LFP+BMS+Ultracapacitors? or (2)(LFP+BMS)?

[rgleason]

Could the appropriately sized and designed ultracapacitor bank provide protection for an alternator when a drop-in LFP battery BMS shuts down?

Would this possible solution be more expensive than having the (2) LFP + (2) BMS totaling the same capacity?

Reading https://maxwell.com/wp-content/uploa...ablization.pdf

Benefits of Maxwell’s Ultracapacitors in Voltage Stabilization
Maxwell is the global leader in ultracapacitor technology, development, manufacture and sales. Its ultracapacitors
have very high power capability, both in charging and discharging;
can charge and discharge rapidly and repeatedly. Depending on the specific cycle and operating environment, the cycle life can be in excess of 1 million charge- discharge cycles;
can have a lifespan of more than 10 years, with virtually no maintenance, when used in low-stress applications;
have a wide operating temperate range, usually from -40° to 65°C.

Further, ultracapacitors can be charged and discharged quickly and
repeatedly. A charge or discharge during normal operation takes only a few seconds. The cycle life for Maxwell’s products can exceed 1 million cycles. Such features ensure that the ultracapacitors provided by Maxwell can meet the frequent operation requirement of the cranes over a 10 year lifespan with minimal maintenance."

[sailorboy1]

I believe that a capacitor would be already charged and no much of a dump load

A properly set up regulator should never suddenly shut down LFPs from a BMS. If worried it will, set the voltage even lower to like 13.8V

[s/v Jedi]

Supercapacitors play a different role, they stabilize voltage down spikes caused by inrush currents at motors, amplifiers etc. Basically a super version of regular voltage stabilization after a rectifier.

To protect an alternator that has no “always-on” battery connected, I think this is the best bet: https://baymarinesupply.com/sterling...on-device.html

[rgleason]

Yes, of course. Sailorboy's first statement is right. Thanks.
Yes, the Sterling version S/V Jedi suggests, may be a better choice than the Balmar version.
Yes, ideally the alternator is shutdown before the BMS acts.. but the LFP batteries (particularly drop-in) will eventually get used up and one cell may drop, causing a BMS shutdown.

[SOLAR SUPPORT]

Originally Posted by rgleason

Yes, of course. Sailorboy's first statement is right. Thanks.
Yes, the Sterling version S/V Jedi suggests, may be a better choice than the Balmar version.
Yes, ideally the alternator is shutdown before the BMS acts.. but the LFP batteries (particularly drop-in) will eventually get used up and one cell may drop, causing a BMS shutdown.

LFP cell balance problem can progress very slowly over time without you noticing. In a marine environment where energy production and consumption are simultaneous, you may not have the opportunity to top balance the LFP cells every day, or the cells in the battery may not have completely identical characteristics.

When an accidental Hvcutoff occurs, if your alternator is connected only to the LFP battery, problems will occur with the alternator or your sensitive electronic devices that are currently on. The reason why I say "accidental" is that the previously set charging cut-off voltage of the alternator remained above the Hvcutoff voltage due to the disruption in cell balance and you did not realize it. LFP battery users, who believe or are convinced that this will never happen to them, start reading all the curses in their archives in the face of such an event.

In order to avoid this bad situation, your lead acid battery must be constantly connected to the alternator while charging the LFP battery bank with the alternator. The reason why super capacitors are not used for this job is probably because they cannot absorb the high voltage that occurs in the alternator stator in a very short time, like the LA battery.

[Fuss]

Originally Posted by rgleason

Yes, of course. Sailorboy's first statement is right. Thanks.
Yes, the Sterling version S/V Jedi suggests, may be a better choice than the Balmar version.
Yes, ideally the alternator is shutdown before the BMS acts.. but the LFP batteries (particularly drop-in) will eventually get used up and one cell may drop, causing a BMS shutdown.

It would be a good thread if someone did a what can be used for an alternator dump load thread.
I’m using the following so far
1. set the bms/s to disconnect higher than the alternator
2. set the alternator to disconnect lower than the BMS
3. have more than 1 battery paralleled
4. I have a mini agm also in parallel , not sure of the ah, might be around 2 ….i am not convinced that this works…but it can be used for testing alternator settings without having the lifepo4s connected. I might test sometime with an old cheap alt whether the mini agm absorbs a cutoff but even if it did, there are many other variables.

Side note…I think I read somewhere (I think I read somewhere!!…oh dear oh dear ..one of these I think I read somewhere forumites!!) that the sterling is only guaranteed for 1 protection …after this it needs a reset of some sort…. So don’t miss the first protection event…. If this is true then the sterling is also not a complete solution. But I could be wrong.
I just went to the link…it says….
Please note that this device is sacrificial by design: a severe voltage spike may destroy the device; the point is that the spike destroyed the device rather than your alternator.

[sailorboy1]

Originally Posted by Fuss

Side note…I think I read somewhere (I think I read somewhere!!

I just went to the link…it says….
Please note that this device is sacrificial by design: a severe voltage spike may destroy the device; the point is that the spike destroyed the device rather than your alternator.

I have an acid battery to take a spile. But I look at one of these Sterling 1 use things no different than a fuse that shouldn't blow.

[SOLAR SUPPORT]

This has been posted in an other topic

Quote:

Originally Posted by Letterkenny

I just finished my install. Went with Balmar 618 and LiTime 100ah mini batteries (4 of them). So far, so good. Fit my battery compartment fine on my boat and protecting my altenator with significantly more output than a DC to DC allows. I already have a battery isolator for the start so didn’t need to get a DC to DC. I find it hard to justify the Battle Born/Dakota/Relion brands. They aren’t keeping up with the densities that these other brands are doing and price is just outrageous.
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I can say that you are doing something right. I also used existing battery isolator. While charging the service and engine batteries from the alternator by using the Battery Isolator, you also create a one-way connection with the alternator for each group of batteries. With LA crank battery connected to the Battery Isolator, you protect all devices in your installation against accidental BMS Hvcutoff damage, not just once like APD, but constantly. When a battery isolator is used, it is also not possible to transfer energy between battery groups in the direction of discharge.

Does setting the alternator's External Regulator charging cut-off voltage below the BMS Hvcutoff voltage protect your system from bms Hvcutoff accident forever? Let's say you added APD to the system. You have one-time insurance.

When it comes to active marine use, it is not possible to balance the cells of the battery regularly every day. Therefore, the balance of cells can slowly deteriorate over months. If you are a careful user, you will take time to balance the battery cells and do it regularly at certain intervals.

However, sometimes cell balance can be neglected and the Hvcutoff voltage of a 12 volt drop-in Lifepo4 battery may drop by, say, 0.1-0.2 volts every month. Let's assume that the alternator external regulator charge cut-off voltage setting is set 0.5 volt below the bms Hvcutoff level. A user who is not very careful may be exposed to bms Hvcutoff accident after 3 - 5 months. Using a battery isolator eliminates this possibility forever.

[tanglewood]

When an alternator is producing output, then suddenly disconnected, doesn't it create a REVERSE voltage as the magnetic field collapses? So anything like a battery attached to "dampen" the spike is actually supplying current, not absorbing it? Or in the case of a diode-like device, it just clamps the reverse voltage at 0.7V or whatever fro the type of diode?


No?

[SOLAR SUPPORT]

Originally Posted by tanglewood

When an alternator is producing output, then suddenly disconnected, doesn't it create a REVERSE voltage as the magnetic field collapses? So anything like a battery attached to "dampen" the spike is actually supplying current, not absorbing it? Or in the case of a diode-like device, it just clamps the reverse voltage at 0.7V or whatever fro the type of diode?


No?

No,

The current generated at that time goes from the alternator to the LA battery. Already the battery isolator is there to forbid current flow from the LA battery in reverse direction.

[s/v Jedi]

Someone should test this on a bench.

[wholybee]

Serious question here. Has anyone on this forum actually had a HV disconnect cause a voltage spike that damaged the alternator and/or any electronics?

I know it happens. I know something should be done to protect against it. But with practically all LFP installations now being cheap drop ins(my guess), and most of those probably being done by owners that don't know better than to just swap them(my guess), I would really expect, if it is a serious concern, there to be many examples of it happening.

But, there are not. We have example after example of owners asking about what they need to do, or forum members telling them what they did wrong. But where are all the "I installed LFP and not all my electronics are fried" posts? What we have are a few highly respected technicians that have written doomsday predictions that it will happen if you don't add the protection. But outside of a very few cases those professionals cite, it doesn't seem to happen.

My evaluation, and I think this is very realistic, is this:
In order for a damaging load dump, a couple things need to happen. First, there needs to be a disconnect. It doesn't need to be a high voltage disconnect, it just needs to be sudden. Second, the alternator needs to be producing a high current when it happens. That means bulk charge rate. If a high voltage disconnect happens, the current is probably pretty low at that time, unless the alternator regulator has failed and it is trying to pump out 15, 16, or higher volts. But if the alternator is set at 14.4, and the cutoff happens at 14.3 when an out of balance cell goes high, then the current isn't going to be high enough to create an issue. You are moments away from current dropping to near zero and charging stopping anyway.

To cause the load dump, you need a more exceptional situation than simply having a HV cutoff. Something that would cause a disconnect when the battery isn't fully charged, and your alternator is putting out 70A or 100A or more. Those happen, for sure, but are much more rare than a HV disconnect. Maybe a low temp disconnect if charging in freezing temps, or if you have a FET BMS and you exceed max charging current. Or if you program the BMS to cutoff at a really low voltage compared to what the alternator is set to. But those are really system design and setup errors.

[maine-cruiser]

Originally Posted by s/v Jedi

Supercapacitors play a different role, they stabilize voltage down spikes caused by inrush currents at motors, amplifiers etc. Basically a super version of regular voltage stabilization after a rectifier.

To protect an alternator that has no “always-on” battery connected, I think this is the best bet: https://baymarinesupply.com/sterling...on-device.html

Anyone ever disassembled one of these? I'd have to think that at its heart there's a TVS diode to clamp the spike. I have a TVS diode across the terminals of my alternator (which feeds LiFePo bank directly).
Littelfuse has some info on load dumps and TVS diodes:
https://www.littelfuse.com/media?res...-sld-datasheet
https://www.littelfuse.com/~/media/e...n_note.pdf.pdf

[CarlF]

Originally Posted by wholybee

Serious question here. Has anyone on this forum actually had a HV disconnect cause a voltage spike that damaged the alternator and/or any electronics?
.

I can add several additional possibilities to the ones you list as to why we see so little actual damage from BMS disconnects with drop-ins

1) Drop-in batteries don’t get way out of balance easily because they are normally connected in parallel. Series wired batteries are much more prone to persistent balance problems.

2) To damage an alternator, all of the drop-in batteries need to have their BMS disconnect at the same time. One drop-in BMS disconnecting won’t cause a spike.

3) Most modern alternators have improved avalanche diode designs that can survive a disconnect.

4) Most boats have small charging capacity way below 1C hooked to a large battery bank. So a BMS disconnect due to excessive charging amps is unlikely. A good alternator regulator won’t permit over voltage if properly programmed.

5) Most installations have a DC-DC charger to the lead acid start battery and/or alternator protection device.

I believe BMS disconnects were much more common in the early days when most owners were assembling their banks from individual cells and using a single BMS.

[SOLAR SUPPORT]

The video link below explains the use of battery isolator and informs about his own experience.

https://youtu.be/i17__iMSaf4?si=EdrlgcfqNWyNi7kw