Review/Feedback: LiFePO4 upgrade

[john61ct]

If you're happy to rely on the BMS as the one layer of automated defence against overcharging, and

also to have it be the daily cycling charge control regulator as well, then you're all set.

Just pointing out that is what you have.

It certainly is true that few have more, and if you are keeping an eye on the charging progress maybe that will be fine.

[Stu Jackson]

Originally Posted by aybabtme

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I think my alternator is 80A but I'm not sure.>>>>>>>>>>>>>
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Antoine,


Nice diagram, well done visually.


You have a Hunter, so I guess you have a Yanmar. Yanmar comes with Hitachi alternators. Regardless of its size, don't know if you've seen this, which has been posted regularly when Yanmar's alternators come up.


Good luck in your efforts.


******************************************


Hitachi/Yanmar Alternators: (by Maine Sail)

Some alternators though, such as those made by Hitachi and found on Yanmar diesels, are dumber than a pound of beetle poop. Actually, to the alternator, they are pretty smart but to your batteries and the speed of charging they are flat out stupid. Why?

Hitachi alts with dumb regulators, and some others, limit voltage but also reduce voltage based on alternator temperature. This is a self protective feature installed in the internal dumb regulator to prevent the alternator from cooking itself. Remember voltage is the pressure that allows more current to flow. So, if we reduce the absorption voltage, then we also reduce the current the alternator is supplying.. Any battery at any state of charge simply will not accept the same current at 13.4V that it did at 14.4V and as a result the alternator will run cooler. What do you suppose this does to your batteries over time.......?

The problem is that when cold you will get 14.3V to 14.4V out of the Hitachi but as the alternator heats up the dumb regulator begins to reduce the CV/voltage limit based on the alternators internal temperature. It is not uncommon to find a Hitachi alternator at 13.4V when hot. This is REALLY, REALLY DUMB....

If you have a dumb regulator, and notice the voltage dropping, it is likely a temp compensated dumb regulator. Get rid of it or plan to buy new batteries more often.

If you have a temp compensated alternator or a Hitachi alternator on a Yanmar you really are in dire need of external regulation if deep cycling a larger battery bank.

This is from:

http://forums.sbo.sailboatowners.com...d.php?t=125392

and these, too:

http://www.cruisersforum.com/forums/...on-125843.html


http://www.cruisersforum.com/forums/...or-142083.html

[aybabtme]

Originally Posted by john61ct

If you're happy to rely on the BMS as the one layer of automated defence against overcharging, and

also to have it be the daily cycling charge control regulator as well, then you're all set.

Just pointing out that is what you have.

It certainly is true that few have more, and if you are keeping an eye on the charging progress maybe that will be fine.

What additional automated mechanism do you suggest?

[john61ct]

First choice:

Originally Posted by john61ct

I would be **very** wary of letting the BMS control charging, unless completely separate failsafe protection devices are added.

Better IMO to select charge sources with solid controls to do what I want, and let the BMS do its main job, which is protecting against when those primary controls fail.

Otherwise, a simple HVC mechanism of some type? Victron 712's relay control might do if you aren't using it for something else. . .

[aybabtme]

Originally Posted by Stu Jackson

Antoine,


Nice diagram, well done visually.


You have a Hunter, so I guess you have a Yanmar. Yanmar comes with Hitachi alternators. Regardless of its size, don't know if you've seen this, which has been posted regularly when Yanmar's alternators come up.


Good luck in your efforts.

Thanks! Great info!

I'll be back on the boat in 2 weeks so should be able to confirm that it's an Hitachi. This information reinforce my belief that I should punt on integrating the alternator with this circuit for now. Although if it can only push 20A, then the Victron Orion-Tr would be more appropriate than the larger Sterlings, maybe? But I think I'll keep my money and invest in a new alternator if and when the need arises. Would you agree with this conclusion?

[aybabtme]

Originally Posted by john61ct

First choice:

Otherwise, a simple HVC mechanism of some type? Victron 712's relay control might do if you aren't using it for something else. . .

So if I understand you properly, you suggest adding contactors that are controlled by the Victron 712? Instead of those controlled by the BMS, or in addition?

I don't have a Victron 712, but the CCGX has similar connectivity that I could potentially use.

[john61ct]

If the BMS is doing the normal-use charge control then yes adding another HVC + contactor is needed for failsafe

[aybabtme]

Why do you think the BMS can't be trusted with that job?

[john61ct]

Not the point.

Everything fails eventually, and such fragile / complex electronics especially.

So should be planned for, at least all the various failure modes accounted for.

Contactors too, limited life if switching when amps are high, usually fail closed.

And not just scrapping the pack like overdischarge / LVC or fast charging while freezing temps.

Charging going high or long can cause **fires** that are impossible to extinguish

so extra caution needed there, can cost the boat or house, even lives.

Rather than HVC / OVP, maybe the failsafe protection could be overtemp, most BMS don't even do that.

I see "BMS" as a collection of functionalities, do not rely on just one monolithic gadget to do everything for you.

[aybabtme]

Thanks John for taking the time with the back and forth. That makes sense. Shouldn't be too hard to add at least one contactor controlled by the CCGX as an extra redundancy.

The Orion Jr BMS has 3 thermistors and does overtemp/undertemp protection. Can expand to more thermistors with an expansion module. I'm planning on putting the thermistors on the main negative pole, on the 4th cell's pole and then on the main positive pole. My idea being that the anodes/cathodes are conductive so would probably best carry and represent the internal cell temperatures.

[john61ct]

Sounds great.

If you can program the overtemp to cutoff charging low enough to catch either overcurrent or overvoltage pretty early that might be enough for fire safety.

But the bank itself may have taken a serious longevity hit by then, so personally I'd also put a redundant OVC in place.

OCP can just be a fuse of course.