Battery Isolators

[bpdchief]

WirthCo 20090 Battery Doctor 75 Amp/100 Amp Battery Isolator vs [size=large]NVX BIR200 200 Amp Relay Isolator (BIR200) /Stinger Equivalent....  electronic switching control technology vs mechanical [/size]

[size=large]Is the alternator in more danger of burning up with the mechanical switch due to charging two batteries. My plan for the time being is to use one 12v deep cycle battery for a house battery - 100 watt solar panel and support charge while driving.[/size]

 

[John61CT]

I'm not familiar with either, but the "alt burning up" is not a thing no matter what.

​ https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A

is the good stuff.

If you know your max ampacity, there are dozens of adequate others cheaper, but nothing beats that one for longevity and reliability.

 

[frater secessus]

WirthCo 20090 Battery Doctor 75 Amp/100 Amp Battery Isolator vs [size=large]NVX BIR200 200 Amp Relay Isolator (BIR200) /Stinger Equivalent....  electronic switching control technology vs mechanical [/size]

[size=large]Is the alternator in more danger of burning up with the mechanical switch due to charging two batteries.[/size]

Dunno about the NVX, but the Wirthco waits until the starter battery voltage has recovered before it starts charging the house battery.  So it is effectively only seriously charging one at a time. I have one and it works well on my FLA bank.  AGM or lithium might want more than 100A.  

IIRC Sternwake was of the opinion that it was idling to charge is what causes alt failures (insufficient cooling when stationary).

 

[Weight]

I'm not familiar with either, but the "alt burning up" is not a thing no matter what.

Information about automotive alternators and deep cycle batteries. Scroll down a bit to see the result if using a large bank. http://www.pbase.com/mainecruising/automotive_alternators_vs_deep_cycle_batteries

 

[John61CT]

Running your Alt hot while the vehicle is sitting still at low rpm without a good external regulator like that MC-614 can easily fry alt electronics.

With proper infrastructure the problem will be lack of output, not damage to the alt.

But none of these issues has anything to do with using an ACR / VSR.

That is the misconception I was correcting. Yes high sustained amps throughput may damage your combiner, or damage your alt's diodes, but the alt is never damaged by your choice of combiner.

Running a big propulsion engine just to charge your House bank is silly IMO, wear and tear is very expensive, just carry a small genny.

The need for a proper Alt and infrastructure to do significant House bank charging even when underway is a lot more than most people are willing to invest even on yachts.

 

[John61CT]

And the combiner / ACR / VSRs you're discussing here never come up in the marine forums.

Automotive gear is usually far lower quality than that sold for marine use.

And Maine Sail specifically recommends the same Blue Sea unit I posted above.

As I said there are dozens of cheaper units available I can recommend that are also better, but you do need to spec the max ampacity needed to pass through.

Self jump starting requires supporting momentary 200+A loads for example. Many HO Alt setups get up to 300+A charge rates for around 10-20 minutes, but LFP may sustain that for over an hour.

Anything close to those needs I'd stick to that ML-ACR

 

[user 37446]

All good info above, especially marine quality parts being superior. When you are out on the water and your very life may depend on getting back, well, your parts quality is important!

Very unlikely any decent quality isolator/solenoid will fry anything or get fried. If you look at them on Amazon, you will see some lower priced, lesser amp units (solenoids) and some obviously better ones, though there's not a great price difference.  There is also another kind, called the Wirthco 20092 Battery Doctor, it has two different amp levels, so purchase the higher model if you can.

There are ways to limit how much current flows into your depleted house battery, that can be done through wire resistance. IE if you want fast bulk recharging you use thicker, pure copper wires (stranded). Sizes like 1/0.  If you want a lesser amount coming in that's still safe (depending on the length of cable), try something like 6 gauge, again, stranded copper preferred over CCA (copper clad aluminum).

Remember that your automotive wiring is not all that thick anyway, from a car repair forum: "according to a google search a general rule is 70-75 amps for 8 gauge wire, 100 amps for 6 gauge. but those are likely pretty conservative ratings"

Most FLA batteries don't readily accept huge inputs of power (really high quality AGM deep cells do but most of us don't have those), so there's a built-in limitation there as well.  All in all you shouldn't worry about your proposed system, given it is installed and fuzed correctly.

 

[John61CT]

> There are ways to limit how much current flows into your depleted house battery, that can be done through wire resistance

But why on earth would you want to do that?

Potentially dangerous too.

Ideally all significant charge sources should output directly to your House bank.

If you bother with a dedicated Starter batt, that barely gets depleted at all in normal use, a little 5-10A source will maintain that no problem.

The whole "big surge when connecting depleted House to full Starter" is a total red herring, not an issue IRL at all.

 

[highdesertranger]

reminder, the manual disconnect switches CAN damage your alternator. if you switching the alternator feed you must have the "make before break" type of manual switch or you must NEVER switch while the engine is running. highdesertranger

 

[John61CT]

Principal idea being alt output must have someplace to go.

Blue Sea's have an AFD - alt field disconnect - feature available which effectively turns off alt before isolating the bank. You would likely want help from a DC sparkie to make sure it's wired properly.

Or have a cheap lead batt hardwired to the alt output.

Most just hardwire the alt output direct to the target bank, along with other "always on" alarm & safety loads, clock/radio memory etc.

But none of this has to do with using combiners / ACRs / VSRs.

 

[user 37446]

Principal idea being alt output must have someplace to go.

Blue Sea's have an AFD - alt field disconnect - feature available which effectively turns off alt before isolating the bank. You would likely want help from a DC sparkie to make sure it's wired properly.

Or have a cheap lead batt hardwired to the alt output.

Most just hardwire the alt output direct to the target bank, along with other "always on" alarm & safety loads, clock/radio memory etc.

But none of this has to do with using combiners / ACRs / VSRs.

last sententence true, I just remember SternWake speaking about slightly reduced sized wiring (not to the point of dangerous, ie: 6 guage vs 1/0) limiting what the battery will accept, same with non-AGM not accepting large rushes of amperage. Of course, very few standard alternators out there will dump in more than 80-100 amps for more than a few minutes (when cold) anyway.

Tis' true that you can't just shut the house battery off without thinking.  I like the combiner type "Battery Dr." products as they cause the 2-3 batteries to be seen as one big battery to the alternator, so there's usually always something taking current.

 

[HumbleBeginnings]

For what it's worth, I've been using this isolator for a month or two and I'm loving it.  

I chose this particular one because I saw it recommended by a few different sources. I can't speak to longevity yet, though.

 

[John61CT]

> I like the combiner type "Battery Dr." products as they cause the 2-3 batteries to be seen as one big battery to the alternator, so there's usually always something taking current.

True for any of them.

 

[bpdchief]

Thanks to all for your input... so much knowledge on this forum, it's amazing!!

 

[ZacLee]

Disconnecting the battery while being charged by the alternator causes a large voltage spike from "load dump":

https://en.wikipedia.org/wiki/Load_dump

In general, I prefer battery isolators that use latching relays because a latching relay only consumes energy when switching states. Unlike a conventional relay, it require no energy to stay in a particular state. It only requires energy to change the state. Solid state (typically MOSFET) switches have some advantages, but are less robust than mechanical relays and are also less energy efficient, as evidenced by the heat they dissipate.

 

[John61CT]

Isolator usually means one-way diodes.

Combiner, ACR/VSR functionally the same, but each model has slight differences.

None will isolate a running charge source from either bank, and even when isolating the banks from each other, each charge source will still be connected to the bank on its side.

Assuming gear's all installed properly.

And yes that Blue Sea ML ACR is the best, even if overkill for most needs.

Again, I have detailed notes on dozens of other types not as expensive, but you need to specify max continuous amps desired.

And note all of these above are "voltage following, just like charge sources with multiple bank outputs, all banks need to require similar charge profiles.

If different enough chemistries and both banks are valuable, then you need to upgrade to DC-DC chargers, more sophisticated but a lot more expensive if high amps required.

 

[ZacLee]

On the other hand, this doesn't need to be so complicated or expensive. One wants the deep cycle batteries to be connected (in parallel) with the engine starting battery when the engine is running, but otherwise disconnected. This function could be achieved with a simple relay controlled by the ignition switch.

 

[John61CT]

OP mentioned solar.

Installing a proper dual-sensing VSR / ACR is no more complex, and you don't need to change anything as you change / add charge sources later, to either side.

 

[HumbleBeginnings]

On the other hand, this doesn't need to be so complicated or expensive.  One wants the deep cycle batteries to be connected (in parallel) with the engine starting battery when the engine is running, but otherwise disconnected.  This function could be achieved with a simple relay controlled by the ignition switch.

The reason I personally did not go with this method is because the drained battery is connected at the instant you're trying to pull your cranking amps to start the vehicle. I don't have the background to know how big of a concern that is, but I had been warned away from that method so I went with the battery isolator.

 

[Reducto]

I used a Battery Doctor 125 amp isolator in my old van. I transferred it to my newer van with a 150 amp alternator and it would not work if the house battery got too low. As soon as I revved up the engine it would go into protection mode and shut down. Seeing as those were the times I needed a charge the most, it was pretty useless to me.

I switched to a Blue Sea isolator and love it. The only thing I don't like is that it keeps switching on to charge my van battery when the solar panel is active. I'll eventually get around to hooking up the switch so I can disable this when parked.