A Look at Voltage Transients In a Marine Battery System
I had been meaning to put this together for a while and assembled a system for a training class I was doing. Once that was assembled I realized I could simply add a starter motor, an oscilloscope and a Fluke 289 & Fluke 376 and then would would was able to create a video on voltage transients.
In the video I’m walking through the very typical, though not necessarily ideal, marine battery system which utilizes the venerable 1, BOTH, 2, OFF battery switch. The typical 1, BOTH, 2, OFF switch is configured for both bank charge selection and bank use selection.
With this switch configuration the battery bank selected, via the switch, serves as both a house and starting bank as well as the bank which gets charged.
Here's the video (Warning: It's 16 minutes):
“You Must Have a Dedicated Starting Battery”
This gets repeated over and over on docks in magazines and on the web, and there is a bit of good intention in it but also some myth. While a dedicated starting battery is never a bad idea it is also not a 100% solution to eliminating transients in a marine system. So what is a dedicated start battery?
Dedicated Starting Battery: A battery used and wired as such that its only purpose is for starting the motor and powering engine electronics. It will have its own isolation switch though may often have the ability for a paralleled connection to the house bank, if needed in an emergency. A dedicated starting battery isolates starting from house loads.
Unfortunately starter motors are just one example of devices that can create a voltage transient. As can be seen in the video where you connect your DC panel loads matters and can greatly minimize the potential for transients.
Potential Damaging Sources – Other Than Starter Motor:
Despite all the above potential sources of transients in well wired boats I rarely measure transients above 14V – 15V but when boats have been wired haphazardly I can measure transients in excess of 25V+.
It's important to recognize that the act of using a dedicated starting battery does not absolve your house bank of the risk of voltage transients. Starter motors are not the only potential source of transients.
Spending the money on a dedicated starting battery, despite all the marketing efforts by battery switch makers etc, will not remove all the potential for transients from your marine house bank but it can remove one potential.
Bottom Line:
Keep your DC load positive & negative take off points as close to the battery bank as possible and this includes keeping your battery switch as close to the batteries as possible. Best practice is to use only use one take off point for DC electronic loads, as close to the bank as possible, and you can minimize the potential for transients. If you are really concerned about this it can be measured and tested for using the proper equipment..
There are also tricks such as TVS diodes and devices to help eliminate and or minimize the risk further but generally, in a well wired system, this is not something you need to be hugely concerned with.
I had been meaning to put this together for a while and assembled a system for a training class I was doing. Once that was assembled I realized I could simply add a starter motor, an oscilloscope and a Fluke 289 & Fluke 376 and then would would was able to create a video on voltage transients.
In the video I’m walking through the very typical, though not necessarily ideal, marine battery system which utilizes the venerable 1, BOTH, 2, OFF battery switch. The typical 1, BOTH, 2, OFF switch is configured for both bank charge selection and bank use selection.
With this switch configuration the battery bank selected, via the switch, serves as both a house and starting bank as well as the bank which gets charged.
Here's the video (Warning: It's 16 minutes):
“You Must Have a Dedicated Starting Battery”
This gets repeated over and over on docks in magazines and on the web, and there is a bit of good intention in it but also some myth. While a dedicated starting battery is never a bad idea it is also not a 100% solution to eliminating transients in a marine system. So what is a dedicated start battery?
Dedicated Starting Battery: A battery used and wired as such that its only purpose is for starting the motor and powering engine electronics. It will have its own isolation switch though may often have the ability for a paralleled connection to the house bank, if needed in an emergency. A dedicated starting battery isolates starting from house loads.
Unfortunately starter motors are just one example of devices that can create a voltage transient. As can be seen in the video where you connect your DC panel loads matters and can greatly minimize the potential for transients.
Potential Damaging Sources – Other Than Starter Motor:
- Windlass
- Bow Thruster
- Electric Winches
- Electric Windshield Wipers (power boats mostly)
- Engine Driven Refrigeration Clutch
- DC Motors (these transients can occur on the negative side too)
- DC Refrigeration
- Water Makers
- A Load Dump of an Alternator (passing a switch through OFF)
- Inverters
- Water Makers
- Electric heads
- Water & Washdown Pumps
- SSB Radio
- Bilge Blower
- Battery Charger
- Battery Switch
- Relays, Solenoids & Combiners
- 12V Appliances – Blenders etc.
- Electric Oil Pumps
- Bilge Pumps
- Etc. etc..
Despite all the above potential sources of transients in well wired boats I rarely measure transients above 14V – 15V but when boats have been wired haphazardly I can measure transients in excess of 25V+.
It's important to recognize that the act of using a dedicated starting battery does not absolve your house bank of the risk of voltage transients. Starter motors are not the only potential source of transients.
Spending the money on a dedicated starting battery, despite all the marketing efforts by battery switch makers etc, will not remove all the potential for transients from your marine house bank but it can remove one potential.
Bottom Line:
Keep your DC load positive & negative take off points as close to the battery bank as possible and this includes keeping your battery switch as close to the batteries as possible. Best practice is to use only use one take off point for DC electronic loads, as close to the bank as possible, and you can minimize the potential for transients. If you are really concerned about this it can be measured and tested for using the proper equipment..
There are also tricks such as TVS diodes and devices to help eliminate and or minimize the risk further but generally, in a well wired system, this is not something you need to be hugely concerned with.