Float charge

[andsarkit]

Through a regulator? Worth taking some care, even a small panel unregulated can push the voltage of a fully charged battery up too far >

I want some of those 12W panels in the video if they can really push nearly 1A into a fully charged 220Ah battery at over 15V. That doesn't seem to agree with my experience as I have a 30W panel into 200Ah of batteries and I have never seen over 13.6V. I would expect a charger set to 15V would push more than 1A into a 220Ah battery so I wonder what is different about his setup or is it just that UK sunshine is weaker.

 

[GHA]

I want some of those 12W panels in the video if they can really push nearly 1A into a fully charged 220Ah battery at over 15V. That doesn't seem to agree with my experience as I have a 30W panel into 200Ah of batteries and I have never seen over 13.6V. I would expect a charger set to 15V would push more than 1A into a 220Ah battery so I wonder what is different about his setup or is it just that UK sunshine is weaker.

Current from the panel in the video is pretty spot on for no shadow and pointing at the sun, tallys up well with observation - max current rule of thimb - divide panel watts by 20 and add about 20%. So 100w panel on a good day will put out about 6A, 12W panel about a fraction over 0.7A. Just what was shown on the clamp meter in the video.
What you might expect and what happens in the real world are often not the same..........

 

[noelex]

Mosty solar controllers will start a new cycle of boost, absorption and float for each solar day, so your controller will not stay in float even though the battery is fully charged.

The default absorption phase can last for a couple of hours which is not ideal for a fully charged battery with no load. So your fully charged battery is likely to be held at around 14.4v for this time. It takes very little current for a fully charged battery to reach this sort of voltage so your small 20w panel is likely to do this on most days.

Ideally the battery should be kept at a much lower storage voltage which is typically around 13.4v for a 12v system.

The better contollers have adjustable set points and while it is difficult to avoid the boost, absorption and float cycle the voltages for boost and absorption can be adjjusted to the float voltage which effectively disables the other stages.

Controllers with adjustable set points are not necessarily expensive and my recommendation would be purchase one, but given the low cost of your single battery this may not be worthwhile.

If you decide to stay with your existing controller it is worth changing the setting to the option that gives the lowest voltage set points. This is normally the “gel” battery option.

 

[pvb]

Mosty solar controllers will start a new cycle of boost, absorption and float for each solar day, so your controller will not stay in float even though the battery is fully charged.

The default absorption phase can last for a couple of hours which is not ideal for a fully charged battery with no load. So your fully charged battery is likely to be held at around 14.4v for this time. It takes very little current for a fully charged battery to reach this sort of voltage so your small 20w panel is likely to do this on most days.

Ideally the battery should be kept at a much lower storage voltage which is typically around 13.4v for a 12v system.

The better contollers have adjustable set points and while it is difficult to avoid the boost, absorption and float cycle the voltages for boost and absorption can be adjjusted to the float voltage which effectively disables the other stages.

Controllers with adjustable set points are not necessarily expensive and my recommendation would be purchase one, but given the low cost of your single battery this may not be worthwhile.

If you decide to stay with your existing controller it is worth changing the setting to the option that gives the lowest voltage set points. This is normally the “gel” battery option.

The OP's Renogy controller will go to float as soon as the charging current drops below 0.2A. With a fully charged small battery not being used for anything, it sounds likely that the controller will be at float most of the time.

 

[duncan99210]

I’m simply reporting my experience over the past 5 years or so..... I have 180 watts worth of panels feeding a MPPT controller into a total of 600 ah worth of batteries. It works fine, so where’s the problem?

 

[GHA]

I’m simply reporting my experience over the past 5 years or so..... I have 180 watts worth of panels feeding a MPPT controller into a total of 600 ah worth of batteries. It works fine, so where’s the problem?

If the mppt has been going into bulk every day then the problem is your batteries are seeing a much higher voltage than they need to for a few hours day in, day out. Without extensive testing you actually have no idea that 'it works fine' compared to just seeing float voltage. Though how much damage is caused seems pretty much unknown and no doubt depends a lot of temperature. I keep my trojans at absorption when cycling to get them back to 100%, but seems pretty certain leaving a fully charged battery on float isn't as damaging as it seeing absorption voltage every day.

 

[noelex]

The OP's Renogy controller will go to float as soon as the charging current drops below 0.2A. With a fully charged small battery not being used for anything, it sounds likely that the controller will be at float most of the time.

If the controller has a tail current cut off feature that is help in reducing the overcharging.

However, the tail current value tends to increase with controller size so with a 20A controller it may be too high to be of any value with such a small panel and battery.

 

[Catalina36]

Isn't it time you went sailing ?

I wondered what was stopping me leaving the berth. I must unplug that thing.

 

[pvb]

If the controller has a tail current cut off feature that is help in reducing the overcharging.

However, the tail current value tends to increase with controller size so with a 20A controller it may be too high to be of any value with such a small panel and battery.

Do you think that <0.2A is too high?

 

[noelex]

Do you think that <0.2A is too high?

Thinking about the problem a higher tail cut off value is better not worse, but it appears the 20A controller uses the same 0.2A value. Ideally the controller would not enter the bulk/absorption cycle on a fully charged battery, but the tail current feature may stop it staying in absorption for a long time, which is a help.

 

[pvb]

Thinking about the problem a higher tail cut off value is better not worse, but it appears the 20A controller uses the same 0.2A value. Ideally the controller would not enter the bulk/absorption cycle on a fully charged battery, but the tail current feature may stop it staying in absorption for a long time, which is a help.

Exactly the point I was making.

 

[GHA]

Thinking about the problem a higher tail cut off value is better not worse, but it appears the 20A controller uses the same 0.2A value. Ideally the controller would not enter the bulk/absorption cycle on a fully charged battery, but the tail current feature may stop it staying in absorption for a long time, which is a help.

Quick google for the renogy manual says it will stay at absorption voltage for 2 hours, no mention of tail current. Can't be many regulators what have a tail current setting? Pretty useless without it knowing what is actually going into the battery anyway.
Manual also says auto equalization every 28 days, another reason to be wary of leaving batteries connected to that regulator unattended for long periods .

 

[pvb]

Quick google for the renogy manual says it will stay at absorption voltage for 2 hours, no mention of tail current. Can't be many regulators what have a tail current setting? Pretty useless without it knowing what is actually going into the battery anyway.
Manual also says auto equalization every 28 days, another reason to be wary of leaving batteries connected to that regulator unattended for long periods .

It also says "If charging current <0.2A, (absorption) stage will end."

 

[Iliade]

I've just found that my house battery bank has been overcharged (low electrolyte.)

It is charged by a 150w solar panel with photonics universe regulator, a wind genny running though a marlec regulator and the engine, currently running a brand new marine alternator regulator though a split diode system (!) to engine, windlass and house banks.

It is running a compressor fridge and I'm sailing almost daily.


So something has got confused...

 

[VicS]

I've just found that my house battery bank has been overcharged (low electrolyte.)

It is charged by a 150w solar panel with photonics universe regulator, a wind genny running though a marlec regulator and the engine, currently running a brand new marine alternator regulator though a split diode system (!) to engine, windlass and house banks.

It is running a compressor fridge and I'm sailing almost daily.


So something has got confused...

The P'universe controller and the Marlec controller should prevent overcharging from solar and wind but neither may be multistage devices reducing to a float output ( I suppose I should look up the specs for the Marlec controller)
Most likely culprit is your alternator if you are motoring a lot

But you'd expect the diode splitter to limit that by virtue of the volts drop it puts on the alternator output.
Perhaps the regulator is battery sensed and blasting away at full whack into batteries already well charged by the wind and solar

Need some measurements of whats going on. Battery volts and the current from each source.

 

[Iliade]

Need some measurements of whats going on. Battery volts and the current from each source.

Yes thx, I think a new ammeter or two is very high on my shopping list. (I keep blowing the ammeter stages of my multimeters because I'm hopelessly forgetful at changing the lead positions!)