AGM min max voltage and charging

[Russ]

I cannot find the thread when I asked about minimum charge rate on a Vmax 125 ah. The sticker on the battery says 14.7 recommended 14.5 v maximum charge. What should I set the PWM and the ATS at for minimum charge?
Right now it has been cloudy for a few days and some rain. I am using a older Craftsman charger set to 2 amp charge and marine battery type. When the charger said charged I think it only said about 13.7 or .8. Any idea why it will not hit 14.7 or 14.5?

 

[gnubie]

Probably simply because it's a basic charger.

Charging a lead acid battery at 13.8 will work but due to the nature of the battery it will take quite a while to get to fully charged because the current tapers off fairly early in the charge cycle. Absorption charging needs more circuitry to detect the initial drop in current during charging, kick up to absorption stage voltage and to monitor the current drop there to determine end of charge and to go back down to float voltage. That can all be done with discrete components, even combined into a single chip charger solution, but a lot of the time these days it's done with a microcontroller.

For the other question, I think you are asking at what voltages things should be turned off and on. That's a question that you need to consider if there is any load on the battery and how much of a load. There's a lot of scope for discussion on that topic but depending on how hard you want to treat the lead acid battery you might want to set the controller to disconnect it's load output terminals at 11.3 volts and to reconnect at 12.5v. I'm sure other people will come up with other voltages, and why.

 

[Russ]

Man I did not understand the first paragraph.
Are you describing the the battery charger and it microcontroller ?
What is monitoring the charge the charger or the PWM?
What charger would you recommend any idea?

Do Lithium batteries charge faster? I could get a Valence

I apologize for the questions but I have not thought that deep into a charger

 

[gnubie]

Are you describing the the battery charger and it microcontroller ?

Yes, describing what a smart battery controller does compared to a dumb controller, as a possible explanation of why your charger only does 13.8v charging.

What is monitoring the charge the charger or the PWM?

Probably not a good idea to have both supplying current at the same time, but if both were connected at the same time they would both be paying attention to the state of charge of the battery.

*more confusing technical stuff*
If you did connect and power on both the charger would lift the battery to 13.8v and the PWM controller would probably be happy with it doing that, then the PWM controller would sense that it wasn't providing much current to the battery and change to its absorption charging mode and pull the voltage up higher. That would cause the current from the dumb controller to fall significantly, not that it would care, and the PWM controller to take up the slack, again not a problem. After the PWM controller is happy that the battery is fully charged it would go back down to 13.8v for float charging and then the charger and the PWM controller would share the load.

What charger would you recommend any idea?

There's a million and one smart lead acid chargers out there. I'm in 240v land and I think you are in 110v land, so any charger I'm familiar with won't be any good for you. Maybe someone else can give you advice there, but there's a wide selection on ebay and amazon.

Do Lithium batteries charge faster?

They charge differently. A lifepo4 doesn't have the early current tail off that a lead acid does so can use a simpler charging strategy but given how cheap smart chargers are these days that's largely not a concern anymore. You can abuse both lifepo4 and lead acid to get very high charge rates and both will suffer some degree of performance degradation as a result.

lifepo4's big advantages are weight vs energy storage, number of charge / discharge cycles, and not needing to be religiously bought up to full charge. Lead acid batteries need to be regularly fully charged and held there when ever possible otherwise they'll have reduced lifespans.

I apologize for the questions but I have not thought that deep into a charger

No need to apologise, asking questions and having them answered is the whole point of this forum.

I'm sure someone will step in and make corrections if I've made any errors.

 

[Russ]

Yes, describing what a smart battery controller does compared to a dumb controller, as a possible explanation of why your charger only does 13.8v charging.


Probably not a good idea to have both supplying current at the same time, but if both were connected at the same time they would both be paying attention to the state of charge of the battery.

*more confusing technical stuff*
If you did connect and power on both the charger would lift the battery to 13.8v and the PWM controller would probably be happy with it doing that, then the PWM controller would sense that it wasn't providing much current to the battery and change to its absorption charging mode and pull the voltage up higher. That would cause the current from the dumb controller to fall significantly, not that it would care, and the PWM controller to take up the slack, again not a problem. After the PWM controller is happy that the battery is fully charged it would go back down to 13.8v for float charging and then the charger and the PWM controller would share the load.


There's a million and one smart lead acid chargers out there. I'm in 240v land and I think you are in 110v land, so any charger I'm familiar with won't be any good for you. Maybe someone else can give you advice there, but there's a wide selection on ebay and amazon.


They charge differently. A lifepo4 doesn't have the early current tail off that a lead acid does so can use a simpler charging strategy but given how cheap smart chargers are these days that's largely not a concern anymore. You can abuse both lifepo4 and lead acid to get very high charge rates and both will suffer some degree of performance degradation as a result.

lifepo4's big advantages are weight vs energy storage, number of charge / discharge cycles, and not needing to be religiously bought up to full charge. Lead acid batteries need to be regularly fully charged and held there when ever possible otherwise they'll have reduced lifespans.


No need to apologise, asking questions and having them answered is the whole point of this forum.

I'm sure someone will step in and make corrections if I've made any errors.

I flip the breaker the battery plugs into but the negative battery cable is still connected.
I don't know what charger to use but maybe they are all smart chargers now.
Can a Lithium battery be charged with most any smart charger?

 

[gnubie]

lifepo4 batteries are often considered to be drop in replacements for lead acid of the same voltage and for the sort of use we have on this forum they are. A run of the mill lead acid charging will also be able to charge the lifepo4. Attention still needs to be paid to ensure the current the charger supplies doesn't exceed the recommending charging rate of the lifepo4. If the battery's recommended charging rate is 30amps the charger should supply that at the maximum. If the battery's BMS sees something it doesn't like such as high voltage it will disconnect to protect the battery but the average BMS is quite happy with you charging the battery at a rate of amps that will shorten the battery's lifespan.

I know there are smart lead acid chargers that deliberately put very spikey voltage across the battery in order to try to desulphate a damaged lead acid battery and to be honest I'm not sure of the consequences of that with a lifepo4 battery. Time for a battery expert to weight in perhaps?

 

[Russ]

Well we can forget this I just bought 2 Valence 138 ah for 800.00 including shipping. Hope that was a good deal seemed about as good as any

 

[gnubie]

That's one way to take care of it