Battery fuse blown = wrong voltage reported by LynxBMS

DIY
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1

System consist of:

Lynx Smart BMS NG , two 24V, 200Ah batteries in parallel, Multiplus-II 24/5000

One of fuse batteries blown (reason not found but not important for this issue).

As a result we had wrong battery voltage reported in system by Lynx Smart BMS.

in “Individual battery Info” battery #1 was 28,99V, battery #2 26,65V - battery #2 had fuse blown :frowning:

Lynx reported to the system 27,82V - which is average value of two voltages above.

Charging voltage in Multiplus is set to 28,4V, but since BMS / DVCC share voltage, Multi had as a reference value 27,82V and was forcing charge voltage until 29V on battery - than we got multiple alarms ATC/ATD failure.

No other charge source was active at the moment - only Multiplus.

Also temperature is average - so owner see 39 Cdeg while one of them has 43 Cdeg and second 34 Cdeg.

Some additional alarm about parallel batteries voltage difference would be great solution for such a problem. +/- 0,2V difference on parralel batteries is always a problem. ?

Printscreens below show different values because i made them later. But numbers still shows the problem.

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2

Because of the way DVCC works, battery aggregation is normal. DVCC needs one data point to work with. Even within a single battery their can be variance in cell temperature across the battery - so usually just the highb and low are sent+ the cell high and low so you can check trends.

In fact its normal for almost all manufacturers such as pylontec to do the same. I have often tested banks that have variances in them.

Each battery should self manage though. And it is pretty important to try get current sharing as close as possible.

Also temperature is average - so owner see 39 Cdeg while one of them has 43 Cdeg and second 34 Cdeg although these things would normally be Investigated by an installer. Maybe terminal torque or something is not right.

FYI fuses can blow because they ran hotter than expected. So 2 of the same value with the same load the hotter one will blow first.

3

Yes - battery agregation is OK. Of course within single battery cells also can have different voltage, and for particular battery You will get an information about slight cells imbalance. But you will never get any info that one of paralleled batteries in bank have voltage difference >1V !?

It is not possible to have any Voltage difference between parallel connection of few batteries. It can differ only by voltage drop in wires + measurement error. If it differs it always shows connection problem or electronics for measuring voltage in battery.

About temp - let say maximum charging current is set to work with full battery set. Let say system is perfectly set, and while all is OK battery temperatures are within 35-40Cdeg, current per battery is also proper. When fuse will blow or connection gets loose all current will go to only one battery and also makes this battery hotter than usual. But in main screen will show improper voltage and temperature readings.

When disconnected battery will cool down to 25deg, then while still connected battery has 55Cdeg You will still see 40Cdeg. You don’t get an alarm about battery temperature until BMS shuts OFF when working battery will be at its temp limit.

Nice if it’s normal for other manufacturers, but can’t it be better?

I don’t mind battery aggegation, but simple detecting voltage difference and presenting some alarm would clearly show a problem in battery connections. And as I see in my system, blown fuse cause a problem for other batteries by overcharging them.

This kind of detection would show the problem very fast, before user will notice strange behavior of the system.

You write “Each battery should self manage though” - I’m talking about diferrences between batteries in bank - not cells within one battery. Battery will not self manage replacing the fuse :thinking:

For big systems like 5-10 batteries You will probably never notice a problem of blown fuse. Any alarm about batteries imbalance (not cells imbalance) would help to start searching for the problem before something more serious happens.

FYI fuses are designed to blow when they are hotter than expected :slight_smile: - this is operating principle for the fuse. Current flows thru fuse, and heats it acc. to Joule integral (I^2*t) . When fuse is too hot - it blows.

4

Correct which is why aggregates exist.

1v deviations now are different.

Correct, so why was yours hot enough to blow?

But battery will have its own protection (self managed) and shut down if over temp even if you only see an aggregate.

No. But a fuse blowing now needs attention from a sentient being, because it means there is a problem.

Which is why a lynx system has monitoring on them. Again it should be an unusual event for a fuse to blow not a normal thing.

Seeing 40°C would freak me out anyway. Would still be looking at it. There are highs and lows in vrm advanced (if the battery reports it) so you would see the high and the low and work out if one in particular needs attention.

If more in depth monitoring is desired there are ways to achieve it.

5

Yes - Lynx system has monitoring on fuses - in Distributors. But to detect fuse blown it needs to “see” voltage difference input to output of fuse. Please check manual Lynx Distributor M8 and M10, page 6. Thats why for batteries You use PowerIn. When fuse breaks there is still battery voltage in the output of the fuse. Fuse monitoring simply don’t always work for batteries. It will work when battery with broken fuse will have much lower voltage than busbar. Fuse monitoring is great for loads, but for batteries not so much. Probably that’s why all the Victron drawings show Power-In for batteries and Distributors for the rest.

If 40°C freaks You out please visit working Yacht in Greece, Carribean etc in mid season. 35°C outside and batteries still have some job to do. If yacht owners would freak out because of these temperatures they would need to use their yachts only at winter time :). Operating temperature is up to 50°C. I always suggest to clients to use some small aircondition for battery, but it’s not always possible. Anyway +40°C is quite normal :hot_face:

Since it is physically NOT POSSIBLE to have voltage difference than why You need aggregation? If all batteries are connected to common busbar they simply MUST have the same voltage. Why there is a need to calculate average of 10 of the same values, and at the same time don’t care that one of them don’t match others? It simply MUST be the same +/-1%. If not = something is wrong.

In the end it was not a broken fuse. I helped him online only - he gave me wrong information in the beggining. It was very poor quality fuse holder (not lynx type). Nut got loose and wire disconected. Fortunately he didn’t have more serious problems.

I also sometimes saw fuses that was bended. When installers are careless during mounting of the fuses it can bend while tightening, then fuse will not have proper parameters anymore.

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Also loose connections in yachts is not unheard of. Vibration during engine working can do a lot of problems like loose connections. For big ships standard maintenance work is to check electrical connections. For yachts nobody will do it of course…

Just to summarize - I’m thinking if there is a way to show this idea/problem to Victron? Since Lynx Smart BMS is already calculating average voltage of all connected and monitored batteries it should be quite easy to check at the same time that one or more battery voltage don’t match others. Since this would be nice and easy way to see blown fuse or wires problem, and produce an alarm before something more serious happens. I prefer to think what can be done for the future, rather than bother why someone used fuse holder from 3D printer :sob: :scream: .

He had money for Lynx Smart BMS NG and batteries, but nothing left for Lynx PowerIn? :joy:

6

If it is mentioned here, it will be noted, especially if other people add that they would like it too.

In the meantime there are smart battery senses for connecting to and checking each one.

It a boat i imagine there should be regular system checks. Even if it is the owner or person who works for them.

Many batteries also aggregate their own voltages.

For example i know a few manuafacturers using 16s. They take low cell x 15 + high cell = xxx And sometimes it is not even what is measures at the terminal.

Crazy. Especially considering that their lifspan is affected.

7

Yes, but seems like we still talk about something different. You are talking about cells in series in battery. These can vary because of of number of reasons. That is why balancing of cells is needed/ I’m talking about parallel connection of few batteries - each of them MUST have the same voltage on terminals, while cells still have different voltages. This below is of course exagerated, but still true:

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BT1, BT2, BT3 will always have the same voltage on terminals, while they are connected in parallel. Cells inside of each battery is something different, and this is solved by balancing, and proper information in the system.

Crazy. Especially considering that their lifspan is affected.

haha - yes it is crazy, battery lifespan is affected, but with the money they spend on yachts, it’s meaningless.Changing set of bbattery every 4-5 years is barely noticable next to other costs of maintenance

I work too long in yacht business to belive that. It’s like people who check oil level every week or even a month. Toyota even had in their manuals to check it with every refueling. I belive some people do it, but I never met one :joy:

8

A similar thing happens between batteries as well. Ohms law and a few others in the mix.

So they cna be supplied with the same voltage but not necessarily be at the same voltage (as you discovered a blown fuse can change that). If the charger is only on one end of the bank. So hopefully the yatch set up has take off from either end.

9

I don’t understand. How would You possibly explain two or more batteries connected in parallel having different voltage on each battery?

The only difference can be because of voltage drop in wire connecting battery to PowerIn. What else could it be? And how big voltage drop would we possibly expect?

If fuse is blown, can we still say they are connected? In my opinion when fuse is blown, this battery is no longer connected to bank, and only then it can have different voltage than other batteries.

That what it’s all about - showing voltage difference between batteries in bank would show that there is w problem with parallel connection - fuse is blown or loose wire.

10

On major cause isworkmanship, such as different crimping and different lengths of cable to each battery.

In parallel there should only be small differences uness there is a problem.

Internal resistance of the battery itself, the bms can be slightly different, small wiring differences. Different torque on each connection.

VIR relationship is very important.in bank balance.

If the bank also is not kept at a gigher voltage for long enough as well, these differences become more apparent