Battery doctor 140 amp isolator

[Burbanlife]

I currently have 200 watts of renogy panels , 12 volt system, a 100 ah agm/sla battery.   Now  here is the question ....I have just picked up a Battery doctor 140 amp battery isolator to use with this set up on my 2002 suburban. I will have a pretty constant load on the aux battery with fridge and a another 120 volt item that draws approx. 5 amps that will be plugged into the power inverter.  I want to see if that would be ok to use, as I have heard that these isolators can burn up an alternator pretty quick.   thanks

here is the isolator link https://www.amazon.com/gp/product/B0058SGDFK/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

[John61CT]

Proper term is ACR, also VSR or combiner. Isolators are diode based and usually cause a significant voltage drop.

They don't do anything with charging, just decide to pass the current between House circuit and Starter batt based an high voltage, showing charging is going on.

This is by far the best kind to get, very robust will last forever

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

 

[John61CT]

Whether charging a depleted House bank will cause problems with your alt or just cause it to stop charging when heat protection kicks in, has to do with lots of variables.

Likelt not an issue if the bank is lead and not huge, unless you have recent Euro super Eco features like regenerative braking.

In which case look at DC-DC chargers like CTEK and Sterling's batt2batt units.

 

[MrAlvinDude]

I want to see if that would be ok to use, as I have heard that these isolators can burn up an alternator pretty quick.  

Where did you hear about them causing alternator wear / burn out ? 

I would think that such an "intelligent" battery isolator would actually lower the wear on the alternator, compared to having two batteries directly connected to the alternator at all times. 

One of the two main jobs for such an isolator is, to make sure that only one battery is available for charge,  in the case that the starter battery needs an extra heavy charge. And thus an "intelligent" battery isolator actually makes sure that the load on the alternator is spread out.

 

[frater secessus]

The battery doctor unit, as has been pointed out above, waits until the starter battery is at a decent level before connecting to the house battery. This should ease the load on the alternator. I still wouldn't idle the vehicle to charge -- if I remember correctly SternWake installed an external fan on his alternator so he could charge at idle without heat stressing it.

[edited to add - I have the 80A unit and it works fine]

 

[Burbanlife]

Where did you hear about them causing alternator wear / burn out ? 

I would think that such an "intelligent" battery isolator would actually lower the wear on the alternator, compared to having two batteries directly connected to the alternator at all times. 

One of the two main jobs for such an isolator is, to make sure that only one battery is available for charge,  in the case that the starter battery needs an extra heavy charge. And thus an "intelligent" battery isolator actually makes sure that the load on the alternator is spread out.

I was just browsing the web, it was not this particular unit  the battery doctor but battery isolator in general . I did  not save it , I was doing searches about them and found it, so I can not give a location as to where I found that write up.

 

[Burbanlife]

My main concern is since there will be a load constant load on the house /aux battery while driving would be the strain on the alternator and the battery doctor since it would possibly switching back and forth a lot or just keeping the alternator putting out current most of the time. Hope that makes sense. thanks

 

[frater secessus]

It doesn't take long for an alt to get the house battery as charged as the alt can get it (about halfway through bulk). I don't think it's anything to worry about.

The Battery doctor will engage when the starter battery is above a given point then disengage after about 60 seconds after the starter-side voltage falls back down below that (ie, engine not running). I haven't seen the setpoint published but I suspect it's between 13.4v and 13.6v. It engages quite soon after my engine starting.

 

[John61CT]

I would think that such an "intelligent" battery isolator would actually lower the wear on the alternator, compared to having two batteries directly connected to the alternator at all times. 

One of the two main jobs for such an isolator is, to make sure that only one battery is available for charge,  in the case that the starter battery needs an extra heavy charge. And thus an "intelligent" battery isolator actually makes sure that the load on the alternator is spread out.

There are units that claim to do that, but none actually do. On the best (value) units the only intelligence is voltage high close, low open.

And it's just a marketing checkbox anyway, since that is in reality not a real problem.

Cranking the engine is such an infinitesimally small load compared to House, if Starter is actually dedicated to just that task in normal usage it hardly ever needs (nor will accept) more than a 5-10A trickle.

That's why a good design puts as many charge sources direct to House, then an Echo Charger is plenty for Starter.

Most don't want to spend the money doing this for Alt, which in most cases is a minor charge source anyway.

A bigger ACR also allows for self-jumping when needed - should be never, if the system mainteneance is being done right no surprises.

Charles Sterling has put out some unnecessarily fear-mongering marketing on the topic, but while his (Promariner's) multi-bank combiners are perfectly fine, they aren't good value for money. Although he makes a current-limiting version that would be interesting for some use cases.

PS the term "isolator" refers to one-way usually diode based units, out of favor these days due to voltage drop issues. Newer exceptions are very expensive, but also not suitable for the OP use.

 

[John61CT]

I still wouldn't idle the vehicle to charge

Not a problem for just a short time once in a while.

But as a regular thing way too much wear and tear for most vehicles, cheaper to get a little genny.

 

[Reducto]

As mentioned, the only thing that MIGHT kill the alternator is if you spend a lot of time idling to charge a near dead house battery. Under normal use you're just fine.

I had this same battery doctor for a while and the only problem I had was when I switched to a van with a 145 amp rated alternator. When my house batteries were very low they would pull enough current to trigger the protection circuits on the isolator. I would get no charge under those conditions. Unless you have a big alternator and big battery that probably won't happen to you but it would be a good idea to have a voltage monitor so you can see when it's turning on and off.

 

[John61CT]

Actually you **have** to make sure the max Amps rating gives 10-20% headroom compared to what will be passing through the ACR.

Otherwise it will burn out, usually contacts welded in closed position.

This is one reason the Blue Sea ML model never fails, thousands of installs decades in marine conditions, just too robust.

___
It is very common for a very large high CAR bank to demand such high output that stock alts blow their diodes.

But that's not a problem to do with the ACR, unless you want to solve it by finding a current limiting version.

IMO far better to get a more robust Alt, and / or a good programmable external VR.

Next best is going to a DC-DC charger unit, lots cheaper and easily moved with the bank to the next vehicle, or a boat, off-grid cabin whatever, compensates for the weaknesses of many standard charge sources, and adjustable for any future bank chemistry.

 

[Reducto]

This is a transistor based isolator, not a solenoid. If you try to go over current it simply shuts off so damaging it should not be an issue. Your batteries just won't be charged under those conditions. It resets itself after voltage goes down below the charging threshold.

 

[frater secessus]

Not a problem for just a short time once in a while.

Sternwake's testing showed overtemp conditions when idling and normal temps when driving, leading him to put a fan on his alternator.

 

[ZacLee]

Keep in mind that a standard automotive alternator will not produce anything near its rated output while running at idle speed. Also, electronics in a typical modern car might draw 20A or so while running assuming headlights and the hvac blower are off. Idle output is typically 40A for a 125A rated alternator and full rated output is only achieved when the engine rpm is above 2000-2500.

Alternator output ratings are also generally optimistic. I've seen 145A rated alternators with 8 (or even 10) gauge wiring. alternator. In that case, the wire would overheat if a high current loan were sustained.

 

[Burbanlife]

My other question about using the Battery doctor or any other isolator is this...my agm battery says not to have a charging current of more than 20 AMPS.

How can I find an easy way to find out the exact amount of current going to the aux. battery or would that be something I really dont need to worry about?

 

[John61CT]

Something you really needn't worry about.

As long as volts are controlled, lead batts are self-limiting.

My theory is lawyers

 

[Burbanlife]

Something you really needn't worry about.

As long as volts are controlled, lead batts are self-limiting.

My theory is lawyers

Thanks John61ct.  It did fine today , so all is good , now maybe you can ease my mind on this, I have a 100 ah agm currently but Wednesday I will have another one in parallel so a total of 200 AH,    would this 150 amp isolator be too small?  that just came to my thought process. thanks

 

[John61CT]

Nothing to do with bank capacity.

What is the biggest current you anticipate ever crossing from one circuit to the other?

 

[KathyC]

This is by far the best kind to get, very robust will last forever

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

I have a four wheel camper that came with this ACR...it's fantastic.  In fact, Four Wheel now installs these on all their new builds.