12v x12 battery pack 12v solar controller

[Kburg55]

Hi, I recently replaced my battery pack for my propulsion. I am searching for ideas on a relay to charge my pack individually.



My solar controller will go to a secondary battery when the primary is full. I am searching for what I assume to be a voltage sensing relay that can cycle through the battery pack. 12 channels I'd imagine.


I understand that it will take a long time to fully charge and will unbalance the battery pack if it doesn't cycle fully. Just looking for a way to top up the batteries while away.



Thanks for your insight,



Kevin

[john61ct]

Please give a bit more big-picture clarity about your setup.

Why not just bulk charge at the desired full-bank voltage?

Why do you want to get the bank "topped up" while it's not being cycled?

What is your usual energy source, how long do you stay away from shore power?

Are you **only** charging this propulsion bank? What is its composition, chemistry, bulk charging vs nominal voltage, how many total packs, xPyS layout at the top level in "packs", and then the same with the cells within each pack?

Does each pack get its own BMS? Is there a master controller over all?

If other banks need charging, what types, what voltage(s)?

[Kburg55]

Thanks for your response!

My current set up is 12, 12V100Ah lead acid agm batteries.

My bulk set up is 144v 30a charger, which I run off shore power or from a 2000W Honda generator.

Sadly I cannot leave it plugged in as it is the refueling dock that has power...

Also the shore power is underrated and I can only charge at about 6 amps in at 144v. With the generator I am getting around 11 amps at 144v.

So my new strategy is to upgrade my solar to around 150 watts which should be enough to get me 10 amps at 12v.

Hopefully I can find or configure a voltage sensing relay that at 15v or full charge, could digitally select the output to the next battery in the series.

Let me know if I am dreaming here or if something like this exists

I do not have a BMS. The charger is a 3 stage adjustable voltage and amperage. I can monitor the individual batteries from a tree of banana plugs to a multimeter.

1-12 each connection for on the positive terminal of the next battery with a ground on 12 as well.

My hope would be to use that "tree" as a relay for a 12v solar charger.

Regards,

Kevin

[john61ct]

Well to start, 12x 12V in series should be charged at between 168V and maybe 178V, depends on the specific model batt.

@144V 6A is 8-900W, so not so bad, but yes at earlier stages they will accept the genset output faster, try to get the bank up to 85-90% before the solar day starts, let panels handle the remaining 5+ hours needed to get to Full, if they can.

10 amps at 12v through each batt will not be even close to enough, be like filling a bathtub with a spoon, the rotating idea is just putting buckets in between.

You really need a bigger power source, and just use solar for topping up, upconverting the SC output to the target bulk voltage.

If you want to go with a lower voltage increment, say 2x 87.5V to get to 175V, the two converters will be series-connected at the midpoint center tap.

If you want to do 3x chargers, you're now at a pretty standard 48V nominal, check out Genasun's SCs.

But again you really need like 24 panels not 2.

Once you get the power source sorted, bringing in an electrickery guy from the EV or eBike world will be a good idea, check out Endless Sphere for leads.

Note if you went to LFP, at least most of the genset output gets into the bank the whole cycle, instead of just up to 85%

[meridian28]

I’m confused. Are we talking 14.4v or 144v?

[john61ct]

144V for 12V x 12S (12 in series), but as stated that's just nominal.

If that batt wants 14.4V setpoint the 173V is called for charging the whole bank from one charger.

It is a propulsion bank, not House.

[Kburg55]

Originally Posted by meridian28

I’m confused. Are we talking 14.4v or 144v?

144v



So in my system charging voltage is actually 168v at around 6 amps from shore power. I can go from 50% depth of discharge and nearly fully charge up in 10 hours. But I am limited in my time at the boat and dock as I live away.



I'm looking for a solution to cycle through my battery pack and charge each 12v cell with a singular solar controller.



As per drop in the bucket, I'm normally away from the boat for 2 weeks at a time so I assume enough daylight hours to charge 12 12v batteries from 50% DOD on 150w.


50% DOD = 50ah



15v @10a for 5 hours

= full batterty


Cycle to next x11



I was considering the possibility of 12 panels @12v in series to achieve 144 volts but it seemed unnecessary for my casual use.



Am I nieve to charging rates for solar?



Thanks again,



Kevin

[john61ct]

In ideal insolation conditions 150W of panel will feed a hungry bank ~700Wh per day: 50Ah @12V but only ~4Ah per day at 168V.

With that, you can work out the "enough power" issue.

> I'm looking for a solution to cycle through my battery pack and charge each 12v cell with a singular solar controller.

Even **if** you could find (or build) such a "round-robin charging multiplexer" - I'm saying that is a fundamentally flawed concept, will be a waste of time and money. Even dangerous, if it works for a while, still likely too unreliable to leave unattended, may well damage the bank or your other gear.

DC-DC conversion charging the **whole bank at once**, several different options as outlined above, is the way to go.

> I can go from 50% depth of discharge and nearly fully charge up in 10 hours.

Maybe in theory, unlikely in practice, unless you call 85% "nearly Full"

Remember, the last 15% takes 4-5 times more hours than it does to get from depleted to 85%, no matter how much power is available.

And the higher percentage of lifetime the bank is lower than Full the faster it will need replacing. "Nearly Full" does not help prevent this, only 100% true Full as defined by endAmps according to your battery datasheet.

And that is assuming a high quality lead battery model truly designed for deep cycling.


> I was considering the possibility of 12 panels @12v in series to achieve 144 volts but it seemed unnecessary for my casual use.

You do not need a lot of panels to get high voltage.

You need them to get a lot of amps at high voltage.

[Kburg55]

I guess I will have scheme on how to afford some new panels and controller. I appreciate the help.



I will do some looking into dc-dc chargers, and into high voltage solar. What amperage do you think necessary to top up to 100% @168v?

As per your previous reply what does LFP refer to? I am not familiar.
Thanks for your patience,
Kevin

[john61ct]

Originally Posted by Kburg55

What amperage do you think necessary to top up to 100% @168v?

Need your battery model, ideally a link

LFP = LiFePO4, aka Lithium iron phosphate

If you are on a low budget, don't start down that rabbit hole

[Rapanui]

You could run an inverter from the 12v battery and operate a battery charger for the whole battery array. You would need to manage when the inverter operates to prevent the 12v battery being permanently in PSOC and probably need more solar. It would have side benefits in that it could eliminate that massive battery array being constantly in PSOC and provide quieter charging than the Honda

[john61ct]

Doing triple DC to AC to DC adds no energy, will not help avoid PSOC

only **loses** energy due to greater conversion losses.

And think about it, how will one 12V unit store the energy to fill up a dozen of the same size?

Convert to Wh and do the math, if it isn't just 100% obvious to you intuitively.

The only actual energy sources here are

1. solar (poor)
2. genset (medium)
3. shore (ideal)

[Pete7]

Originally Posted by Kburg55

So my new strategy is to upgrade my solar to around 150 watts which should be enough to get me 10 amps at 12v.

Yes but only in full sun, the middle day hours, during the summer. We have 150w and generally works well, the higher latitude = longer summer days plus cooler temperatures work in your favour too. After a couple of cloudy days or rain we need to do something else which is why we have added 110A folding panel this year. It's light enough to fold away at the side of a berth.

However, it will help maintain the bank whilst you are away and if you could double it to 300w then great, but above that you start to run out of real-estate to put solar on a smaller yacht.

Pete

[Rapanui]

As a physicist I clearly understand that my suggestion will not create additional energy but as a systems engineer I would contend that charging in series is a better approach to treating the 12 batteries better by keeping them at the same state of charge. Clearly the OPs design needs far more solar to do this and also to regularly get all 12 fully charged as often as possible as charging with a Honda will not do that unless run for many, many hours. Clearly 1 12V house battery cannot charge 12 batteries from its storage, either if you do that on the array or battery by battery. It can only charge when there is excess solar and as I said you would need to ensure that the house battery is returned to 100% daily.
A far better system would be to have a separate solar array and charge controller for the 12 battery array if only to safeguard the considerable investment by the OP from death by sulphation.

[Kburg55]

Here is a link with the battery specs. I did most of my research but went with the lowest cost option.



https://drive.google.com/file/d/0Bxl...w?usp=drivesdk


My charger on shore power gets a voltage runaway effect after full charge. It hits 192v at less than 1 amp. Not the greatest for leaving it on as a tender. But built in timer at 3rd phase... So not bad. But I wish I could control it a little more.


The batteries recommend constant voltage charge which is the 2nd stage charge at 172.8v

Ideally I could buy a new charge controller that has solar as well as ac input and is constant voltage output

180v max charge voltage @15v x 12

20amp max charge input

I will try and find a buck/boost dc-dc converter.

3.6kw peak?

Is it possible to use a dc-dc in the same circuit as the ac-dc charger. As a voltage regulator?