Hi Jeff, I have questions about electrical relays on my new sail boat. The manual lists 3 relays: 1. Bilge pump 2. Windless 3. Bow thruster So my questions are: 1. What does a relay do? 2. How do I know the relay is working? 3. What maintenance is necessary for a relay? Thanks for your help and I very much enjoy your videos. Marshall
Two types of relays...mechanical and electronic. Relays allow you to control (turn on or off) large voltage/current with a small voltage/current. Consider starting circuit...starter motor needs huge current and large cables. Relay contacts (normally open) would be connected, with large cables, between battery and starter; when that contact closes, large current flows to the motor. To activate the relay a small (low current) wire would run from battery supply bus to a smallish starter switch at the dash and then to the activating coil on relay. When starter switch is closed, a current flows through relay coil that creates magnetic field pulling the open contact closed and allowing large current to flow through contact to starter motor. An electronic relay does same thing, but no moving parts...just transistors. Typically there is no maintenance you can do on relay bec they are a sealed unit.
I think you mentioned before disconnecting shore power we should turn off all a/c circuits at the panel, then turn off the main circuit, then unplug. I always turn off main circuit before unplugging, but I haven't turn off each individual circuit first. Should I? What is happening when I don't?
If you shut off main breaker, it needs to interrupt all the current. If you shut of the individual breakers first, each smaller breaker interrupts much less current and then main breaker has less current (maybe none) to interrupt...kinda like jumping off a cliff (ie opening the main breaker under load) vs taking steps down the cliff (ie opening individual breakers).
Excellent discussion, Jeff. Please correct me if I'm wrong, but in both AC and DC power scenarios, sparking damage to connectors and equipment can occur. In DC however, current is flowing one way only, and at high volts and amps, the arc produced can be very long lasting, very hot and damaging. I have been using a large DC circuit breaker to disconnect the panels, but now appreciate that solar cell damage can occur. Thanks again for your clarifications.
Disconnecting circuit under load will create an arc...the air between contacts as contact opens gets ionised and allows current to flow (that is the arc you see). With an AC circuit, the voltage is constantly changing from maximum in one direction to maximum in opposite direction...when the voltage passes through zero, the arc stops, the ionised gas dissipates sufficiently that the arc does not reestablish. With DC, the voltage never drops to zero so the arc continues. Breakers and fuses have two primary ratings: a trip/blow rating and a maximum interrupt rating...when selecting a fuse/breaker you need to consider the maximum current the wiring can handle (trip/blow rating) and the maximum current the supply can produce (maximum interrupt rating). If you have a wire that can handle 10A, you could add a 12A or 15A fuse/breaker. If the supply, a large battery, can produce 700A (ie cold cranking amps) your fuse/breaker must be able to interrupt that amount of current. Extinguishing the arc on DC circuit is much more difficult which is why fuses and breakers have an AC rating and a DC rating for maximum interrupt capability; the AC max interrupt rating is much higher than the DC interrupt rating.
I should also add, there is always a spark when opening a breaker or switch when circuit is operating...that small arc is beneficial in keeping the contact clean. The arc helping keep the contacts clean is why oversizing a contactor (aka power relay) is bad...not as bad as undersizing, but you would not want a 100A contactor/relay on a 1A circuit because the arc from 1A is not enough to burn off any oxides that form on the contact surfaces.
You didn’t really answer the question. Every circuit has inductance. When current is flowing through inductance it creates a magnetic field, sudden interruption of the current (pulling vacuum cleaner plug out of the wall or disconnecting solar panel) manifests as a voltage spike due to collapsing magnetic field in the inductive elements. The magnitude of the voltage spike is affected by the amount of inductance and the amount of current flowing when the circuit is broken (2, 3, 5 even 10 times rated voltage for an instant). The voltage spike is measured at the solar panel terminals and although the spike is very short duration it is that voltage spike that will punch through the insulation between +ve and -ve parts of the solar cell. If the insulation in cell(s) gets damaged, the cell(s) no longer produce power. The cells closest the the terminals are the ones that will see the biggest voltage spike and most likely the ones that get damaged. Covering panel(s) with blanket is a good idea, but adding a make-before-break disconnect switch that connects a high value resistor across the solar panel terminals is good insurance against any possible voltage spikes.
you can also install limited surge protection on both DC and AC circuit as a backup if you are qualified electrical trade person or for AC you can buy one that just plug into the AC wall plug. I still do not know whether these approaches will help with an EMF burst from nearby lightning strike, any thoughts on this would be well appreciated
@@PacificYachtSystems sorry I am a electrical engineer retired so i have plenty of time to look at these type of things. I still do not know whether this will help in a lightning surge situation Available in 24V DC surge protection brand BEP module part No. 80-707-0005-00 www.marine-deals.com.au/meters-and-monitors/bep-surge-protection-module PRODUCT DESCRIPTION: The Surge Protector will protect against transient pulses and surges from electrical/ electronic devices such as motors and pumps. It also protects against high energy surges such as an alternator load dump from a battery cable removal while under high charge currents. Designed to meet ISO 7637 -1 (12V), ISO 7637 -2 & SAEJ1113-11. There are versions for 12- & 24-volt systems. The Surge Protector essentially ‘Clamps’ the voltage at 17V (12V system) or 35V (24V system) The module is polarity sensitive and must be wired correctly to operate. It should be wired as near to the load as is practicable ie, after long cable runs & battery isolators etc. There is a 250mA relay output (at battery voltage) that is that latches on under high energy surges of >1-2ms and can be used to drive an LED indicator. The relay will latch when activated and will only reset after power is removed and reapplied. The relay will not become active under transient pulses as they can occur frequently. For AC protection can get surge protection at the local electrical wholesaler au.rs-online.com/web/c/passive-components/surge-protection-components/surge-suppressor-units/ also socket mounts eg. Belkin 6-Outlet USB Surge Protector, Wall Mount - Ideal for Mobile Devices, Personal Electronics, Small Appliances and More (900 Joules) EMP burst can happen when lightning strike near an water areas and can take out the electrical systems on board boats if not protected some people install these Fore spar Lightning Master Static Dissipater Rod www.amazon.com/Forespar-Lightning-Master-Static-Dissipater/dp/B000XBDFJO/ref=sr_1_1?dchild=1&keywords=lightning+master+static+dissipater+rod&qid=1606727675&sr=8-1 • Lowers the likelihood of a direct lightning strike by reducing the build-up of static ground charge and retarding the formation of ion streamers • Lightweight 21" long dissipater mounts to the masthead and extends vertically above all other masthead equipment. • Fore spar does not claim that this product is 100% effective in preventing a lightning strike. This product does, however, control the known causes of lightning strikes and thereby reduces the incidence of direct strikes. but do not know whether this is like elephant repellent which you do know if it works unless an elephant turns up hope this helps
Thanks for this. Question: doesn't flipping a switch or breaker make that same non-immediate interruption? Wouldn't the contacts in the switch/breaker get tarnished and scortched?
@@PacificYachtSystems thanks for the answer. But I’m referring about how to protect pv panels if there aren’t diodes installed, are fuses right to do the job?
Hi Jeff,
I have questions about electrical relays on my new sail boat. The manual lists 3 relays:
1. Bilge pump
2. Windless
3. Bow thruster
So my questions are:
1. What does a relay do?
2. How do I know the relay is working?
3. What maintenance is necessary for a relay?
Thanks for your help and I very much enjoy your videos.
Marshall
Two types of relays...mechanical and electronic. Relays allow you to control (turn on or off) large voltage/current with a small voltage/current. Consider starting circuit...starter motor needs huge current and large cables. Relay contacts (normally open) would be connected, with large cables, between battery and starter; when that contact closes, large current flows to the motor. To activate the relay a small (low current) wire would run from battery supply bus to a smallish starter switch at the dash and then to the activating coil on relay. When starter switch is closed, a current flows through relay coil that creates magnetic field pulling the open contact closed and allowing large current to flow through contact to starter motor. An electronic relay does same thing, but no moving parts...just transistors.
Typically there is no maintenance you can do on relay bec they are a sealed unit.
@@borysnijinski331 Thank you. Clearer
Thanks Borys!
I think you mentioned before disconnecting shore power we should turn off all a/c circuits at the panel, then turn off the main circuit, then unplug. I always turn off main circuit before unplugging, but I haven't turn off each individual circuit first. Should I? What is happening when I don't?
If you shut off main breaker, it needs to interrupt all the current. If you shut of the individual breakers first, each smaller breaker interrupts much less current and then main breaker has less current (maybe none) to interrupt...kinda like jumping off a cliff (ie opening the main breaker under load) vs taking steps down the cliff (ie opening individual breakers).
Very well said Borys, thanks for sharing.
Excellent discussion, Jeff. Please correct me if I'm wrong, but in both AC and DC power scenarios, sparking damage to connectors and equipment can occur. In DC however, current is flowing one way only, and at high volts and amps, the arc produced can be very long lasting, very hot and damaging. I have been using a large DC circuit breaker to disconnect the panels, but now appreciate that solar cell damage can occur. Thanks again for your clarifications.
Disconnecting circuit under load will create an arc...the air between contacts as contact opens gets ionised and allows current to flow (that is the arc you see). With an AC circuit, the voltage is constantly changing from maximum in one direction to maximum in opposite direction...when the voltage passes through zero, the arc stops, the ionised gas dissipates sufficiently that the arc does not reestablish. With DC, the voltage never drops to zero so the arc continues. Breakers and fuses have two primary ratings: a trip/blow rating and a maximum interrupt rating...when selecting a fuse/breaker you need to consider the maximum current the wiring can handle (trip/blow rating) and the maximum current the supply can produce (maximum interrupt rating). If you have a wire that can handle 10A, you could add a 12A or 15A fuse/breaker. If the supply, a large battery, can produce 700A (ie cold cranking amps) your fuse/breaker must be able to interrupt that amount of current. Extinguishing the arc on DC circuit is much more difficult which is why fuses and breakers have an AC rating and a DC rating for maximum interrupt capability; the AC max interrupt rating is much higher than the DC interrupt rating.
I should also add, there is always a spark when opening a breaker or switch when circuit is operating...that small arc is beneficial in keeping the contact clean. The arc helping keep the contacts clean is why oversizing a contactor (aka power relay) is bad...not as bad as undersizing, but you would not want a 100A contactor/relay on a 1A circuit because the arc from 1A is not enough to burn off any oxides that form on the contact surfaces.
@@borysnijinski331 thanks so much for weighing in on this. The subtleties of electricity are so interestingly exquisite......curiosity strikes again!
@@henriaube2278 30 yrs as an electrical engineer and still learning.
Just gold, so well explained.
You didn’t really answer the question. Every circuit has inductance. When current is flowing through inductance it creates a magnetic field, sudden interruption of the current (pulling vacuum cleaner plug out of the wall or disconnecting solar panel) manifests as a voltage spike due to collapsing magnetic field in the inductive elements. The magnitude of the voltage spike is affected by the amount of inductance and the amount of current flowing when the circuit is broken (2, 3, 5 even 10 times rated voltage for an instant). The voltage spike is measured at the solar panel terminals and although the spike is very short duration it is that voltage spike that will punch through the insulation between +ve and -ve parts of the solar cell. If the insulation in cell(s) gets damaged, the cell(s) no longer produce power. The cells closest the the terminals are the ones that will see the biggest voltage spike and most likely the ones that get damaged. Covering panel(s) with blanket is a good idea, but adding a make-before-break disconnect switch that connects a high value resistor across the solar panel terminals is good insurance against any possible voltage spikes.
You explained it well, but to Jeff's target audience I bet this is gobbledygook.
Good one, thanks for sharing!
Very good info, ty for sharing Jeff.
Any time!
you can also install limited surge protection on both DC and AC circuit as a backup if you are qualified electrical trade person or for AC you can buy one that just plug into the AC wall plug.
I still do not know whether these approaches will help with an EMF burst from nearby lightning strike, any thoughts on this would be well appreciated
Hi David, can you tell me more about this. Not sure i understand what you mean?
@@PacificYachtSystems sorry I am a electrical engineer retired so i have plenty of time to look at these type of things. I still do not know whether this will help in a lightning surge situation
Available in 24V DC surge protection brand BEP module part No. 80-707-0005-00
www.marine-deals.com.au/meters-and-monitors/bep-surge-protection-module
PRODUCT DESCRIPTION:
The Surge Protector will protect against transient pulses and surges from electrical/ electronic devices such as motors and pumps. It also protects against high energy surges such as an alternator load dump from a battery cable removal while under high charge currents. Designed to meet ISO 7637 -1 (12V), ISO 7637 -2 & SAEJ1113-11. There are versions for 12- & 24-volt systems.
The Surge Protector essentially ‘Clamps’ the voltage at 17V (12V system) or 35V (24V system) The module is polarity sensitive and must be wired correctly to operate. It should be wired as near to the load as is practicable ie, after long cable runs & battery isolators etc. There is a 250mA relay output (at battery voltage) that is that latches on under high energy surges of >1-2ms and can be used to drive an LED indicator. The relay will latch when activated and will only reset after power is removed and reapplied. The relay will not become active under transient pulses as they can occur frequently.
For AC protection can get surge protection at the local electrical wholesaler
au.rs-online.com/web/c/passive-components/surge-protection-components/surge-suppressor-units/
also socket mounts eg. Belkin 6-Outlet USB Surge Protector, Wall Mount - Ideal for Mobile Devices, Personal Electronics, Small Appliances and More (900 Joules)
EMP burst can happen when lightning strike
near an water areas and can take out the electrical systems on board boats if not protected
some people install these Fore spar Lightning Master Static Dissipater Rod
www.amazon.com/Forespar-Lightning-Master-Static-Dissipater/dp/B000XBDFJO/ref=sr_1_1?dchild=1&keywords=lightning+master+static+dissipater+rod&qid=1606727675&sr=8-1
• Lowers the likelihood of a direct lightning strike by reducing the build-up of static ground charge and retarding the formation of ion streamers
• Lightweight 21" long dissipater mounts to the masthead and extends vertically above all other masthead equipment.
• Fore spar does not claim that this product is 100% effective in preventing a lightning strike. This product does, however, control the known causes of lightning strikes and thereby reduces the incidence of direct strikes.
but do not know whether this is like elephant repellent which you do know if it works unless an elephant turns up
hope this helps
Thanks for this. Question: doesn't flipping a switch or breaker make that same non-immediate interruption? Wouldn't the contacts in the switch/breaker get tarnished and scortched?
Switches and breakers are designed to deal with the arc...the arc is actually important in keeping the contacts clean by burning off oxides.
Good one Borys.
Hello, should we cover the solar panels even if we use a bipolar switch to disconnect them from the batteries?
Good question, out of abundance caution, I'd say yes.
What about how protecting pv panels from reverse current when there is more then one string installed, fuses should not be used?
Sounds like you are referring to diodes, and many panels have them built-in as a part of the junction box.
@@PacificYachtSystems thanks for the answer. But I’m referring about how to protect pv panels if there aren’t diodes installed, are fuses right to do the job?
Now for disconnecting solar panels, should we disconnect the + line first, so any excess current has somewhere to go (through the -)?
Hi Ben, don't think it would matter as any disconnect in the circuit will work. Perhaps someone more knowledgeable can answer this question.
💯
Thanks Javier!