you pull the fuse under load. Very unlikely to hurt you but it will degrade the fuse / fuseholder by making burn/score marks on the contact points.

Any device that uses electricity is considered a load so turn off everything before pulling the fuse if you decide to do it. That will eliminate the risk of creating a spark when you disconnect the fuse.

Patrick

I'll take a look through the manual to see what it says. I've already ready it multiple time and I don't recall it saying anything, but I might as well double check. Thanks
 
B and C said:
Wait until night time to pull the fuse, there will be no load at night as the panel is not outputting anything. Taking the battery to 80% sounds better to me.

The battery manual says it can be discharged down to 20% or 30% (I can't remember which one) with no problems. That will take me 2 weeks at my current power usage rate.

Pulling the fuse at night sounds like the best option at this point. Thanks for the advice.
 
bullfrog said:
^^^Or just cover the panel or turn it over if mobile.

Covering the panel can create quite a task. When it comes to taking the cover off the panel, the tape that holds the cover on sticks to the panel good and requires a lot of time and effort to scrape the tape and it's sticky substance off.
 
yes, physically pulling the fuse is an acceptable way to disconnect the panel. best practice is to reduce current and voltage as much as possible through fuse before pulling.

the issue is that as you make or break a dc connection the dc current does not like to be interrupted and will arc. the contacts inside MC4 connectors are rather thin and precise in their shape and fit. it does not take much current to melt and disfigure the contacts. i have seen an MC4 contact ruined with just one connect/disconnect while under full power from panel. (one reason i acquired the tools and parts to crimp on my own MC4 connectors ;-) ...)

i always install a fuse in between panel and controller, not just for protection but for the ability to pull the fuse and disconnect the panel when ever i need to. most charge controllers require the solar to be disconnected before disconnecting the battery and the reverse when hooking up the controller. i always try to cover the panels or do that at night so as to not arc the contacts on the fuse but sometimes that is not feasible. the metal contacts of the fuse and holder are much thicker and more durable and can handle several disconnects without causing high resistance. i use the standard automotive blade type fuses and with 10 gauge wire i use the 30 amp size to keep the resistance low and not hurt the voltage drop numbers. these are dirt cheap, can be found almost anywhere and i make my own fuse holders. the fuse and holder can be put together with marine grade components on 10 awg wire (right on solar pv cable) for under a buck $ US. i leave a few inches of wire so if i ever do scorch the contacts it is easy to replace the home made fuse holder.

if it was the case where i a customer that planned to disconnect often, i would consider installing a 30-40 amp dc rated high quality marine switch that is rated to be used under load. just so i didnt worry it might need replacing.

i would NOT use, or recommend using the reset-able circuit breakers people often use as they tend to be relatively high resistance compared to a fuse or high quality switch. they also tend to wear out a little each time they are used to break the current. they may still "work" but the increased resistance can significantly reduce the power actually getting through and would be easy to not notice

i would probably not go to the trouble of disconnecting the solar on a daily basis in an attempt to improve the life span of the lifepo4. but if the battery was used only occasionally, like weekends. then maybe discharging to 60% or so at the end of the weekend and then disconnecting until it was needed might not be wasted effort. when i want to micro manage the charge then i use a fully programmable controller and set the normal charge voltage setting to the volts that equate 80% charge (from manufactures specs) and then set the equalize voltage to be the voltage the manufacturer recommends for a full charge or just a tad under but leave the equalize function turned off in the controller. most of the time, the 80% charge/capacity is way more than enough. but when i know i may need the full capacity i will change the equalize function to on and every day. with my charge controllers this is easy to do as they are bluetooth linked to my cell phone and it takes jst a few seconds to make the switch
 
You can put a battery disconnect switch in between the battery and the controller. These are available online and from marine supply stores too.
Here is one example although they are not showing the controller unit in their diagram. Remember you can try to contact customer support on solar panel companies to ask about setting up a disconnect switch. Be sure you get the exact placement in the system clearly understood in the discussion. No need to pull the fuse when you have a switch installed and it makes the job of disconnecting very simple to do which is of course why these switches exist.
https://mwands.com/shop/product/dc-disconnect-switch-battery-banks-power-sources
 
Gypsy Freedom said:
yes, physically pulling the fuse is an acceptable way to disconnect the panel. best practice is to reduce current and voltage as much as possible through fuse before pulling.

I won't need to manually reduce current and voltage. At night time there will be zero current and voltage coming from the panel and the controller will be in night mode. I'll disconnect at night time when the panel and controller are "sleeping".
 
Gypsy Freedom said:
the issue is that as you make or break a dc connection the dc current does not like to be interrupted and will arc. the contacts inside MC4 connectors are rather thin and precise in their shape and fit. it does not take much current to melt and disfigure the contacts. i have seen an MC4 contact ruined with just one connect/disconnect while under full power from panel. (one reason i acquired the tools and parts to crimp on my own MC4 connectors ;-) ...)

I imagine it would have mess things up good if someone disconnected under full power from the panel. I ain't making that mistake.
 
Gypsy Freedom said:
the metal contacts of the fuse and holder are much thicker and more durable and can handle several disconnects without causing high resistance. i use the standard automotive blade type fuses and with 10 gauge wire i use the 30 amp size to keep the resistance low and not hurt the voltage drop numbers.

So I take it you are disconnecting 30 amp fuses under load and the fuses can take several disconnects before requiring replacement. I think that's what you're saying? If so, it sounds like the only damage getting done is to the 30 amp fuses. This sort of gives me a reference point for what type of damage can be done to the solar panel system as a whole in a worst case scenario when pulling a fuse. Thanks for sharing your experiences.
 
Gypsy Freedom said:
i would probably not go to the trouble of disconnecting the solar on a daily basis in an attempt to improve the life span of the lifepo4. but if the battery was used only occasionally, like weekends. then maybe discharging to 60% or so at the end of the weekend and then disconnecting until it was needed might not be wasted effort.

I won't need to disconnect daily, more like every two weeks at my current power usage rate, even though I use power daily it's not much.

It's just that it never goes below 95% currently.
 
maki2 said:
You can put a battery disconnect switch in between the battery and the controller. These are available online and from marine supply stores too.
Here is one example although they are not showing the controller unit in their diagram. Remember you can try to contact customer support on solar panel companies to ask about setting up a disconnect switch. Be sure you get the exact placement in the system clearly understood in the discussion. No need to pull the fuse when you have a switch installed and it makes the job of disconnecting very simple to do which is of course why these switches exist.
https://mwands.com/shop/product/dc-disconnect-switch-battery-banks-power-sources

If I disconnect the battery, it will trigger over-voltage protection on the controller because the power coming from the panel will have no place to go with the battery disconnected.
 
ya, most controllers do not like being disconnected while there is power coming in. most controller specifically state to disconnect solar input first, and hook up last
 
find a hobby that will use up all that excess energy supply. Or downsize your solar panel array.
 
maki2 said:
find a hobby that will use up all that excess energy supply. Or downsize your solar panel array.

I'll find stuff that will use up the excess energy. I only use a laptop, kindle and mobile currently.

I've only got a 160 watt panel.
 
Just to confirm; pulling the fuse between the controller and panel won't damage the MC4 connectors by any chance, when the sun comes up tomorrow? I mean with the panel receiving charge.

I know those MC4 connectors are fragile and the energy ain't got no where to go with the fuse pulled, so I'm just wondering if that will damage the MC4 connectors?
 
if you disconnect at night you could even disconnect the MC4s and there would be no issue. once disconnected so the circuit is no longer complete there can be no flow of current. the panels are not receiving a charge, they if in the sun will produce max volts but there will be no current flow. as there is no longer a complete circuit. the electrical potential will be there, just like there is electrical potential in a wall outlet in your house even though nothing is plugged in. nothing bad happens
 
Gypsy Freedom said:
if you disconnect at night you could even disconnect the MC4s and there would be no issue. once disconnected so the circuit is no longer complete there can be no flow of current. the panels are not receiving a charge, they if in the sun will produce max volts but there will be no current flow. as there is no longer a complete circuit. the electrical potential will be there, just like there is electrical potential in a wall outlet in your house even though nothing is plugged in. nothing bad happens

Disconnecting the MC4's is a bit harder as these don't come apart easily and could even result in damaging the internal components if done repeatedly.

Popping the fuse out takes less than a second so this option is more desirable.

From what you're saying; popping the fuse will break the circuit and produce no current so can't possibly damage the MC4's. At least that's what I take from it, please correct me if I'm wrong.
 
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