Battery percentage, how low?

[Simon Davey]

So I have this little solar setup at the top of our farm. It runs about 120 watts of light for about an hour per daytime, but also 15 minuets during the evening.

I've added an extra panel because during the previous winter the demand couldn't be constantly met.

 

The extra panel has made a huge difference, and only needs 90 minutes of a decent bright day to keep fully charged.

The last four days have been far too dark and dim though, and it's dropped to 50%.

 

So how low could I let the percentage drop to before I take it off for a mains powered charge?

I've previously only let it get to 60%, but I actually have no idea why.

What do you experts think, could I let it get even lower than 50 %?

 

We like pictures, so here ya go...

 

[Bender]

What battery lead, agm, lithium, some solar chargers can't start charging if it goes below a certain point but I wouldn't be worried about going below 50%, depending on what the battery is.

 

Discharging old style batteries beyond 50% is frowned upon  

 

We used to run our old leisure battery till the pump stopped working or the TV went off, or always charged backup, no idea how much life was taken off with doing that, I was a kid and it wasn't my dept.

 

What voltage is it sitting at at 50%

 

[Simon Davey]

35 minutes ago, Bender said:

What battery lead, agm, lithium, some solar chargers can't start charging if it goes below a certain point but I wouldn't be worried about going below 50%, depending on what the battery is.

 

Discharging old style batteries beyond 50% is frowned upon  

 

We used to run our old leisure battery till the pump stopped working or the TV went off, or always charged backup, no idea how much life was taken off with doing that, I was a kid and it wasn't my dept.

 

What voltage is it sitting at at 50%

 

 

 

It's an AGM leisure battery, no idea of the voltage at 50%. 

I'll have a look tomorrow. 

Thanks @Bender

[Bender]

25 minutes ago, Simon Davey said:

 

 

It's an AGM leisure battery, no idea of the voltage at 50%. 

I'll have a look tomorrow. 

Thanks @Bender

Prob best to charge it it at home while your on  

 

Agm leisure cycle life is usually based on max dod of 50%, you can take them lower but it will shorten it's life slightly, if it's just the odd occasion it's probably irrelevant.

 

Lithium is better for wider discharge rate but more expensive with an increased risk in  

 

Voltage will give you an idea of where it's at.

[Simon Davey]

Nice one, cheers @Bender

[Bender]

The 2 connections on the right of the solar control is the load circuit, if you run from that it will automatically cut supply off at pre set to stop battery from discharging too much

[RideWithStyles]

As a general rule lithium like high rates of charge and loads of “exercise” to work with, so ok to drain them but the only bug if you can’t charge them hard enough they fing hate you and more likely to die. For storage Not to fully charge them- 25-75%.

 

Nic met hrd drys are a little less fussy only they ok with little and often charges, the only thing with them if you store them is to do it fully charged.

[Simon Davey]

39 minutes ago, Bender said:

The 2 connections on the right of the solar control is the load circuit, if you run from that it will automatically cut supply off at pre set to stop battery from discharging too much

 

I never knew that, it didn't have that in the instructions (not that I read them).

I'll look into that, especially as it can be timed, they often turn the lights off, but leave the inverter switched on. 

Thanks again. 

Edited December 13, 2024 by Simon Davey

[Bender]

Usually have a load circuit, can't see very clear from the pic, the idea is the disconnecting the load to save battery getting so low it can't charge it back up.

[Simon Davey]

7 hours ago, Bender said:

Usually have a load circuit, can't see very clear from the pic, the idea is the disconnecting the load to save battery getting so low it can't charge it back up.

 

I thought it was for a small load, I'll try to find out how much current it can supply. 

The instructions have the inverter connected to the battery. 

[Bender]

Should be in the specs, just Google unit

 

If your exceeding that then it's a no.

 

If that's the case a battery shunt and monitor will do the same but at much higher rates, they not that expensive.

[Simon Davey]

Well, I have a max of 240w of LED lighting, now and again that does happen. 

Max load of the charge controller is 30A, so I should be OK. 

The inverter will be supplying 240w which is just over 1amp, not sure what it draws from 12v to make that conversion, but I can't imagine it's anything like 30amp.

[Bender]

Volts x amps or divide as your going the other way etc, 240w is bout 20amp at 12v

[Simon Davey]

2 hours ago, Bender said:

Volts x amps or divide as your going the other way etc, 240w is bout 20amp at 12v

 

The lights work from an inverter, so 230v by 240w gives me 0.96 amps.

However, I don't know how to work out the current draw from the battery that the inverter uses.

Either way, I found the destructions, it says to connect the inverter to the battery, so I can't use the load output 

[Bender]

42 minutes ago, Simon Davey said:

 

The lights work from an inverter, so 230v by 240w gives me 0.96 amps.

However, I don't know how to work out the current draw from the battery that the inverter uses.

Either way, I found the destructions, it says to connect the inverter to the battery, so I can't use the load output 

Roughly 1amp at 12v for every 10w at 240 so 24amp, it's just a case of how efficient your inverter is IE how much it looses in heat and conversion 

[Simon Davey]

9 minutes ago, Bender said:

Roughly 1amp at 12v for every 10w at 240 so 24amp, it's just a case of how efficient your inverter is IE how much it looses in heat and conversion 

 

Brilliant, cheers. 

 

[Bender]

1 minute ago, Simon Davey said:

 

Brilliant, cheers. 

 

Volts amps watts all stay constant it's just what's used that's added to power draw so you can use normal conversion and add a few amps on for inverter

[Simon Davey]

1 hour ago, Bender said:

Volts amps watts all stay constant it's just what's used that's added to power draw so you can use normal conversion and add a few amps on for inverter

 

Excellent, something else I didn't know.

Thanks for your help.

[onesea]

Not really helpful but: 

https://www.sunshinesolar.co.uk/Item/TRIRON3210N?

 

I have solar set up on the boat,  it started with cheap solar controller.   It did the job. 

 

However I upgraded to Victron Smart controller and have not looked back. 

https://www.amazon.co.uk/MPPT-controller-Victron-Energy-75/dp/B075NTT8GH/ref=pd_aw_subss_hxwSS2_sspa_mw_detail_m_sccl_2/262-3055827-1971245?

 

It has Bluetooth and an app, I can monitor loads control voltages it cuts out at see how battery voltage is standing up etc.

You can set your charging voltages,  for me in winter it's set for max battery life.  

When using boat for holiday it set to keep everything running.

 

However I am not certain if that model will cover your set up.

 

Your unit does have a Bluetooth dongle available but what functionality it gives you I don't know. 

 

If you can find the manual and connect the load in to load it output (as @Bender commented earlier connection with light bulb on MPPT).

You can probably set cut out voltage etc. 

 

Another simple addition might just be a voltage meter fixed to batteries. That way you can monitor the voltage.

https://www.ebay.co.uk/itm/356044707704?

You can get without USB but they are same price.

[Simon Davey]

1 hour ago, onesea said:

Not really helpful but: 

https://www.sunshinesolar.co.uk/Item/TRIRON3210N?

 

I have solar set up on the boat,  it started with cheap solar controller.   It did the job. 

 

However I upgraded to Victron Smart controller and have not looked back. 

https://www.amazon.co.uk/MPPT-controller-Victron-Energy-75/dp/B075NTT8GH/ref=pd_aw_subss_hxwSS2_sspa_mw_detail_m_sccl_2/262-3055827-1971245?

 

It has Bluetooth and an app, I can monitor loads control voltages it cuts out at see how battery voltage is standing up etc.

You can set your charging voltages,  for me in winter it's set for max battery life.  

When using boat for holiday it set to keep everything running.

 

However I am not certain if that model will cover your set up.

 

Your unit does have a Bluetooth dongle available but what functionality it gives you I don't know. 

 

If you can find the manual and connect the load in to load it output (as @Bender commented earlier connection with light bulb on MPPT).

You can probably set cut out voltage etc. 

 

Another simple addition might just be a voltage meter fixed to batteries. That way you can monitor the voltage.

https://www.ebay.co.uk/itm/356044707704?

You can get without USB but they are same price.

 

Many thanks, that's some great information. 

I actually bought it all from Sunshine Solar, and the charger is a upgrade because I added an extra panel . 

A volt meter is a good idea, the charger only indicates the charge voltage.