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Dual Lightspeed igntion install - warning

Carl Froehlich

Well Known Member
I'm helping an RV owner complete a conditional inspection. He has dual six cylinder Lightspeed ignitions installed.

As I'm guessing with most Lightspeed installs, he has a standard electrical (one battery, one alternator) system, with the added dedicated backup aux battery for the Lightspeed igntion exactly as Klaus depicts in his instructions.

While the install does have a selector switch to monitor main or aux battery voltage, it does not allow for measuring aux battery voltage with the main battery out of the system. As a result, the aux voltage reading is either the aux battery itself, or the voltage from the diode isolated feed from the main power system. As such, unless the main battery has been disconnected, the aux voltage reading does not detect a failed aux battery.

I did a simple check of the aux battery by measureing voltage across the battery terminals with the master switch off. The battery showed 2.3 vdc. In short, this batttery has been little more than a brick for a long time, and if the main battery system failed the engine would have stopped.

Lesson learned. If you are flying around with a Lightspeed install and using Klaus' backup power design, spend the $20 and replace the backup batttery every year. If you are not flying with Lightpseed and are considering installing an electronic igntion, consider pMag. If you must fly with Lightspeed, there are far better, two battery power distribution schemes you should consider.

Carl
 
Harbor Freight

HF is always giving away free volt meters. I must have a dozen now. In each car, travel trailer, boat etc. It is a simple matter to always check resting voltages in our batteries. Especially if life depends on it.
 
I did a simple check of the aux battery by measuring voltage across the battery terminals with the master switch off. The battery showed 2.3 vdc. In short, this battery has been little more than a brick for a long time, and if the main battery system failed the engine would have stopped.

I have bench tested a Powersonic backup battery for over five years now..... with a full charge the battery would drop from 12.8 volts to 12.4 volts in a 12 month period. Lightspeed will operate down to 5.5 volts.

I would consider this battery as a safe backup for Lightspeed ignition, and check the voltage only 4 times a year or any time I want to.

The battery that you found as a backup was not a good backup or it was installed and ignored.
 
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While the install does have a selector switch to monitor main or aux battery voltage, it does not allow for measuring aux battery voltage with the main battery out of the system. As a result, the aux voltage reading is either the aux battery itself, or the voltage from the diode isolated feed from the main power system. As such, unless the main battery has been disconnected, the aux voltage reading does not detect a failed aux battery.

Carl

Hi Carl,

Looking at the Lightspeed diagram I'm not quite sure I understand the problem. It would appear that you can in fact check the Aux battery voltage independently, by simply pulling the breaker that is in line with the diode.
 
Hi Carl,

Looking at the Lightspeed diagram I'm not quite sure I understand the problem. It would appear that you can in fact check the Aux battery voltage independently, by simply pulling the breaker that is in line with the diode.

Even includes a voltmeter in the diagram.

Given that EI and EFI are becoming more common, perhaps it's time for our EAB EFIS suppliers to provide two separate voltage monitor inputs with alarms. My faithful GRT Sport SX only has one, thus a requirement for a stand-alone monitor on the second power source (like the Lightspeed drawing). There are boatloads of cheap panel voltmeters available, but I really didn't want an extra light in the cockpit at night.
 
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Small panel mount dual voltmeters are a few bucks on fleeb. I monitor dual batteries with my MGL and VPX. These give alarms for both, too. It's an exceptional idea to monitor a critical power source.
 
Hi Carl,

Looking at the Lightspeed diagram I'm not quite sure I understand the problem. It would appear that you can in fact check the Aux battery voltage independently, by simply pulling the breaker that is in line with the diode.

Yep, a lot of ways to do this better - but I did not build this plane, I'm just a helper.

As I have posted in the past, there are much better ways to achieving a robust electrical power distribution scheme other than the use of backup batteries for igntions, EFIS or whatever. If I ever did install a Lightspeed ignition (which I never would), I would not use the Klaus backup battery design.

Carl
 
Even includes a voltmeter in the diagram.

Given that EI and EFI are becoming more common, perhaps it's time for our EAB EFIS suppliers to provide two separate voltage monitor inputs with alarms. My faithful GRT Sport SX only has one, thus a requirement for a stand-alone monitor on the second power source (like the Lightspeed drawing). There are boatloads of cheap panel voltmeters available, but I really didn't want an extra light in the cockpit at night.

AFS (Advanced Flight Systems) provides this as well. My 5600Ts display battery voltage and alternator amperage simultaneously on both of my electrical systems. Alarm conditions are configurable for each.
 
Tell us why.

I posted on this in the past. Short story:
- Three RV-8/8As building at the about the same time. Each going with dual Lightspeed ignitions.
- All six ignitions arrived with bad (as in cold solder joints) connectors. I called Klaus and he told me I was wrong. I sent them back - his only comment was "they look bad".
- All six ignitions had a main board problem. I called Klaus and again he told me I was wrong and/or I installed them wrong. I sent on box back and Klaus found a 100K ohm resistor where a 100 ohm resistor should have been (I could be wrong on the specific numbers). Klaus fixed the one box I sent back and sent me five correct resistors for me to do a field repair of his boxes. He never even paid for my shipping cost, or a thank you for the field repair on my time or for finding a his production error.
- One RV got sold in Brazil so I don't know what issues they may or may not have experienced.
- The other two RVs had 3 out of 4 boxes with multiple hard failures in the first 300 hours.

At that point I deemed the ignition non-airworthy and replaced with dual pMags (650+ trouble free hours).

I'm just summing up my experience and I'm sure many have never had a problem with Lightspeed - so I don't need any flames.

Carl
 
I posted on this in the past. Short story:

Not the ignitions. Tell us why you "would not use the Klaus backup battery design". The design, referenced by Alan with a link, is capable of operating any of the available EI's.[
 
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Not the ignitions. Tell us why you "would not use the Klaus backup battery design". The design, referenced by Alan with a link, is capable of operating any of the available EI's.

Ok - got it.

If a builder wants the simple single battery, single alternator 1960 Cessna power distribution design - and wants to add a Lightspeed ignition, then adding a dedicated backup battery does meet that need, but only that one need.

But most builders these days add backup batteries for each EFIS display and other stuff. So an airplane can soon have a lot of backup batteries that spend most of their lives as dead weight, needing tending and periodic replacement.

If a builder steps back and looks at the overall system design objectives, I offer that a single alternator and two main batteries design will fulfill functions of the backup batteries as well as provide a much higher level of redundancy. My preference is two PC-625 batteries (I have posted on this in the past).

Three RV-8/8As and one RV-10 flying with this design - it has proven its value.

Carl
 
I hear you on carrying around a lot of backup batteries, but i am also a believer that the backup battery for the ignition system in a dual electronic ignition system should ONLY be wired to the ignitions. It should be tested regularly under flight conditions. I would not want to have to shut down the electrical system in an aircraft due to a short or an electrical fire and have to deal with an engine outage at the same time.

Vic
 
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...I offer that a single alternator and two main batteries design will fulfill functions of the backup batteries as well as provide a much higher level of redundancy.

Got a sketch or diagram? Don't need the whole aircraft, just ignition power distribution.
 
I hear you on carrying around a lot of backup batteries, but i am also a believer that the backup battery for the ignition system in a dual electronic ignition system should ONLY be wired to the ignitions. It should be tested regularly under flight conditions. I would not want to have to shut down the electrical system in an aircraft due to a short or an electrical fire and have to deal with an engine outage at the same time.

Vic

Yep - I agree and cover such an issue (and other faults) in the design.

Carl
 
I'll send you the details, but just doing this for ignition backup is a waste.

Well, gosh, we are talking about "Dual Lightspeed install", per your thread title and first post, which BTW, seems to burn Lightspeed for an installation which does not match Lightspeed drawings. As drawn (and as noted by Alan), simply pulling the breaker allows looking at IGN2 battery voltage, at any time. When installed per drawing, there is no reason to be flying with a dead ignition battery.

I think we would like to see why your two batteries and one alternator is better than Lightspeed's two batteries and one alternator. After all, details do matter. Please post your diagram.

There are other ways to provide battery monitoring. Here's a little add-on circuit...one relay, one momentary SPST switch, and a $3 two-wire digital voltmeter display. Pushing the button disconnects BATT2 from charging, and connects to the voltmeter. The VM display, normally dark, lights up and shows BATT2 voltage under ignition load, in flight or any time. Don't even need the master on.



I already have a monitor to alert if BATT2 becomes disconnected from charging, so I think I'll add the above test circuit. Pushing the button will even check the monitor.

http://www.vansairforce.com/community/showpost.php?p=1159312&postcount=166
 
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I posted on this in the past. Short story:

Not the ignitions. Tell us why you "would not use the Klaus backup battery design". The design, referenced by Alan with a link, is capable of operating any of the available EI's.

Returning to the Lightspeed design, lemme help you out....specific design details, not philosophy. Maybe you can add another.

Why Dan doesn't use the Lightspeed ignition power distribution, as drawn (http://lightspeed-aero.com/Manuals/PS_Diagram.htm):

1. The power source select switch for IGN2 is potentially risky, and unnecessary. In regular operation, it would be foolish to regularly connect both ignitions to the same power source, as source failure would require a pilot action (switching to BATT2) to resume engine power. We don't always have time to identify the reason for silence and take the correct action. Better to always have IGN2 hooked to BATT2.

2. Using a breaker in the BATT2 feed line requires running an unprotected hot lead from the battery to the instrument panel, not a good thing with a front battery and definitely not good with rear batteries. The hot lead should be protected at the battery positive, which makes the breaker redundant. A switch would serve just as well for the test function.
 
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Returning to the Lightspeed design, lemme help you out....specific design details, not philosophy. Maybe you can add another.

Why Dan doesn't use the Lightspeed ignition power distribution, as drawn:

1. The power source select switch for IGN2 is potentially risky, and unnecessary. In regular operation, it would be foolish to regularly connect both ignitions to the same power source, as source failure would require a pilot action (switching to BATT2) to resume engine power. We don't always have time to identify the reason for silence and take the correct action. Better to always have IGN2 hooked to BATT2.

2. Using a breaker in the BATT2 feed line requires running an unprotected hot lead from the battery to the instrument panel, not a good thing with a front battery and definitely not good with rear batteries. The hot lead should be protected at the battery positive, which makes the breaker redundant. A switch would serve just as well for the test function.
So a question on this topic. Could one not cross feed power from each battery to each EI? Battery 1 has a feed to EI-1 and EI-2. Battery 2 also has a feed to EI-1 and EI-2. Include diodes inline from each cross feed battery to prevent current draw from one battery draining the other battery. It seems to me this would be a good redundant configuration.

Anything amiss with this idea?
 
Well, gosh, we are talking about "Dual Lightspeed install", per your thread title and first post, which BTW, seems to burn Lightspeed for an installation which does not match Lightspeed drawings....SNIP...

Dan,

Yep - as I said before not my install - I'm just a helper on this plane. The whole point of my original post is if I found this problem on an RV I suspect it exists elsewhere - so my warning for people to check what they have.

I sent you a long email on the two PC-625 battery design. This includes the original design for the three RV-8/8As that was based on supporting dual Lightspeed installs. While the follow on projects do not use Lightspeed ignitions, the redundancy and simplicity of a design based on two PC-625s has provided good service in the RV-10. The same design will go into the new RV-8 project.

So to boil all this down - if you take the step of adding a backup battery for your ignition, look at what other doors this opens to achieving your design objectives for redundant power distribution.

Carl
 
Well, gosh, we are talking about "Dual Lightspeed install", per your thread title and first post, which BTW, seems to burn Lightspeed for an installation which does not match Lightspeed drawings. As drawn (and as noted by Alan), simply pulling the breaker allows looking at IGN2 battery voltage, at any time. When installed per drawing, there is no reason to be flying with a dead ignition battery.

I think we would like to see why your two batteries and one alternator is better than Lightspeed's two batteries and one alternator. After all, details do matter. Please post your diagram.

There are other ways to provide battery monitoring. Here's a little add-on circuit...one relay, one momentary SPST switch, and a $3 two-wire digital voltmeter display. Pushing the button disconnects BATT2 from charging, and connects to the voltmeter. The VM display, normally dark, lights up and shows BATT2 voltage under ignition load, in flight or any time. Don't even need the master on.



I already have a monitor to alert if BATT2 becomes disconnected from charging, so I think I'll add the above test circuit. Pushing the button will even check the monitor.

http://www.vansairforce.com/community/showpost.php?p=1159312&postcount=166

Dan, I like the disconnect to check voltage concept. Why not a simple spdt momentary one direction switch instead of the relay?
 
Dan, I like the disconnect to check voltage concept. Why not a simple spdt momentary one direction switch instead of the relay?

Glad you asked. I have rear batteries. Even with front batteries, I don't want to run a hot lead from the main contactor to a panel location, and then to BATT2. By using a relay, the hot lead can be short and robust, not passing through the airframe. The wires to the panel are non-critical:

An open wire to the switch merely renders the self test inoperative.

A shorted wire to the switch lights the voltmeter and halts charging, but the ignition doesn't fail.

An open wire to the voltmeter merely renders it inoperative.

A shorted wire to the voltmeter blows the fusible link when the test function is operated, which halts charging, but again, the ignition remains operative.
 
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Glad you asked. I have rear batteries. Even with front batteries, I don't want to run a hot lead from the main contactor to a panel location, and then to BATT2. By using a relay, the hot lead can be short and robust, not passing through the airframe. The wires to the panel are non-critical:

An open wire to the switch merely renders the self test inoperative.

A shorted wire to the switch lights the voltmeter and halts charging, but the ignition doesn't fail.

An open wire to the voltmeter merely renders it inoperative.

A shorted wire to the voltmeter blows the fusible link when the test function is operated, which halts charging, but again, the ignition remains operative.

Understood, and makes sense. And, if the relay should fail to close (NC I assume!), you'll see it in the ongoing voltage monitoring.

What is the switch just to the right of "EI"? Seems you must have juice going by the panel anyway on its way to the ignition?
 
What is the switch just to the right of "EI"? Seems you must have juice going by the panel anyway on its way to the ignition?

Yes, power switch ("mag switch") for each ignition. No choice; gotta carry power from the back to the front. Those long runs are protected with a fusible link at the source.
 
Diode

I did a simple check of the aux battery by measureing voltage across the battery terminals with the master switch off. The battery showed 2.3 vdc. In short, this batttery has been little more than a brick for a long time, and if the main battery system failed the engine would have stopped.

I have been noodling a dedicated aux battery design for my dual elec ignition and I really like Dan's approach. I still wonder/worry why there are reports from time to time of dead aux batteries with Klaus' schematic.

I'd like to assume that the issues are directly related to neglect of the aux battery for multiple years, but I can't help but wonder if the diode in the charging circuit is possibly accelerating the life of the small aux battery. (by not allowing it to live/charge at full alternator voltage)

Have those who fly with this design had good luck with aux battery life? Do you generally test & replace them annually?

Thanks in advance,
Rob
 
I still wonder/worry why there are reports from time to time of dead aux batteries with Klaus' schematic.

I'd like to assume that the issues are directly related to neglect of the aux battery for multiple years, but I can't help but wonder if the diode in the charging circuit is possibly accelerating the life of the small aux battery. (by not allowing it to live/charge at full alternator voltage)

Good subject.

Theory says the application is an uninterruptible power supply; the 1 amp to operate IGN2 is coming from the alternator, not BATT2. The battery is just sitting there fully charged. Odyssey (for example) specs 13.6 as the float voltage. I assume all the AGM batteries are similar. Currently I'm using a Motobatt MB3U, as Odyssey doesn't make a battery in this size.

http://www.motobatt.com/download_pdf.php?p=103

One approach to the question might be to load test this battery after flying it a few months, just to see it actual state of charge.
 
Float Charge

One approach to the question might be to load test this battery after flying it a few months, just to see it actual state of charge.

I agree that that the battery won't theoretically see any load during normal flight ops, but it will self-discharge a bit in between flights and will be in use while starting the engine. So is the 13.9V downstream of the schottky diode high enough to restore that energy?

I think close monitor of the battery's condition/behavior for your particular system is the right answer. Since my plane is still a project, I'm thinking of hooking my aux batt up to my car with the diode and driving around for a while, testing charging scenarios, etc.!
 
I've used an 18 amp/hr. Powersonic AGM backup battery wired to my bus through a 30 amp fuse and heavy duty toggle switch for about 10 years now. I charge it the first day of every month when I fill the tires up. I load test it once a year and check voltage on it prior to every engine start (checklist item).

No diodes, no relays, not connected to the alternator, minimal parts count.

Along with the toggle switch, isolation from the primary battery and alternator is by turning off the master.

Just food for thought.
 
I've used an 18 amp/hr. Powersonic AGM backup battery wired to my bus through a 30 amp fuse and heavy duty toggle switch for about 10 years now. I charge it the first day of every month when I fill the tires up. I load test it once a year and check voltage on it prior to every engine start (checklist item).

No diodes, no relays, not connected to the alternator, minimal parts count.

Along with the toggle switch, isolation from the primary battery and alternator is by turning off the master.

Just food for thought.

I did a similar set up, 20 AH backup battery but charges while running with a shotski Diode, and monitor both battery voltages on the Dynon
 
I agree that that the battery won't theoretically see any load during normal flight ops, but it will self-discharge a bit in between flights and will be in use while starting the engine. So is the 13.9V downstream of the schottky diode high enough to restore that energy?

I've put the question (minimum float voltage in this application) to the manufacturer, and will report.

Since my plane is still a project, I'm thinking of hooking my aux batt up to my car with the diode and driving around for a while, testing charging scenarios, etc.!

Good for you! One well-crafted measurement is worth 100 opinions.
 
Had a nice exchange with the tech rep. Assuming a float voltage of roughly 13.6, the little AGM battery should settle in at about 90% of rated capacity.
 
Given that EI and EFI are becoming more common, perhaps it's time for our EAB EFIS suppliers to provide two separate voltage monitor inputs with alarms. My faithful GRT Sport SX only has one, thus a requirement for a stand-alone monitor on the second power source (like the Lightspeed drawing). /QUOTE]

Hmmm. My GRT Sport SX currently monitors and alarms for three separate voltage inputs: two to the EFIS and one to the EIS. I have my engine parameter page set up to show all three on the engine parameter page. I typically also show engine parameters on the primary flight display and the map pages in a band along the bottom of the page, where there isn't enough room to display everything, so I only show the primary EFIS voltage input there if I remember right.
Are you mistaken about the SX capabilities or am I not understanding something?

Erich
 
Are you mistaken about the SX capabilities or am I not understanding something?

I could be mistaken...but below is what I learned from GRT a few months back. If there is a way to use the existing panel gear to independently monitor voltage on the second ignition, I'm all ears.

The "EFIS Voltage Bus" inputs are the power supply inputs to the Sport SX. It monitors its own power inputs. It can draw power from any of these inputs, so they're not good for monitoring a voltage to something else. (Also, the SX does not actually have a 3rd power input.)

The Sport units don't have any other voltage measurement pins. If you have any unused Aux pins on the EIS, you can use them to measure voltages. The EIS Aux inputs are max 5 volts, so you would have to use resistors to divide the voltage down into the 0-5V range.

Jeff DeFouw <[email protected]>
Programmer
Grand Rapids Technologies

On 2/26/2017 11:43 PM, Dan Horton wrote:

I’d like to monitor the voltage supply to a pair of electronic ignition systems. When I look at the “Engine Limits” page (screen shot attached) I see setup choices for EFIS Voltage 1, 2, and 3. However, these choices are not mentioned in the setup manual, nor do I know how or where to connect them.

The unit is a Sport SX, 2009-2010 vintage, boot page photo attached.

 
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Tangential to the main discussion, but possibly relevant:

All voltmeters are not created equal. A friend installed dual Light Speed ignitions several years ago, including the dual power supply as described in Light Speed's drawing. Light Speed recommends that the ignitions be wired directly to the batteries, bypassing the master contactor, and that's how this installation was wired. Thus the voltmeter is always connected and reading voltage .

If his plane sat, as they are wont to do at times, the main battery would be dead in about 3 weeks (his power select switch was normally set to the main battery). Disconnecting the voltmeter ground stopped the problem. It could've been an issue with that specific meter or perhaps characteristic of the model he used; I didn't follow up to find out. Just something to be aware of...
 
Tangential to the main discussion, but possibly relevant:

...the voltmeter is always connected and reading voltage....If his plane sat, as they are wont to do at times, the main battery would be dead in about 3 weeks...

Definitely relevant Lars, thanks. When flying with EI, we all know we should not depart the pattern with a less than fully charged battery, but folks do it anyway, human nature being as it is. Making sure nothing drags down a battery while parked is safety by design.

Take a look at the little push-to-test voltmeter diagram. The monitor alarm board and push-to-test voltmeter are not powered when parked. The monitor does bring a small running penalty if alternator out, a 50ma+ draw with the buzzer and LED going, which shortens run time. If I'm alternator out and running on just the 3.5Ah battery, I'm treating it as a "land now" emergency.

BTW, I suspect a creative fellow could tap the board and move the little voltmeter display (used here just for setting limits) to a panel location. Not wanting another cockpit light at night, I will install the push-to-test and add "Poke the button" to the runup pad list.
 
Small panel mount voltmeter

I put one of these in the panel, cost $10 to my door via Amazon prime. I put it in series with a fuse and a small momentary pushbutton. It has 1/4" faston spades on the back. It mounts in a 1.125" hole.

With the efis I can check BAT2 (only purpose is ignition #2) prior to startup, as well as ongoing monitoring for proper charge voltage. I use this panel meter only to check the tiny battery which keeps the efis alive during start. I can also verify it is charging after startup.

YkvDsdaKJ1h-aocDJgRDSBqBP1G3DjOlt28WqsFvoztU6zxivlOgnZqvxAfRKiQqq4SnzFPCFur1Zkuv7AgcfzviJIdTX7lQRLrpfTbP_I6_EmEJxpjFIveOvMoPT-zxFPDRhMNc4Zqovg9QOFu920q0633LGANZhhpiBWDKyjstKvEvxjpztZT_c5oJS6GYVezKsA_I_cGQGauhcPsuDXClqZzi4TZsT9gYKGlHnPAoyGLKOHd8oLDSWMn61OUHDDSQARdCZkpAksBxv1nAL_vthmiR-nWSqzSucvUCDCppag2BgfnP-VoTT7QoQh1H6uYnZTjSmLQ8aDj_UMvetbu13jYtOAS4_dlfJXfrGCc6PyhlDHar7XHw1IpSSC4rQXU60fW7OuR50Ac_zqP8rmxh4f6xukIKNQ1WyLQ4IBLCfCf6tDcxjlJEkh4jg9V2w3LfdyqjMwXX8w4N5uqVinzXOeH7tFgNppWr4qDV_Kl07bfpCF9pyEx8zHhGc5R92kTQMH0HOuvmOOHLfwHsuYe5oFlTNGUbFoWvkwkZNlzL3lRUnPs491EsKi_Aw6J35x1pBPEKG69n0_IUUyZYdSZXSRv_Z-sdetdbx2R3KxF_wG31DdhA=w323-h368-no
 
Well, gosh, we are talking about "Dual Lightspeed install", per your thread title and first post, which BTW, seems to burn Lightspeed for an installation which does not match Lightspeed drawings. As drawn (and as noted by Alan), simply pulling the breaker allows looking at IGN2 battery voltage, at any time. When installed per drawing, there is no reason to be flying with a dead ignition battery.

I think we would like to see why your two batteries and one alternator is better than Lightspeed's two batteries and one alternator. After all, details do matter. Please post your diagram.

There are other ways to provide battery monitoring. Here's a little add-on circuit...one relay, one momentary SPST switch, and a $3 two-wire digital voltmeter display. Pushing the button disconnects BATT2 from charging, and connects to the voltmeter. The VM display, normally dark, lights up and shows BATT2 voltage under ignition load, in flight or any time. Don't even need the master on.



I already have a monitor to alert if BATT2 becomes disconnected from charging, so I think I'll add the above test circuit. Pushing the button will even check the monitor.

http://www.vansairforce.com/community/showpost.php?p=1159312&postcount=166

Please forgive my ignorance. I'm trying to understand a few things.

The wire depicted that runs from the hot side of "BATT CONT" to the relay has no fuse or fusible link. Why?

In this design, how close should the relay be to the "BATT CONT"?

What are the advantages and/or disadvantages of terminating the wire that runs from the hot side of the "BATT CONT" to the switched side of the "BATT CONT"?

These abstract drawings are difficult for me to visualize the actual physical characteristics of the install. I've order the parts and plan to set this up on a bench and fiddle with it to try and understand it better. I may even put it in my truck like someone else here suggested.
 
The wire depicted that runs from the hot side of "BATT CONT" to the relay has no fuse or fusible link. Why?

It does, in reality. The diode has a relatively low current rating. If the wire is shorted to ground anywhere between the diode and the fuse at battery #2, the diode will burn open. If you don't buy that, no problem; install a fuse at the contactor.

In this design, how close should the relay be to the "BATT CONT"?

It can be anywhere.

What are the advantages and/or disadvantages of terminating the wire that runs from the hot side of the "BATT CONT" to the switched side of the "BATT CONT"?

I can't think of an advantage.

These abstract drawings are difficult for me to visualize the actual physical characteristics of the install.

All part of the "education and recreation".
 
It does, in reality. The diode has a relatively low current rating. If the wire is shorted to ground anywhere between the diode and the fuse at battery #2, the diode will burn open. If you don't buy that, no problem; install a fuse at the contactor.

Didn't know that. Thank you.

In my RV-8 the main battery and battery contactor are on the firewall in very close proximity, one to the other. If I placed the diode near the hot side of battery contactor terminal it serves to protect the entire length of wire that runs between the battery contactor and the aux battery. If/when the diode burns open due to a short, the associated smoke should mostly be confined to the engine compartment or exhausted out the cowl.

Thanks for helping me understand.
 
Carl...

Mind sending me a copy of the email you sent to Dan? I'd like to pore over your schematic. Thanks!

sportav8r something gmail. something
 
Carl or Dan,

Can one please put up link of Carl's diagram. I have a collection and am always looking at different ways of doing things. Am sure others would also be interested.

George
 
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