DC to DC charger or FET isolator for thruster

[bud37]

I would like to charge the thruster battery from the windlass wiring while underway but don't want any chance of back feed to the windlass when it is operated.That is the general idea of it, I am trying to avoid running giant cables all over.

I have seen something called a dc to dc charger....anyone know how they work ? Will an ACR like something from Blue seas work for this ?

I can charge it from the house charger one leg with a cable, but I think underway is the way to go....opinions??

[Midnightsun]

Do you have a thruster now and if so how is it hooked up and charged? An ACR is probably your best bet as it will combine the 2 when charging and disconnect once charged. You can also set it to prioritize one battery if you so desire.

[bud37]

Source of the post Do you have a thruster now and if so how is it hooked up and charged? An ACR is probably your best bet as it will combine the 2 when charging and disconnect once charged. You can also set it to prioritize one battery if you so desire.

Yes...we had it charging from the windlass, but I disconnected it...just didn't like the way it can backfeed when conditions are right.

Hans , I am not ashamed to admit it, but I have never in all these years had a battery isolator, or an ACR and don't really understand exactly how they work. How would the ACR react if the windlass was used...would there be a power loss at the thruster battery bank.Only just found out there was such a thing as a DC to DC 12v charger, but they really don't explain much in the ads.

If I could figure out how to draw on here it might be easier.

[km1125]

One of the things you want to figure out is how fast you want/need to recharge the thruster battery if you've run it down. Do you know what size it is (in AH)?

There are a couple options on the DC-to-DC converters. One is a simple converter that just takes input voltage and converts it to an output voltage up to a certain number of amps. You set the output voltage but the input could vary, lets say down to 10 or 11 volts (could be due to voltage drop) but the output could be a consistent 13.6VDC. This is nice when you have a long cable run but still need the proper voltage at the end. The DC-DC converter will pull more amps from the source so it can deliver the correct voltage. The downside is that you need some cut-off in place or you can drain your source dead if it's not being recharged.

They do make DC-DC converters specifically to charge batteries like in your situation, but they can get expensive. They also have some of the protections in for the source (cuts out below a certain voltage), they can deliver the 3 or 4 stage charging that batteries like, and can also be disabled remotely (like from a signal from your windlass that says it's "in use")

ACRs are just really "smart switches". They are voltage controlled, so if either side of the ACR has a voltage that indicates a charger is working, then it connects the one side to the other. When it senses that the voltage has dropped, as if a charger isn't available, then it opens the connection between the two sides. You can also get them that have a "forced disconnect", which opens the connection regardless of voltage. Some use this for a "start isolation" which opens the connection when you're starting the engines (so that the starter "surge" or "dip" doesn't affect the house loads), but you could use this to open the connection if your windlass was in use.

[bud37]

KM , thanks for the explanation...as for the ah, not sure they are 2x group 31 agm starts.

The ACR forced disconnect , is that automatic or do you have to switch it yourself ? The charging will be done as the boat runs along, from the alternators, at least that is my idea....you really don't pull the thruster batteries down that much in general.

Was going to use a simple battery isolator that has a diode, that way nothing gets back, but soon realized the diode has a downfall of a voltage drop across.

[km1125]

A diode would be not a very ideal solution as it would not really allow the battery to ever become fully charged.

The ACR 'forced disconnect' can be done manually with a switch or you can wire it into some of the existing wiring so it activate automatically. The original purpose for this feature was to wire it to the "start" lug on a key switch so when you were actually cranking the motor it would disconnect the ACR. Once the engine started, the ACR would reconnect.

Need to understand your concern for "backfeeding to the windlass" more. What is the actual concern? The windlass is "protected" by the two solenoids that activate the motor in either direction, so when it's not running there really is no connection from the battery to the windlass. You could say it's "self-isolating" by having the solenoids there.

There is probably more value in having the windlass and thruster operating on that battery bank than there is in trying to isolate the two, and then just use the old "windlass" leads as the charger leads for that battery bank , rather than the supply for the windlass.

[bud37]

Because there is a + and - from the windlass terminals to the thruster batteries, they are joined which actually works fine as the charge gets to the thruster batteries from both the shore power and the engine charge.

So that I am happy with.....when you open the breaker to turn off the windlass that is isolated but now the windlass can pick up power from the thruster batteries..I tried it with the deck foot switches, that is what started all this drama......so even that is not too bad so long as the joining cables are large enough ( I have only 8awg there ),

I hear ya on running the windlass from the thruster, I have actually considered that but am trying to keep the factory control system for the windlass and the charging seemed easy at the time.

Clear as mud heh....

[bud37]

I have come across something called an Argo FET isolator from Victron, it appears to not have the V drop and heat issue of the diode ones......this may work, after a long and very informative discussion with Blue Sea tech, those ACR's are not the best solution for this particular application, because of the back flow and thruster high amp initial draw.....nice guy and good help....

Still mulling over the options..work in progress, opinions always welcome.....

[km1125]

FET isolators are a big improvement over a regular diode isolator, but are more like a remote one-way switch. They do not "self activate" like a diode isolator. A diode isolator will automatically allow current to flow only one direction as long as the input voltage is about 1.2 v higher than the output voltage (that's the voltage drop). If the voltage difference is less than that, then no current flows either direction.

A FET isolator requires an "energize" port to have voltage to turn on the FETs. The FETs are just electronic switches. You would normally connect that "energize" port to the ignition switch of the motor, so when the motor is turned on and running the FET isolator would be activated and it would allow the alternator to charge the batteries. This would work in your application if you ran a wire from the FET isolator back to the ignition.

However, since the FET isolator is an electronic device and you would have two fairly large motors on both sides of it, I'd want to send a diagram of the connection to the Victron folks to see if they have any concerns about "back EMF' from either of the motors damaging the FET isolator. Every time those motors kick on and off they generate voltage spikes in the circuit. The group 31 batteries may buffer enough for the thruster, but the winch may not as much. The manufacturer may have built enough protection into the device to tolerate it, but I'd want them to acknowledge that before I put one in so if it failed I could get a warranty replacement.

[bud37]

KM and Hans thanks for sticking with me on this.It really helps to bounce ideas back and forth to problem solve. The back signal from the thruster motor is what the tech guy at Blue Sea mentioned as could damage the ACR type devices.

My understanding so far as to the energize circuit is, it is there to provide 12v to the engine alternator so it can start working......some alts don't self excite.

It really doesn't apply in this case...I called Victron and they want an e mail describing the set up.....my guess is they are going to refer it to the home tech guys in Europe. I will make a schematic and we will see what product they have that may work here.

All of the products so far won't work because the engines are running so the circuits will be made and even after shut down the threshold for cut-off is 12.75 or so, now that takes a while to drop to that point before the circuit is open. The only thing close is the isolator....need to find out how hot those things get.....he couldn't tell me..