Instruments get fried when starting the engine.

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I have a generator that supplies power to 3 battery chargers, one is solid state, one is a mag resonance charger and the other is a simple transformer type with rectifiers. 120v AC in and 14.4v DC out.

When I start the engine while the generator is running the instruments get fried and I was wondering if any of the chargers were producing some form of spike caused by the starting load of the engine.

The circuit that gets fried is a quad OP295 op amp that has its power supply direct on the 12v line out from the batteries.

The main reason this is serious is because we are just about to fit a unit that draws around 600 amps and may be used up to 10 or 20 times for about 5 seconds at a time in a window of say 5 minutes. This kind of load on the batteries requires the chargers are all running to keep the volts up but will most likely fry the instruments again. OR worse it could fry other more expensive stuff.

So does any one have any ideas as to what may be happening, can spikes occur?

Many thanks

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Here is a quick diagram of the circuit that goes down.

If any body has any ideas what should be done to the Vc to smooth out any transients? If that is even what is causing the problem.

View attachment 66301

 

[Nigel Goodwin]

The circuit seems utterly lacking in any protection?, you should add the usual in-car type protection to prevent spikes - LC filtering on the incoming supply, and a zener diode across the power rail to clip soikes.

 

[Quantised]

Hi Nigel. Thanks for the input and as you say it is unprotected. So would you be so kind as to explain in-car protection?

Any guidance on what LC filter values would be appropriate as well as size and power rating of the zener.

I know it is bog basic stuff and hope you can help.

Best

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[chemelec]

here is a quick diagram of the circuit that goes down.

If any body has any ideas what should be done to the vc to smooth out any transients? If that is even what is causing the problem.

View attachment 66301

very strange looking circuit!

 

[Quantised]

very strange looking circuit!

Hi chemelec
What particular parts are strange? All comments well received to try and improve on this. It is supposed to be a pair of voltage followers and then a gain stage followed by a line driver with some way to change the gain to meet the meter it drives. It may not be elegant but it did work well for a while till we had those nasty spikes. (Well we assume it was spikes but that is still out with the jury)

I am interested to know what sort of spike can be caused when a simple transformer/rectifier gets dropped from 13.5 volts to 7 volts by a starter motor, is there some huge emf pulse that occurs????

Best

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[ronv]

Can you draw a little sketch of what you have? 3 chargers charging 1 battery? A motor generator??

 

[4pyros]

I have a generator that supplies power to 3 battery chargers, one is solid state, one is a mag resonance charger and the other is a simple transformer type with rectifiers. 120v AC in and 14.4v DC out.

How is this all wired up?

 

[dr pepper]

Pulling hundreds of amps or even tens of amps over long supply leads can cause resonance esp if the current is sudden from a contact or solenoid like a starter.
A 47mH choke on the power supply might do some good, and a differential type choke to take out hf, the 47u C needs to be a low esr type, and maybe a 1000u.
A transzorb accross the supply would be a good idea, you can get them down to 36v.
If the starter creates ridiculous noise (and some marine starters do), then think about connecting up a relay so power is removed from the circuit while the engine is started.
The last ferroresonant charger I saw had polished brass meters on it and belonged in a museum, there are a couple of diffo types, if what you are doing is permanent and part of a business then consider buying yourself a set of chargers all the same.
I suspect however that something mad is happening due to the way you have all this rigged up.
What pulls 600a?

 

[KeepItSimpleStupid]

This should give you an idea why your circuit fried: https://www.electro-tech-online.com/custompdfs/2012/08/autotransients.pdf

 

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ronv and 4pyros - I have attached a basic layout of the batteries and the chargers. The main AC and DC distribution panels are not shown nor is the negative or isolation switches for simplicity.

600A motor duty - on 10 ro 20 times for 5-10 secs in a 5 mins period
350A motor duty - on for up to 30 minutes
200A and 250A motors duty - on for about 2 minutes
Only one motor is ever used at any one time and normally once a day to once a week.

Keepitsimplestupid - many thanks for that link as it is exactly what may be going on here. We try hard not to load dump the alternators by turning off an isolator switch BUT it could happen one day I suppose. It seems the inductive load is the one I need to concentrate on.

View attachment 66362

 

[Quantised]

Pulling hundreds of amps or even tens of amps over long supply leads can cause resonance esp if the current is sudden from a contact or solenoid like a starter.
A 47mH choke on the power supply might do some good, and a differential type choke to take out hf, the 47u C needs to be a low esr type, and maybe a 1000u.
A transzorb accross the supply would be a good idea, you can get them down to 36v.
If the starter creates ridiculous noise (and some marine starters do), then think about connecting up a relay so power is removed from the circuit while the engine is started.
The last ferroresonant charger I saw had polished brass meters on it and belonged in a museum, there are a couple of diffo types, if what you are doing is permanent and part of a business then consider buying yourself a set of chargers all the same.
I suspect however that something mad is happening due to the way you have all this rigged up.
What pulls 600a?

Maybe able to find a 47mH in an old TV or something else thats scrapped but without a local electronics shop it may have to be sent in from overseas. Tranzorb as well.

If the motor is started on its own there is no problem, it only occurs when the the chargers are on as well. So I had presumed the chargers were reacting to the starter motor load.

Ferroresonant chargers have some good characteristics, they are simple, reliable and slope off the charge at 13.8v so can be left on without boiling the batteries.

I would love to get new chargers but thay are around $6K for a solid state one and although the xfmr charger is really heavy it does allow the batteries to be equalised as it pumps out 50amps at 16v so the variety is quite useful.

The 600A pull is from a bowthruster, never had one before and thinking of putting one in to aid in 'parking' but concerned it may cause problems after this recent incident.

 

[ronv]

Only a guess, but it could be one or more of the chargers overshoot after the load is removed. You would think the batteries would clamp it pretty well so the first thing I would suggest is to get the 12 volts and ground directly from a battery not a charger. If the logic circuits are few (Not much current) you could add a resistor in series with the 12 volts like the diode. 15 or 20 ohms might be okay. Follow this with another big filter cap. If you can find a 15 volt zener that might also help. At least if it pops we would know we're going in the right direction.

 

[Quantised]

I suppose the load is only a few tens of milliwatts so adding a resistor and a cap seems reasonable, maybe the zener can go after the resistor and in parrallel with the second cap. Pretty sure I have some beefy zeners I can put in series to get 15V. Also thought I would throw in an inductor to make sure till I can get hold of a tranzorb.

This covers the small instrument circuit but how do I find out and protect the other stuff, there can be dozens of sensitive equipment connected at any one time like GPS or radar or stereo ...

I am thinking that the load drops the voltage on the transformers of the 2 chargers with them and then as you say it overshoots. The big charger pushes out 150A at 12.5v and drops to 100A at 13.5v so if the voltage is dropped to say 7v the charger may want to put out over 200A or even more. When that start cycle ends the overshoot could be huge. Cant measure it though as I do not have a storage scope, except to fry a couple of zeners!!

 

[ronv]

The voltage has to go above 36 volts to blow the op amp. I'd be suprised if the batteries would let it go this high so again my guess is that you are getting the voltage for the circuit from the charger end of the cables and not from the battery posts. Can you confirm this. Maybe if you can come up with the 15+ volt zener we could put an led in series with it and "see" the overvoltage if it lasts long enough. Then you could kind of probe around.

 

[Quantised]

The power to the engine comes direct from the posts of a pair of 220AH batteries and the instruments are connected to the engine harness which comes from the +ve line on the starter motor. It does not come from the chargers.

The wiring from the chargers goes first to the 700AH deep cycle batteries but as they are deep cycle they have a high internal resistance then they are cabled to the start batteries by a good few meters of cable and that is where the engine take off is.

Maybe the deep cycle batteries cant assorb the pulse as they are very high resistance compared to the start batteries but they alone should absorb the pulse.

OK so a 15v zener and then an LED and do a start - right. See a bright flash and ......
New diode and turn off ferro charger and do it again. etc etc till we see the culprit.

Seems a good idea and easy to do but when done - what then?

 

[dr pepper]

I have a boat, it too has a bow thruster, but it doesnt pull 600a, its 1.5 hp, so more like 90a, it generates a fair bit of noise too.

The thruster is up front while the engine which has an attached 240v ac genset powers 240vac chargers fore and aft.
The thruster is obviously right at the front while the main engine and domestic batteries are in the stern quarters, I have a 3 stage ac charger for the domestic batteries at the stern, and there is a dedicated ac charger for the bow thruster battery which is right at the front, it was cheaper for the thruster to have its own battery than 50mm2 or so cables run from the stern, the engines batteries are charged from its alty.

In your situation, and maybe others here will agree is to have a seperate power source altogether for your engine instrumentation, a small 12v lead acid battery maybe 2ah, or even aa's, and recharge these from the engines battery, as I assume you only look at the instrumentation while the engine is running, you can get 12/24v chargers off ebay for little cash.
Then your instrumentation would only be associated with the engine electrics not the vessels, which should sort things out.

Sounds like you have connected deep cycle and engine batteries together, not a good idea, really your engine batts want to be seperate, I spose that would mean expense on more deep cycles to power the thruster.
If you dont have domestic loads that much then all engine batts might be better next time you need new ones.
Long leads and heavy loads are an invite to noise, the inductance of the leads causes ringing, but theres no way round that either if the thruster is a ways off, you can get fat ferrite torroids, but I've never seen one you can run a 100mm2 cable through a few times.

 

[Quantised]

Your setup sounds familiar with a battery up forward and a good way to go but I dont think a huge battery up in the bow would be easy to fit and the balance might go a bit too far forward.

The instruments are part of the engine harness and so quite difficult to seperate. But that can be easily accomplished by just isolating the engine start battery. However the batteries are normally ganged together so whichever engine/genset is running it charges or floats the whole set. Also the big eng alternator helps supply some of the bigger loads so that was the main reason to gang it all together. Better rethink that.

When not running any engine the batts are eperated to 2*700 for the house, 1*700 for navigation equipment, bilge pumps and emergency items. The start batts are then OFF. Basically any charger can be switched to any battery and this has developed like that over years because this is a working yacht and some days we can get 80 to 100A house loads in the evening when all the lights go on in the canins and pumps and fans etc etc.

Not sure about running the house of engine batts as cycling them kills them in a year or so, the deep cycle ones last 10 years with a 100% discharge every 2 days so you can punish them somewhat.

Here is a thought, genset on one batt, engine on the other batt but the 2 batts are ganged together. Do you think the start load of the engine will look like a disconnect to the alternator and so it does a load dump? or an overshoot?

 

[KeepItSimpleStupid]

In a car, generally all unneeded loads are shed while starting. I think the only one that isn;t usually is the headlamps. Probably because a lot of them are on a separate circuit. Years ago, an American can had a thermal built into the headlamp switch. My foreign car, has a fuse for each beam.

If there is a way to "disable" the charging system while the "START" button is pressed? This could save a lot of headaches. For one, the alternator can see the low voltage and in essence say, I need to charge. This puts a larger than necessary load on the engine for starting.

 

[Quantised]

It is not so much the start that is the concern - it was just that this happened to highlight the problem. For this we can leave the engine isolated from all the other batteries until it has started and then gang it in.

The main issue is when we add the bowthruster which will blip 600A and cause similar spikes. Cant really drop all other loads as that would mean things like the GPS, instruments as depth, wind speed and direction, radar, lights, power steering etc would get cycled on and off which would be a disaster.

So if I did this below and seperate services onto differant circuits it may help with the pulses but it loses out on performance as now the engines 200A alt and the gensets 50A alt plus the 80A ferro mean we lose 330A of charge and so the bowthruster will see a much lower voltage and so lower performance, it is a bit on the shy side anyway and could be bigger but that is the largest 12v one that is made.

But the negative line is all common so can the pulses go through this route. Isolating the negs is not possible.

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