24vdc system surging and destroying electronics

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Old 07-13-17, 04:00 AM
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Question 24vdc system surging and destroying electronics

Hi,

I have a boat with a 24v system. I recently purchased a Wirie WIFI and GSM system which is fine on that voltage. Since I purchased the unit 12 months ago I have fried 3 units. I have discussed with the manufacturer at length (who replaced the first 2 under warranty) but I haven't resolved the problem. I am not an elecrtrical expert but i can find my way around the basics. The only common denominator I can find is that it seems to happen when I start my engine. I multimeter tested and I seem to have consistent voltage. I set the multimeter to lock the highest value and started the engine several times. I didnt see much more that a 1v increase. Within the range according to the manufacturer. After I destroyed the first unit, I installed a 24-12v stepdown which also fried on the second occasion. I installed a fuse between the power supply and stepdown and another fuse between the stepdown and Wirie unit. It still fried both and didn't blow either fuse.

I have just ordered my new replacement I would love to solve this probelm before it is installed. (My current plan is to disconnect the unit before engine start, until this is resolved).

Over to the experts!

Cheers

Steve
MV Friesland
 
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Old 07-13-17, 04:55 AM
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You sure it isn't under voltage when the starter turns over. That can momentarily increase the amps being drawn. Cars have a lock out in the ignition switch that disconnects most things when starting. Maybe your idea of disconnecting everything when starting isn't a bad idea but why not two batteries and an isolator. Not close to being an expert so just consider these random thoughts that may be wrong.
 
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Old 07-13-17, 06:29 AM
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There are DC to DC voltage stabilizers such as this one that might help.
 
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Old 07-13-17, 06:32 AM
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Note: Power surges and power dips usually do not blow fuses or trip breakers.

Only if a device or appliance that is running at the time of the surge should draw more current in response to the surge will the fuse blow.
 
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Old 07-13-17, 09:24 AM
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Is there a house battery? Or, are you running electronics off the starting battery? There is liability in having Electronics on during an engine start. Lots of bad transients caused by the inductive nature of both the starter and the solenoid. And, the bad stuff is not the simple voltage sag during high current flow, its the spikes at starter motor turn OFF. These pulses can be in the micro second range, and are viewed by a one-shot storage scope. Sorry, the max hold DMM won't do it.

So, filter the electronics, or run a seperate house battery. Newmar PC-10 might work; but, I've done my own with torroid and TVSS devices; depends on your level of DIY. House battery works for most boats over 17 foot or so.
 
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Old 07-13-17, 12:08 PM
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Thanks Telecom Guy.

I am running a separate bank of house batteries. The starter battery is separate so I am confused as to why it seems to influence the outlet. I should mention that I am running an identical stepdown transformer (from a similar 24v outlet) to run the satellite dish and it does not seem to be affected by the engine start. Why one and not the other? A voltage stabilizer as you and Pilot Dane suggest may be the best option but I guess I will have to find out the hard way if this works.

Allanj - that explains a lot - thanks!
 
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Old 07-13-17, 04:35 PM
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So, these devices that are failing are not run of the starting battery. hmmm. How is the house battery being charged? Is there an isolator or a smart relay to connect both to the engine alternator? There should be no way to get a spike from the engine battery bus to the house battery bus.
Do you have a solid connection between the start battery and the house battery NEG side? What engine? What batteries? If you disconnect the house battery, do the 24V electronics switch off immediately?

And, you see a 1 V increase during/after engine start. Is this just the voltage jump due to charging after engine start? Actually, 1V is too low an increase in a 24V system.
 
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Old 07-13-17, 04:46 PM
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Actually, 1V is too low an increase in a 24V system
It may not be depending how many batteries the system needs to recharge.
It may rise slowly at first.
 
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Old 07-14-17, 12:43 AM
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I am sure that the house batteries are completely separate as a friend who is an electrical engineer showed me where the charging system once connected both house and starter batteries. He isolated it completely due to a problem I was having. My house batteries are a bank of forklift batteries that give me a total of 650amp. I am currently moored and am connected to mains power which provides power and charges batteries. I run two separate systems in the boat - 240v for when I am on shore power or generator and the 24v system which is always on. When cruising, I have a separate alternator on the engine to charge the house batteries.

Something else occurred to me. I said before that I am running similar equipment on the same loop but that might not be true. The 24v outlet I am using is actually wired into the electrics for a crane. It is possible ( and now I think likely) that this particular outlet is not in the 24v outlet loop but is just tapped into a convenience source. I'm not sure if that changes anything.

Thanks for all of the advice so far. It has been very enlightening.
 
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Old 07-14-17, 01:19 AM
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A separate alternator for the house batteries keeps them completely isolated from the starting batteries. That means starting the engine is not your problem unless the starting control circuitry comes off the house batteries.

Electronic devices like motors and solenoids can create large EMF spikes when they are turned off. They are similar at that point to an ignition coil which generates high voltage when it's turned off.

Those spikes are well over the operating voltage of the system and are very likely what is causing your problem. You should have dedicated wiring directly to the house batteries for sensitive electronics. A device like a crane could release a large spike.

The battery bank acts like a big filter and will reduce those spikes traveling thru the battery if the circuits are separate.
 
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Old 07-14-17, 01:55 AM
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And something else has just occurred to me! I have a switch that allows me to parallel the house and engine batteries. Because the engine battery is not being charged when I am on mains power it is often too flat to start the engine. Thus I have being switching to parallel to get the engine started. This would then bring the house batteries into the starter circuit?
 
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Old 07-14-17, 09:35 AM
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Thus I have being switching to parallel to get the engine started. This would then bring the house batteries into the starter circuit?
Yes, definately a source for transients. Is this a single engine boat? Slightly more work, but single engine boats can use two starting batteries with a smart isolator/charging relay between them and also use the emergency parallel switch/relay. In a twin, simply run the contactor between each starting battery.
As you finding out, running electronics with a large starter motor in the circuit is not good. Your "crane"/davit will also supply some transient, but should be much less than a diesel starter.


So, your easiest option is to put in a noise filter/transient filter to just the electronic loads; Better is a second start battery to always keep the house battery out of the circuit. Best is to do both.
 
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Old 07-14-17, 10:12 AM
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You could also install a charger for the starting battery to charge when docked.
 
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Old 07-14-17, 10:39 AM
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Texas Instruments designs IC's including one for the electronic tail light controller on 12V cars. Their design criteria calls for withstand of +100 and -300 Volt transients on the 12V line! The protection circuitry is shockingly complex.


http://www.ti.com/lit/an/snva717/snva717.pdf
 
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Old 07-17-17, 06:50 AM
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Thanks to everyone who contributed their expertise to this problem. I have learned a lot in the last week.

My final question is:- Is there a way that I can test to see if the engine start is causing the problem? A small multimeter is the limit of my technology.

Cheers

Stevw
 
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Old 07-17-17, 09:56 AM
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SCR Principles And Circuits - Nuts & Volts Magazine - For The Electronics Hobbyist

If I had no test equipment, I would build up figure 5. Instead of R1, I'd use various Zeners, like maybe a 50V. So, if you sustain a transient of over 50 volts, the alarm /light would energize.

PS: these are what I used on my last boat. Just after the fuse/breaker, before the electronic device. SLD28U-017 (for 24V systems)

http://www.littelfuse.com/~/media/el...asheet.pdf.pdf
 

Last edited by telecom guy; 07-17-17 at 10:21 AM.
 

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