LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

[dlentz]

Originally Posted by goboatingnow

does anyone do stock alternators in high capacities that have the Diodes external ( and the regulator as well obviously). Id like to buy alternators without any electronics onboard

Dave

Try these guys, I used one in a DC genset. Well built and priced very reasonable. Unlike typical Marine alternators, these are rated at 100% duty cycle. High Output Marine Alternators by ZENA, Inc.
Dwain

[ConradG]

Originally Posted by dlentz

Try these guys, I used one in a DC genset. Well built and priced very reasonable. Unlike typical Marine alternators, these are rated at 100% duty cycle. High Output Marine Alternators by ZENA, Inc.
Dwain

Yes, my 250 amp Zena has external rectifier. I just fabricated the bracket, serpentine drive pulley and tensioner last fall and have only welded with it. Doesn't overheat while welding full power but that's not like filling lifepo4s I imagine. The diodes are mounted on large heat sinks and there's a 12v fan on the assembly. It can mount wherever you feel comfortable running the 3 phase ac power. I fused at the alternator and both ends of the dc lines (battery and rectifier). You can use any regulator ("smart" or otherwise) and they sell one that is inexpensive and adjustable for cutout voltage sensed at the battery with alternator temp sensing. They also have an over voltage protection module that shuts off the controller at any given voltage in case a regulator doesn't do it's job (manual reset). The controller is external so its easy to have a manual switch to excite/de excite the field. I put one at the helm (via relay) in case I need full power to the prop. When I go lifepo4 it will be my bms if the cell level over voltage alarm screams! The controller, over voltage protection module and regulator are sealed solid state units meant to take the elements, tinned wire. (These things are usually mounted on trucks and equipment or welding). The welder is pure dc and a dream to use! Stick and wire feed. Constant power even to mig aluminum for which it has to be! Impressed so far. Will be interesting to see how it does on lifepo4. Oh, and the output of the alternator is adjustable in case you want/ need to derate it to control overheating or lessen the load on the engine.

[FlyingCloud1937]

Originally Posted by goboatingnow

does anyone do stock alternators in high capacities that have the Diodes external ( and the regulator as well obviously). Id like to buy alternators without any electronics onboard

Dave

Leece Neville also has an external Rectified alternator, as a matter of fact most of the 4800 series can be externally rectified.

I have a custom built externally rectified alternator that is 240v volt 3 phase that goes to a custom built toroidal/rectifier back to 12v nominal.

I designed it for bat banks that are in excess of 30 feet one way from the alternator, it's a 12v wound field lundell style that uses a balmar 612 regulator. So instead of 2 X 4-0 pos and 2 X 4-0 negs I use 3 # 6 between the bats and the alts.

The beauty is the high voltage stator runs at close to 90% effy... and the the total of the system is in a range of 80%+. I'm now in the final stages of Caterpillar Certification.

Now with LI-ion, coming into the market, I'm looking at a a 3 phase toroid.. that can do 4 isolated buck.. to 4.2v, and with an added SCR w/battery sense to manage LI bats.


Lloyd

[bill good]

Question for all.
A question on alternators. I ask opinion on disconnecting the battery to alternator. Would like to use a standard unit without changing the internals. The problem appears to be the unfiltered voltage with ripple exceeding the ratings of diodes & regulator. So I ask why not add electrolytics somewhere in the range 4000uf to super cap range to the B+ ? (The Z of a 4400uf/25v seems low enough.)This idea is to do with being able to cutoff the charge when lifepo4 batts are near where I want them.

Regards Bill.

[CharlieJ]

Bill Good-It is not clear to me what problem you are trying to solve. LFPs can absorb some really sloppy DC and a properly set up charging source with or without a BMS will stop the charge at the appropriate point.

[ebaugh]

I think he wants to disconnect the alternator from the battery bank, but still have something for the alternator to see. Capacitors sound like a reasonable idea, but I don't know if that will keep the alternator happy or for sure if the caps will take the transients. The right caps will be OK I think if rated for twice or more the bank voltage.

[CharlieJ]

Thanks Bob. In that case, simply have the BMS open a relay in the B+ to the alternator regulator and the alternator becomes a idler.

[bill good]

I am thinking there is no case to try & float charge a battery at 100% SOC. It is a bit like trying to add more fuel to a full fuel tank. Any opinion on the value of a cap?

(It is prob. not a good idea just to use a BMS to open the link alt-batt)

[hellosailor]

The amount of ripple and other distortion from any functioning alternator should not be a problem for any diodes, any regulator, any battery.

In fact, there are some oscilloscope photos on the web from a ham who took a look at the DC output from his Honda genset. Honda says it is for battery charging only, that it is not clean enough to power DC equipment, and it is indeed ugly.

But that's what batteries, diodes, and regulators are designed to work with. As long as you don't exceed their maximum ratings, it really doesn't matter how clean or ugly the supply is.

Certainly you could install a massive bank of toroids, coils, capacitors to try making alternator output into nice clean DC but there's no point to it. More stuff means more ways you can have failures. If there's really anything wrong with the output, FIX THE ALTERNATOR. Really.

[ebaugh]

The problem with a Li Ferrous bank is a justifiable need to disconnect all charging sources in the case of over voltage, or I think in Bill's case simply a fully charged bank.

The old school of marine electrical says you can't simply switch the battery out of the circuit or the alternator will fail. I think the diodes are the rumored weak link. I don't know if this is an issue or not for modern alternators. But I can see the issue where if the controller is too slow to react, the alternator will run away for a moment exceeding the voltage ratings on the diodes. At least that's how I think of it.

I agree with Charlie, the safe answer is to remove the field current, the easiest way to do this is pull the plug on the external regulator or the field wire. Or like I do, keep a second battery in the circuit.

But some alternators don't have controllers with easy access to the field or power circuit, So the question I see Bill asking is will the caps provide a buffer for the alternator controller to ramp down before the diodes see a transient above their rating, I just don't know. Probably depends on the alternator controller combination.

To be absolutely safe, In Bills case, removing the field directly or via the alternator controller power is the safest solution to eliminate the charging. Then simply turn it back on to resume charge when needed.

[CharlieJ]

(It is prob. not a good idea just to use a BMS to open the link alt-batt)

Absolutely correct! You will fry the output diodes in the alternator. My recommendation is to open the B+ supplying power to your external regulator. This is, in fact, Balmar's preferred way of taking an alternator off line and is exactly what we do when we shut down an engine!

With some careful set up of the "float voltage" of your charging sources, you will stay off of the steep part of the knee and no current will flow. I have 16 CALB SE180 AHA cells in my shop in a 4P4S pack. I have hammered them pretty well on discharge but only have a 60A charger. Setting the charger float @ 3.35VPC gives me between 90 and 100% SOC. The charger sits there and the pack absorbs no more than 0.5A

I am setting this pack up to float. I think that to terminate the charging sources and then wait until the pack's SOC comes down to some level before turning on the charging sources is too problematic from a control standpoint.

As usual, out here on the bleeding edge, YMMV.

[daddle]

To the point, a capacitor across the alternator output will not have any useful function.

[bill good]

OK I need to supply more info!! Boat has 2 X 7.5HP Yanmars Prefer to keep standard alternators if I can. There is a point of view that any voltage external to the cell "may" contribute to problems within the cell & since the self discharge is not an issue why take any chances with float charging. Except for one batch of faulty cells the only other failure mode that I can trace is where charging is involved. To my way of thinking a simple addition of an external electro is not only cost effective but universal to any alternator with internal regulation & no ext field connection. That is why the idea is on the table.

Regards

ps daddle tks to a B+ of an alternator a battery is an equiv. large capacitor which does the filtering & adding a suitable value of capacitor maybe provides the same filtering. Well thats the thought!!

[FlyingCloud1937]

Originally Posted by bill good

Question for all.
A question on alternators. I ask opinion on disconnecting the battery to alternator. Would like to use a standard unit without changing the internals. The problem appears to be the unfiltered voltage with ripple exceeding the ratings of diodes & regulator. So I ask why not add electrolytics somewhere in the range 4000uf to super cap range to the B+ ? (The Z of a 4400uf/25v seems low enough.)This idea is to do with being able to cutoff the charge when lifepo4 batts are near where I want them.

Regards Bill.

With the value of a LI bank it seems more then prudent to invest in a proper alternator.

It's not the ripple, it's the voltage spikes caused by the collapsing of saturated magnetics that fries the diodes. Some alts use avalanche diodes and can support an accidental bat disconnect. But they won't sustain a continued abuse, such as they are regularly switched.

Also you have to be careful if you are on the bleeding edge of the voltage top of the bats, as some alternators will continue to produce Volt/Amps from residual magnitisim without any field excite.

Lloyd

[FlyingCloud1937]

Originally Posted by hellosailor

Certainly you could install a massive bank of toroids, coils, capacitors to try making alternator output into nice clean DC but there's no point to it. More stuff means more ways you can have failures. If there's really anything wrong with the output, FIX THE ALTERNATOR. Really.

Just for the record my use of Toroidal Transformers is not for ripple management. I use prior to rectification for bucking voltage back to battery voltage from high voltage custom wound stators.

I a now working on a design to use toroidal transformers to manage Li-banks, coupled to SCR's where the alternator is controlled by the pack voltage, and the individual bats in series are controlled by isolated Trans/SCR's with individule voltage sense, so as to charge each cell to it's required voltage.

Lloyd