Need advice on a reliable 36v solar setup, our current setup is hopeless

[jmh59]

I work on a heritage railway and we need to run a ~30v point machine on occasion. This takes around 7 amps for up to 10 seconds (maybe 10 amp starting) and is used maybe 8 times a day, a few days a year often with months in between uses.

Currently there is one panel that produces around 42v off load, a Renogy boost charger, 3x 110Ah lead acid batteries, and a 48-24v converter between the panel and Renogy as the panel generates too high a voltage in the sun for the Renogy which gives up. If the panel voltage drops too low the converter cannot maintain its 24v output, the Renogy will not accept the solar input, the batteries drain and then the Renogy refuses to even try to charge them.

So I want to start again and get it right.

We have used Victron products before and there is one, a Bluesolar MPPT 150/35 which has to be set to 36v by software and can apparently cope with flat(-ish) batteries (though I cannot now find that stated in their documentation). I also like the cellular reporting add-on they have. But I am sure there are other products.

Has anyone used or knows of a solar charger that will actually cope with batteries as they drop (maybe they all do, this is new to me). The last time we were there one battery had dropped to 6v, we have had them flatter and they will actually take a charge back at base but getting them back to base is a struggle. Any advice welcome!

 

[DIYrich]

Typically, the Victron will need 5 volts over the charge voltage of the battery. It will take up to 145v.
You should have some type of cutoff so you don't overdrain your battery.

 

[jmh59]

Typically, the Victron will need 5 volts over the charge voltage of the battery. It will take up to 145v.
You should have some type of cutoff so you don't overdrain your battery.

Noted thanks that's very useful info - I was told +20v by a vendor but the vendor is no longer replying to my emails! Shame really as I was about to buy the kit from them. The batteries will not be over drained - during use the motor simply will not engage if the voltage (or more probably the current) is too low and someone would (hopefully!) report that to us. They are presumably simply self discharging over the months they are not used.

 

[DIYrich]

They are presumably simply self discharging over the months they are not used.

Lead Acid batteries like to be stored fully charged. You should not let them self discharge.

 

[rogerheflin]

I work on a heritage railway and we need to run a ~30v point machine on occasion. This takes around 7 amps for up to 10 seconds (maybe 10 amp starting) and is used maybe 8 times a day, a few days a year often with months in between uses.

Currently there is one panel that produces around 42v off load, a Renogy boost charger, 3x 110Ah lead acid batteries, and a 48-24v converter between the panel and Renogy as the panel generates too high a voltage in the sun for the Renogy which gives up. If the panel voltage drops too low the converter cannot maintain its 24v output, the Renogy will not accept the solar input, the batteries drain and then the Renogy refuses to even try to charge them.

So I want to start again and get it right.

We have used Victron products before and there is one, a Bluesolar MPPT 150/35 which has to be set to 36v by software and can apparently cope with flat(-ish) batteries (though I cannot now find that stated in their documentation). I also like the cellular reporting add-on they have. But I am sure there are other products.

Has anyone used or knows of a solar charger that will actually cope with batteries as they drop (maybe they all do, this is new to me). The last time we were there one battery had dropped to 6v, we have had them flatter and they will actually take a charge back at base but getting them back to base is a struggle. Any advice welcome!

How old and what type are those lead acid cells? One dropping to 6v indicates at least a few dead cells and/or a dead batteries or possibly a battery needing to have some water added. If it did not get charged for too long and discharged it is likely dead.

 

[jmh59]

Lead Acid batteries like to be stored fully charged. You should not let them self discharge.

Thus the solar charger... when it works.

 

[time2roll]

I assume the sun is unreliable and the solar does not keep up with self discharge + intermittent load.
Need an actual solar charge controller where the battery voltage can be correctly set for the battery. Charge controller will wake up immediately with minimal sun and charge the battery to full voltage given enough sun. Add more panels if needed.

If the point machine needs very close to 30 volts DC consider building a LFP battery with individual cells. Need 10 cells to get 32 volts and run direct from the battery. A good solar controller can be set to the proper charge voltage (about 34 volts). May need a small heater if the battery will be exposed below 4C. This system should run 20 years with virtually zero maintenance.

 

[jmh59]

How old and what type are those lead acid cells? One dropping to 6v indicates at least a few dead cells and/or a dead batteries or possibly a battery needing to have some water added. If it did not get charged for too long and discharged it is likely dead.

They are Shield 'powerstation dual use' 110Ah ones but we never get them new - they have probably seen a lot of service underneath a carriage before we got them. I need to see if anyone checked the water level but we've had these well down before and they seem to recover and hold charge - not how I remember from my early driving days, dead stays dead.

 

[jmh59]

I assume the sun is unreliable and the solar does not keep up with self discharge + intermittent load.
Need an actual solar charge controller where the battery voltage can be correctly set for the battery. Charge controller will wake up immediately with minimal sun and charge the battery to full voltage given enough sun. Add more panels if needed.

If the point machine needs very close to 30 volts DC consider building a LFP battery with individual cells. Need 10 cells to get 32 volts and run direct from the battery. A good solar controller can be set to the proper charge voltage (about 34 volts). May need a small heater if the battery will be exposed below 4C. This system should run 20 years with virtually zero maintenance.

I thought those types of battery did not like to remain fully charged for a long time? We might be talking 4 or 5 months of non-use.

Yes it seems a perfect storm, overcast = low solar output, drops below what the converter can cope with, the Renogy gives in, and maybe one battery is a bit duff anyway.

The motor is happy at 36v.

The big question is will the Victron MPPT 150/35 (plus the cellular monitor I want) actually work for us - it seems to be ideal but when I ask vendors they just say yes it will work without giving me any tech talk, but I do apparently need them to set the thing to do 36v as Victron says it needs software to tell it. My plan (so far) is to get that solar charger and cellular gubbins, possibly / probably a higher voltage panel, and three actually new batteries, not the hand downs we get. But I tend to doubt stuff until I see it actually work.

Thanks for the advice / info so far!

 

[time2roll]

I thought those types of battery did not like to remain fully charged for a long time? We might be talking 4 or 5 months of non-use.

Yes it seems a perfect storm, overcast = low solar output, drops below what the converter can cope with, the Renogy gives in, and maybe one battery is a bit duff anyway.

The motor is happy at 36v.

The big question is will the Victron MPPT 150/35 (plus the cellular monitor I want) actually work for us - it seems to be ideal but when I ask vendors they just say yes it will work without giving me any tech talk, but I do apparently need them to set the thing to do 36v as Victron says it needs software to tell it. My plan (so far) is to get that solar charger and cellular gubbins, possibly / probably a higher voltage panel, and three actually new batteries, not the hand downs we get. But I tend to doubt stuff until I see it actually work.

Thanks for the advice / info so far!

The LFP are fine sitting at full charge when charged by solar. It is the continuous charging at max full voltage plugged into the wall 24/7 that will shorten the life. Perfectly fine to charge LFP at less than the max voltage for light duty use. And unlike lead-acid they can sit at 20% to 50% indefinitely if there is limited sun. Lead-acid will sulfate and lose capacity. Will need a couple balancers between three 12v batteries in series.

My RV is only used about 4x per year but has solar on top and is always charged and ready to go. No issues or maintenance five years running. Quick check is easy with a blue-tooth phone app.

 

[DIYrich]

I thought those types of battery did not like to remain fully charged for a long time? We might be talking 4 or 5 months of non-use.

Discharge LiFePO4 to 80%, and disconnect. It will be fine for 4-5 months.

 

[jmh59]

Discharge LiFePO4 to 80%, and disconnect. It will be fine for 4-5 months.

Can't disconnect anything as we never know exactly when it is needed.

 

[SomethingAppropriate]

ahh another terrible experience with Renogy.

Its like as sure as the sun setting each night.

 

[rogerheflin]

Can't disconnect anything as we never know exactly when it is needed.

The only disadvantage of LiFePO4 is that it cannot be charged below 4C (or so) so if the location has long periods of that then some sort of Lead Acid is better.