Isolators with a substancial voltage drop require that you move the sense aspect of your internally regulated alternator to the battery-side of the isolator. This is how they deal with the fact that the silicon diodes used in the isolator are inefficient and will drop one to one point five volts as power from the alternator passes through the isolator on its way to the battery.
I just did a dual battery conversion on my '94. I used the isolator you are talking about. Works very well, with only about a 1/4 volt drop. Just be sure to use high quality wire and solder all of your connectors.
Carefull...... 1/4 volt drop at what current level? As the current goes up, so does the voltage drop. As the current goes up and voltage drop goes up, so does the heat....it gets to be a downward spirol so just be aware of those performance dynamics.
I just did a dual battery conversion on my '94. I used the isolator you are talking about. Works very well, with only about a 1/4 volt drop. Just be sure to use high quality wire and solder all of your connectors.
If you have plans to upgrade your alternator for a higher amp capable in the future, or even to have peace of mind with your OEM alt, I would install a bigger isolator like the Surepower 16023A . Since it can handle 160 amps, came with a big aluminum heatsink you will have a very low voltage drop even at the maximum rated amp output.
I would also increase the gauge of the actual wire which goes from the alternator positive output post to the isolator, even if you keep your stock alternator.
I am by no means an electrical expert, so feel free to correct me as to any inaccuracies. My understanding of these selenoid based style of isolator/combiners is that at rest, (batteries isolated) there is no voltage drop or usage, as the contacts are normally open. Also, if you are using accessories from either the primary battery or secondary battery, there is no additional voltage loss because the batteries are still isolated and the isolator/combiner is not energized. Only when the batteries are combined will you get the additional voltage drop associated with the voltage necessary to close the contacts. If combined automatically with the rig running, the alternator would more than make up for the minor voltage loss associated with keeping the contacts closed.
I installed the Surepower and wiring harness offered by IPOR (one of our board sponsors). He offers the whole kit including isolator, battery box and wiring harness. Easy install.
I am by no means an electrical expert, so feel free to correct me as to any inaccuracies. My understanding of these selenoid based style of isolator/combiners is that at rest, (batteries isolated) there is no voltage drop or usage, as the contacts are normally open. Also, if you are using accessories from either the primary battery or secondary battery, there is no additional voltage loss because the batteries are still isolated and the isolator/combiner is not energized. Only when the batteries are combined will you get the additional voltage drop associated with the voltage necessary to close the contacts. If combined automatically with the rig running, the alternator would more than make up for the minor voltage loss associated with keeping the contacts closed.
If you go for a solenoid aproach there should not be any drop voltage when the solenoid is energized unless the solenoid is under rated for your purpose or the contacts are pitted.
The voltage drops happen when using electronic isolators which resort to a diode which works as a check valve allowing current to flow only on one direction and this "check valve" has a toll of 0.7 volts , means voltage measured at the output of the isolator will be 0.7 less than at the isolator input.
Since the Land Cruiser alt has a internal regulator, it senses the ouput from the output post (same as the battery voltage) and regulates the alternator output voltage, but when you install a electronic isolator designed for this type of alternators, the isolator came with a aditional post, besides the Alternator input and battery 1 and 2 outputs, to which you will hook the alternator voltage sense wire which will trick the alternator to ouput 0.7 volt more to it´s rated voltage ouput to compensate the isolator drop.
By the wy some manufacturers now use Shotky type diodes which has less droping
If you have plans to upgrade your alternator for a higher amp capable in the future, or even to have peace of mind with your OEM alt, I would install a bigger isolator like the Surepower 16023A . Since it can handle 160 amps, came with a big aluminum heatsink you will have a very low voltage drop even at the maximum rated amp output.
I am by no means an electrical expert, so feel free to correct me as to any inaccuracies. My understanding of these selenoid based style of isolator/combiners is that at rest, (batteries isolated) there is no voltage drop or usage, as the contacts are normally open. Also, if you are using accessories from either the primary battery or secondary battery, there is no additional voltage loss because the batteries are still isolated and the isolator/combiner is not energized. Only when the batteries are combined will you get the additional voltage drop associated with the voltage necessary to close the contacts. If combined automatically with the rig running, the alternator would more than make up for the minor voltage loss associated with keeping the contacts closed.
The mechanical contacts efficiently transfer current when they're new, but every time the contacts open and close, arcing occurs. Over time, the contact surfaces gets pitted as deposits of carbon get deposited and what started as a low voltage-drop contact surface eventually become a high-resistance contact surface. High resistance yields heat and excessive heat is what will be the demise of relay. This is why, in many applications, going to a solid-state method of isolation is interesting. In solid-state isolation, the use of silicon and Schottky diodes have been used, but there are tradeoffs. The voltage drop through silicon diodes is horrendous, but with large enough diodes and enough aluminum strapped to it, it can serve the purpose. Schottky diodes have less voltage drop, but still drop half a volt and suffer from substantial leakage. They still require a large heat sink because they too get hot and throw away quite a bit of power. The third type of solid-state isolator uses MOSFETs. It can handle large amounts of power with no heat-sink and has a voltage drop in the 20,000ths to 40,000ths of a volt drop, but there's a tradeoff there as well......they're not cheap. Those are the various options available so now you gotta hit the net, see what's out there, and figure out what's the best fit for your application and budget.
The mechanical contacts efficiently transfer current when they're new, but every time the contacts open and close, arcing occurs. Over time, the contact surfaces gets pitted as deposits of carbon get deposited and what started as a low voltage-drop contact surface eventually become a high-resistance contact surface.
Your understanding is good, but the suggestion that if you use a massive heatsink, it will decrease the voltage drop is incorrect. The heatsink aids in the dissipation of heat that gets generated due to the voltage drop across the rectifier. If your voltage drop at 200 amps is 1 volt, you can strap 500 lbs of aluminum and your voltage drop at 200 amps will still be 1 volt. The aluminum is simply an attempt to keep the device cooler so it survives longer.
Pitting of the contacts within the solenoid will occur when breaking large amounts of current. If you combine (connect) a discharged battery and a fully charged battery, they will want to equalize in charge. So current will flow from the charged battery to the discharged battery as fast as the charged battery can supply - meaning A LOT of current. When you break this connection, or open the solenoid, before the batteries are equalized you're interrupting a lot of current. This is when the arcing will occur. Over time pitting and oxidation will arrise on the surface of the contacts. The pitting and oxidation equal resistance. So over time, the solenoid contacts will become less and less efficient.
True, in the electric utility - the people you pay for your electricity, alkanite contacts are used along with certain methods to extinguish the arc in a very efficient manner. Meaning they can extinguish large amounts of current and last a long time. Most of these contacts are submerged in an insulating oil or surrounded by an inert gas to aid in the extinguishing of the arc. The current I'm reffering to can be as much as 2000amps at 220kilovolts AC.
Smaller solenoids are used in the trade as well which break current below 100amps at 135v DC. These contacts need cleaning to be efficient, and they don't operate as often as your dual battery solenoid would be.
Your understanding is good, but the suggestion that if you use a massive heatsink, it will decrease the voltage drop is incorrect. The heatsink aids in the dissipation of heat that gets generated due to the voltage drop across the rectifier. If your voltage drop at 200 amps is 1 volt, you can strap 500 lbs of aluminum and your voltage drop at 200 amps will still be 1 volt. The aluminum is simply an attempt to keep the device cooler so it survives longer.
You are absolutely right, voltage drop will be the same, I was in a rush when I was writing the post but the main purpose of my sugestion was based on what I noticed on many dual battery instalations were the Isolator was in the 80 to 95 amp range (Cruiser with stock 80 amp alternator) and most of them ended damaged because of poor thermal exchange.
A well designed and bigger capacity isolator will reduce the chance of it suffering damage because overheating.
For example in my Cruiser I use a Powermaster large case #42280 170 amp bench tested (This output would be somewhat less in the real life because the internal alternator voltage regulator will limit it´s output, knowing the alt case temperature when in the motor bay will be way higher versus the one measured when it was rated in the bench) hooked to two Surepower dual battery isolators of 240 amp capacity each one (alternator ouput goes in parallel to each A input post so in theory I can charge up to 4 batteries.
