\is there a "Magic Box"?

[JimJohnston]

Hi all,

a "magic box" will do wonderful things. This is why I need one.

In a project to install 2 x 100 W solar panels to charge my 2 x 24V Torqueedo batteries (connected in series for 48V), I would like to connect the two panels in series in order to get maximum voltage to the mppt controller.

Torqueedo requires one controller per battery (unless they are connected in parallel). Batteries may not be charged while in series connection. They can be charged concurrently with the charge controllers in parallel. That's how the 120V chargers work when I use shore power.

One person suggested charging battery 1 first and then disconnect and reconnect to battery 2. Rather than mess with wires and connections or even switches, I think the "magic box", if it exists, could do this connect/reconnect automatically based upon voltage levels or some parameter.

Can anyone suggest a "magic box" or even if such exists?

Thanks for you input.

[john61ct]

There may well be ways to automate the charging of your bank, but figuring out how will require information specific to those particular batteries.

The thread title really should contain such relevant terms in order to perhaps attract members familiar with them, e.g.

"Charging Torqueedo batteries wired in series"

Have you established a good rapport with Torqueedo support to be able to ask the relevant questions?

To start with, ignore the solar aspect, please clarify what you mean wrt your shore power charging.

The word "controller" as you used it is ambiguous, please use "charger" for AC-to-DC, and SC when later referring to a solar controller unit.

Originally Posted by JimJohnston

Batteries may not be charged while in series connection.

Can you get an explanation from them as to why?

> They can be charged concurrently with the charge controllers in parallel. That's how the 120V chargers work when I use shore power.

Do you mean that you physically remove the serial connection every time you charge?

In other words you can't use the bank to feed any loads while also charging, you need to connect / reconnect the bank wiring switching between the two separate modes, multiple times every cycle?

If so, why was the system designed this way, why select those batteries if they are so poorly suited to your use case?

If you could give the battery model# ideally link to the datasheet/manuals maybe that will help.

So long as the charger outputs are electrically isolated from each other and from their inputs, you should be able to use 2x 24V units wired via the midpoint tap while the batteries are still wired in series.

Note I am **not** suggesting this for a DIY project. Once you figure out a solution that works for your use case, I definitely advise getting a professional involved, to at least oversee the implementation.

[JimJohnston]

Hi John

everything made so much sense to me when I wrote it. Funny how that happens.

To be more precise, the batteries are for propulsion. They are the Torqueedo model 26-3500 24V nominal each. They are connected in series to provide 48V to the motor.

The current 120V AC-DC chargers are permanently installed. When batteries require charging and I have shorepower, a master switch turns on the twin chargers. The BMS regulates the charging process. LEDs indicate the level of progress.

I hope to provide some off-grid power by way of solar chargers. Toqueedo sell two chargers designed to work with these batteries. A simple one (https://www.torqeedo.com/us/en-us/pr...4/2207-00.html) which costs $499
An expensive one (https://www.torqeedo.com/us/en-us/pr...-/2211-00.html) costs $1299.

Both solar chargers can be connected to the batteries (as you pointed out) if their outputs are electrically isolated.

It is the input side that I understand where the two SC's cannot be isolated from each other. Hence the idea of a magic box to make use of the higher priced charger to alternate between the two batteries.

I think I am looking for the solar charger system to essentially mirror the AC charger system where there is only one 120V input. I.e. two SC's to 2 batteries and one input from the panel.

When the batteries were purchased they seemed to be the right choice at the time (and I think they still are)

The manual for the $499 charger is here: http://media.torqeedo.com/downloads/...ger-manual.pdf

The manual for the more expensive solar charger is here:https://media.torqeedo.com/downloads...-104_DE_EN.pdf

I agree entirely that the work is not DIY. Too old and too stiff for that.

Finally I thought that a title with "magic box" in it would attract more interest and hence, response.

[john61ct]

Sorry, but I want to set aside the solar side for now, where there is definitely some confusion on multiple points.

And I'm still not clear on the fundamentals, how you are currently doing your shore power charging.

Again,

> Do you mean that you physically remove the serial connection every time you charge?

IOW are you changing the battery wiring, from series-48V to parallel-24V. every time you charge?

Or using 2x 24V chargers in series, +/- joined at the midpoint tap while the two batteries are left in series at 48V?

Or something else?

______

> Have you established a good rapport with Torqueedo support to be able to ask the relevant questions?

Originally Posted by JimJohnston

Batteries may not be charged while in series connection.

Originally Posted by john61ct

Can you get an explanation from them as to why?

In other words you can't use the bank to feed any loads while also charging, you need to connect / reconnect the bank wiring switching between the two separate modes, multiple times every cycle?

[Dsanduril]

John,

my understanding, the OP has two 120V chargers. The outputs are connected one to each battery even though the batteries are in series. The batteries stay connected in series, and each charger charges one battery of the pair. The BMS(s) are built into the batteries, so they stop the charge, etc. individually when a battery is full. With this setup the OP has a single 120V connection that feeds two chargers, that then go into two batteries.

He's looking for a similar setup for his solar - one feed of xxxV from the solar panel/array into two chargers so that he can charge both batteries at the same time. Alternatively, if I understand correctly, a magic box that would charge one battery from solar, then switch to the other when the first is full, all while the batteries are still in series - this part is just a relay on the SC output, but would require a signal from the BMS to say when the battery is full - or use a voltage sense of some sort to evaluate that condition.

[JimJohnston]

Hi Dsanduril

I think you have captured the essence of what I hope for and described the current situation nicely as it exists.

John, to answer an earlier question, yes I can load the batteries whilst they are receiving a charge.

The on board 120V AC chargers receive power from typically a 30Amp x 120V on shore power supply through the usual breaker panel for that type of power. The AC chargers are hard wired to the panel with GFCI breakers in the two circuits.

When I mentioned disconnecting and reconnecting a solar charger it was at the suggestion of a dealer who tells me that at a trade show that is what he does to use a SC to charge 2 batteries and perhaps it could be adapted to my situation. Fundamentally it could be done, but what a nuisance if there is a black box to do it for me.

I haven't yet spoken with torqueedo as I believe there is a wealth of knowledge in these fora where I can elicit help for subsequent discussions with that company.

Thanks so much

[john61ct]

OK then as you mentioned, just replicate the chargers' configuration with the solar controllers.

You should not try to power both SCs from a single panel.

Use at least two, one per SC, and as noted ensure they are each electrically isolated from each other. Of course being fed by separate inputs, that part is taken care of.

Do not be too unrealistic in your expectations about the energy collected per day compared to that consumed by propulsion.

Ballpark in ideal insolation conditions, 4-5kWh per 1kW of panels is about the best you'll average with fixed panels.

About how many square meters of flat space has your boat got available?

Is it a sailboat?

Do you plan on getting away from shore power many days at a time?

Have you got a genset onboard?

[john61ct]

Originally Posted by JimJohnston

Batteries may not be charged while in series connection.

Note this is not true, since you are doing exactly that with your shore chargers.

Just that the chargers, being electrically isolated, are able to connect in series at the same taps where the 24V batteries do to create a 48V bank.

_____
For others reading in future, another way to go, not specific to proprietary Torqueedo gear, would be to have the cells wired in a 48V bank, and to use 48V charge sources.

As usual the BMS should monitor cell-level voltages with the ability to stop the charge cycle to prevent overcharging, even if it does not routinely control the charge source regulation directly.

[guyrj33]

Originally Posted by john61ct

Note this is not true, since you are doing exactly that with your shore chargers.

Just that the chargers, being electrically isolated, are able to connect in series at the same taps where the 24V batteries do to create a 48V bank.

_____
For others reading in future, another way to go, not specific to proprietary Torqueedo gear, would be to have the cells wired in a 48V bank, and to use 48V charge sources.

As usual the BMS should monitor cell-level voltages with the ability to stop the charge cycle to prevent overcharging, even if it does not routinely control the charge source regulation directly.

I think the issue involves two 24v batteries with onboard BMS connected in series being charged by a 48v charger. Once one of the Battery Management Systems shuts down because it's battery is full the other battery connected in series will not be fully charged. Over time this could result in chronic undercharging of one of the batteries.

[JimJohnston]

Originally Posted by john61ct

Note this is not true, since you are doing exactly that with your shore chargers.

Just that the chargers, being electrically isolated, are able to connect in series at the same taps where the 24V batteries do to create a 48V bank.

The Torqueedo operations manual advises:

"4.5.2 Charging mode with batteries connected in series
With batteries connected in series, each battery must be charged with its own charger."

They don't say "why" but I suspect that it is to prevent conflicts in the BMS

[john61ct]

Originally Posted by JimJohnston

The Torqueedo operations manual advises:
"4.5.2 Charging mode with batteries connected in series

With batteries connected in series, each battery must be charged with its own charger."

Yes that is what you're doing, correctly.

But that is being done while the batteries are also connected in series. Which as I said, is also fine, long as the charge sources are isolated.

Originally Posted by JimJohnston

They don't say "why" but I suspect that it is to prevent conflicts in the BMS

Yes, the internal BMSs are not designed to handle the higher 48V voltage.

[john61ct]

Originally Posted by guyrj33

I think the issue involves two 24v batteries with onboard BMS connected in series being charged by a 48v charger.

Yes

> Once one of the Battery Management Systems shuts down because it's battery is full the other battery connected in series will not be fully charged. Over time this could result in chronic undercharging of one of the batteries.

Not at all, the two would would be charged evenly, but yes the BMSs are the issue.

All this would be moot just using a 48V pack.

But as stated the solution is NBD either.

[guyrj33]

Originally Posted by john61ct

Yes

> Once one of the Battery Management Systems shuts down because it's battery is full the other battery connected in series will not be fully charged. Over time this could result in chronic undercharging of one of the batteries.

Not at all, the two would would be charged evenly, but yes the BMSs are the issue.

All this would be moot just using a 48V pack.

But as stated the solution is NBD either.

One battery will have more capacity than the other and therefore be undercharged.
Yes both batteries will have the same number of electrons pass through, but due to differing capacities they will NOT be evenly charged.

[smac999]

Originally Posted by guyrj33

I think the issue involves two 24v batteries with onboard BMS connected in series being charged by a 48v charger. Once one of the Battery Management Systems shuts down because it's battery is full the other battery connected in series will not be fully charged. Over time this could result in chronic undercharging of one of the batteries.

If you are draining and charging at 48v they should never be unbalanced. The issue only comes when people start taping loads mid voltage. Which happens.

Any minor imbalance from a 48v solar contoller would be corrected by the shore chargers every time he plugged in.

[john61ct]

BMV-712 can act as a "mono function BMS" detecting imbalance between two halves of a series string.

Custom tune sensitivity, use the relay to alarm or isolate or trigger a 2-node balancer, whatever you like

Pretty close to a magic box afaic