Do you really need a $400 charger?

[Dockhead]

Originally Posted by kmacdonald

As the battery acceptance decreases the charge current will decrease thus decreasing any voltage drop in the wiring. This doesn't mean you don't need to properly size the wiring but it does mean voltage drop isn't as harmful as some people would lead you to believe unless of course you are PSOC cycling your batteries, then charge time to say 85% SOC would be increased.

You are right about voltage drop and current -- an interesting point. But you need to hold the voltage at a certain value during the whole absorption phase, in order to convert the last part of the lead sulfate back into lead and sulfuric acid. This is a key point in lead battery operation.

[kmacdonald]

Originally Posted by Dockhead

Are you sure about that? Both my Victron and the previous charger, a Newmar, originally installed when my boat was built, have/had separate wires for voltage sensing.


I see from this that Sterling has a separate voltage sense wire:


https://cdn.shopify.com/s/files/1/06...22295855460459


If you can adjust the charging voltages, you can deal with this that way, by measuring yourself and then setting the voltages to account for the drop. But I thought all quality battery chargers had separate voltage sense wires.

Adjusting the charge voltage won't compensate fully for voltage drop in the wiring. The voltage drop varies with current so adjusting the output voltage only works for one specific value of current. Separate voltage sense solves that problem.

[Dockhead]

Originally Posted by kmacdonald

Adjusting the charge voltage won't compensate fully for voltage drop in the wiring. The voltage drop varies with current so adjusting the output voltage only works for one specific value of current. Separate voltage sense solves that problem.

This is all true.


But you can compensate approximately by turning up the absorption voltage. Remember the charger will drop to float at some point. Somewhat higher absorption voltage at the end as current tapers off is usually not a big deal; but not maintaining a minimum absorption voltage really is a big deal -- sulfation.

[CGirvan]

Originally Posted by a64pilot

Just for whatever it’s worth, three stage chargers are really only two stage.
Balmar 614 alternator controller being an odd ball.
But what happens is that you have two voltage set points. Absorption and float.
Bulk is the charger trying to achieve absorption voltage, but can’t cause its current limited, it is not a separate “stage”.
Once absorption voltage is reached, usually a timer is started and that voltage held until the timer end, where the voltage is set to float.

I can see the advantages of a 2/3 stage charger for lead, but have been thinking that for LiPo you really just need bulk so have thought about using a benchtop power supply. This obviously couldn't be left and would need to be monitored.



I'm rarely on shore power so it would only be used for the occasional charge from the Honda 2000. The other advantage a power supply would have is in the initial balancing of the bank.

[travellerw]

Originally Posted by CGirvan

I can see the advantages of a 2/3 stage charger for lead, but have been thinking that for LiPo you really just need bulk so have thought about using a benchtop power supply. This obviously couldn't be left and would need to be monitored.



I'm rarely on shore power so it would only be used for the occasional charge from the Honda 2000. The other advantage a power supply would have is in the initial balancing of the bank.

Look at the IOTA charger I mentioned earlier. Without the IQ4 option, its just a VERY robust power supply. Its designed to run full bore for days on end. It has a pot inside that allows you to adjust the voltage (between 12V and 15V). For LiFePO4 you set it to 13.8V and watch the current. Manually stop when you see C/100.

[john61ct]

Yes a power supply and DMM is fine for LFP, long as you are there to Stop charging when voltage hits your target.

Or a voltage sense trips a switch.

No need for any Absorb in daily cycling, only when precise calibration is required.

For Sterling, see their optional Battery Chemistry Module

[kmacdonald]

Originally Posted by travellerw

Look at the IOTA charger I mentioned earlier. Without the IQ4 option, its just a VERY robust power supply. Its designed to run full bore for days on end. It has a pot inside that allows you to adjust the voltage (between 12V and 15V). For LiFePO4 you set it to 13.8V and watch the current. Manually stop when you see C/100.

I wish someone would offer that in a charger and voltage regulator. It would make LiFePO4 an easy choice.

[travellerw]

Originally Posted by kmacdonald

I wish someone would offer that in a charger and voltage regulator. It would make LiFePO4 an easy choice.

Its interesting you say that.. I'm sure it would be pretty easy to build a small board with a PIC micro (or any micro) to do this on the IOTA charger. On top of that you could also do voltage sense at the battery terminals to ensure a true 13.8V and C/100 current..

Hmm, we will see, it might be my next project! (HEY IOTA, THE FUTURE IS CALLING).

[john61ct]

Sorry which part do you think is not available?

Half the battle is deciding what you really want.

User custom Absorb setpoint?

No Absorb or minimum Absorb time?

Stop charge, no Float? Or user-adjustable Float voltage?

Go to Float (or stop) based on endAmps?

And do you mean alt VR, or solar or mains chargers?

I'm not saying all are cheaply or easily available, but then I keep getting blowback saying the ideal recommendations are not needed anyway.

First decide what aspects of the charge profile are most important to you, and then research among the potential candidates, what you may need to compromise on.

And then don't complain about pricing, obviously all the ancillary infrastructure is going to cost as much or more than the bank.

Just as all the upfitting of a boat may cost more than the boat did bare.

[kmacdonald]

Originally Posted by travellerw

Its interesting you say that.. I'm sure it would be pretty easy to build a small board with a PIC micro (or any micro) to do this on the IOTA charger. On top of that you could also do voltage sense at the battery terminals to ensure a true 13.8V and C/100 current..

Hmm, we will see, it might be my next project! (HEY IOTA, THE FUTURE IS CALLING).

It would require a shunt to sense current in a charge bus since multiple charge sources could be used simultaneously. Each of the charge sources would need the same ability to stop charging at C/100 Amps total or be controlled by one "smart device". I bet no one wants to support such an installation in such a diverse field.

[john61ct]

Started a new thread for the above

http://www.cruisersforum.com/forums/...fp-208351.html

[travellerw]

Originally Posted by kmacdonald

It would require a shunt to sense current in a charge bus since multiple charge sources could be used simultaneously. Each of the charge sources would need the same ability to stop charging at C/100 Amps total or be controlled by one "smart device". I bet no one wants to support such an installation in such a diverse field.

No, you are overthinking it.. However, there are BMSs on the market that do exactly what you describe and then control the charge sources.

I'm willing to bet the IOTA has a shunt in it and that data is available on the IQ4 port. You don't need to know about other charge sources. You just cut charging when you hit your target voltage/current. Of course other charge sources would mean you cut early, but that is not an issue. You just rely on them to finish charge.

The hard thing to detect is the loads. The shunt might see 15A of current going out, but 10A of that could be load (fridges, freezer, lights, ect). In that case you may never get to the target current. The common approach to this issue is to just watch for a large change in current. Once that is seen, then charging is held for X more minutes, then cut. Again, we error on the safe side and cut possibly early. The downside to this algorithm is that solar chargers can trick it into thinking a cut is required. However, that is less likely with LFP batteries since they will take pretty much everything you can throw at them.

Now with all that said... Its probably MUCH easier to just hook the charger up through a timer. I could probably calculate within a few minutes how long my charger needs to run, even with other charge sources.

[kmacdonald]

There are just too many variables and disparity in installations to design a "drop in" foolproof LFP system. They should only be used by technically savvy cruisers who are willing custom design, build, and manually control the system. With all the benefits of LFP, someone would have already have done it if it was possible. A lot have tried and as far as I know they have failed for the most part. There are some installations working well but that's due to the end users knowledge and not a foolproof design. The design considerations exceed the scope of any internet forum discussion.

[travellerw]

Originally Posted by kmacdonald

There are just too many variables and disparity in installations to design a "drop in" foolproof LFP system. They should only be used by technically savvy cruisers who are willing custom design, build, and manually control the system. With all the benefits of LFP, someone would have already have done it if it was possible. A lot have tried and as far as I know they have failed for the most part. There are some installations working well but that's due to the end users knowledge and not a foolproof design. The design considerations exceed the scope of any internet forum discussion.

Hhhmm have you looked into Lithionics or Victron LFP?

I have seen at least 1 install of each where the "end users" definately contributed ZERO to the installation and operation. Both systems had been in operation for over a year (one sytem over 2 years). The owners had no clue how any of it worked and just let the system take care of itself.

So it is possible, however the price was quite astounding.

[john61ct]

Yes, as long as the noob is trainable, willing to pay attention.

And write big checks.

DIY is easy if you watch everything yourself.

Trying to get foolproof automation becomes a science project.