Verifying the operation of dual alternators

[ADWSystems]

My brother posed a question to me tonight as he was taking a break from replacing both batteries and alternators in his truck. According to the shop, one alternator died a while back and the other kept ticking. Now either one of the batteries failed or started to failed and overloaded the remaining alternator and then the engine overloaded the batteries. So both alternators are shot as well as the batteries.

Fool me once, shame on me. Ain't going to fool me twice.

The question posed is how can he tell if one of the alternators fails? Both alternators are literally directly connected to the battery (alt 1+ to battery + and alt2 + to battery +, and both batteries in parallel). And yes this is a big truck, F350 7.xL diesel.

The shop says to install an ammeter, but they are forgetting they are 150A alternators, which means two shunts and two meters. Twice the wiring and stuff to futz with.

My thought was to place a large diode between each alternator and the battery that would then allow a voltmeter or light to be installed (between alt. and diode) to indicate it was functioning. What do you all think?

 

[ronsimpson]

Some motor homes use a diode. Battery 1 is for use with the engine. Battery 2 charges through the diode. Battery 2 is used for lights & TV in the back. This way if battery 2 is fully discharged the engine still has power.

 

[Boncuk]

Hi,

I recommend to have a look into the Allegromicro ACS758ECB-200U-PFF-T.

It's a unipolar current sensor with a resistance of 100µOhm of the inernal conductor.

The max current is 200A and the resolution is 20mV/A.

Use two OpAmps to amplify the input voltage to e.g. 200mV (corresponds to 10A current flow) and comparators to lit an LED when current is flowing towards the battery and into on board loads.

Boncuk

 

[4pyros]

You need Battery Isolator's like this;
http://www.colehersee.com/home/grid/cat/211/

 

[ADWSystems]

Hi,

I recommend to have a look into the Allegromicro ACS758ECB-200U-PFF-T.

It's a unipolar current sensor with a resistance of 100µOhm of the inernal conductor.

The max current is 200A and the resolution is 20mV/A.

Use two OpAmps to amplify the input voltage to e.g. 200mV (corresponds to 10A current flow) and comparators to lit an LED when current is flowing towards the battery and into on board loads.

Boncuk

I like it. Too bad it's not a contactless solution. The currect has to run through the chip which will mean making something to attach it to including a way to attach the cable to/from the alternators.

Any thoughts on a contactless option?

(the stud diodes I was looking were bolt on/in and all I would need to do was keep them isolated from the truck chassis/ground)

 

[tcmtech]

I don't think isolating one battery is a good idea on a Ford diesel. They need both batteries together to start being they can easily draw well over 1000+ cranking amps when cold which is at the limits that any single battery that can fit in a common pickup engine compartment can support.

As far as the two alternators giving up at the same time thats rather normal on dual alternator equipped Fords as well. I think its because the share common exciter and related circuit connections so when one dies it back feeds the second units regulator until it fries too.

The way I look at it is if you cant afford to fix your vehicle you cant afford to own it either. The fact is bigger stuff costs more to fix.

 

[jpanhalt]

What is the voltage drop across the big diodes you anticipate using? Perhaps you could use that drop (0.7V?) with a joule thief (https://en.wikipedia.org/wiki/Joule_thief) wired in parallel to light an LED on the dash.

There are many circuits for joule thief's you can find on Google. Some work with voltages well below 0.7V.

John

 

[ronsimpson]

What is the voltage drop across the big diodes you anticipate using? Perhaps you could use that drop (0.7V?).........../QUOTE]

With a 125 amp alternator and a silicon diode eating up 0.7 volts; thats 70 to 90 watts in the diode. ouch! Years ago we used germanium diodes with much less drop. In my last switching power supply I used synchronous rectification with 0.05 volt loss.

 

[jpanhalt]

I have seen joule thief circuits to 0.35V. I think we need more information form ADWSystems, since he apparently has a specific type of diode in mind (post#5).

John

 

[ronsimpson]

https://www.powerstream.com/battery-isolator.htm
???????????

 

[alec_t]

Perhaps use a Hall effect sensor appropriately orientated next to the main current bus to/from the alternator?

 

[ADWSystems]

I have seen joule thief circuits to 0.35V. I think we need more information form ADWSystems, since he apparently has a specific type of diode in mind (post#5).

John

I came across this diode: https://www.electronicsurplus.com/Item/30925/MOTOROLA - 600V Stud silicon diodes_ - MR1229SL/

200A 0.4V drop with a decent termpature rating.

Keep in mind that I'm looking to isolate the two alternators from each other not the two batteries. Presently all four positive terminals are connected (A1-A2-B1-B2) together. I would lke to isolate the alternator outputs from each other; not to prevent backfeeding directly, but to be able to detect when one has died (ditection is not possible with a voltmeter because of the backfeeding). As mentioned originally, the FMEA of the situation is that one alternator dies but you don't know it until the battery is at a weak point (perhaps after starting on a cold morning) and hit it with a large load (turning on all the lights and high beams) at which time you overload and kill the second alternator, then with no charging system you overload and harm and kill the batteries. The root cause is one alternator died and you had no idea it had happened.

 

[ADWSystems]

Perhaps use a Hall effect sensor appropriately orientated next to the main current bus to/from the alternator?

I'm game. I scoped out some solutions, but they all look like I need to create my own sensor assembly which I'd prefer not to do. Any leads on a pre-made assembly for DC current?

 

[Reloadron]

Canned solutions like these aren't quite cheap at about $100 USD per copy. Then there is the matter of powering it with something like this or similar DC / DC converter with a wide input range and those run about $32 USD. So what you have is a little under $250 USD for the ideal canned solution. Then too for those of us who love and drive trucks cheap at the price for a canned solution. I can't buy two batteries for that price let alone replace a single alternator.

Ron

 

[ADWSystems]

I saw a similar thread that mentioned the CR Magnetics parts. I hadn't ruled them out on price, only on operating range (0-122degF). I didn't think that would cut it under the hood of a truck. Automotive temperature range is to +302DegF (150degC). A far cry from the ability of these. From the DIN mounting spec, it is apparent their typical usage is in a control panel in a building.

What would it take to gang a Hall Effect IC and core? Keep in mind the design constraints would need to include only a single pass through the core (ie., no extra loops or turn due to the wire gauge and only need to turn on a light (green is go).

P.S. IIRC the total repair bill on this was just over the $800 mark for the two batteries, two alternators, and a new belt (might as well since it's off anyway).

 

[4pyros]

I came across this diode: https://www.electronicsurplus.com/Ite...0- MR1229SL/

200A 0.4V drop with a decent termpature rating.

Good price but you are still going to need a big, BIG heat sink.
By all rights you should bust the alternators outputs by .4 volts to compensate.

Can you monitor the field current to determine the output?
Have you looked up the alternators? Maybe thay have something built in.

 

[Diver300]

I would have an alternator warning light for each alternator.

The warning light connection has its own set of positive diodes, so if the alternator stops working, the main positive diodes will block the voltage, but the light will come on.

You also get an indication that the excitation is working when you turn on the ignition but before the engine is started. The warning lights should light.

You must have a warning light that uses at leasts 2 W. If you are using an LED or something smaller than 2W, put a 47 ohm 5 W resistor in parallel with the warning light.

 

[unclejed613]

My brother posed a question to me tonight as he was taking a break from replacing both batteries and alternators in his truck. According to the shop, one alternator died a while back and the other kept ticking. Now either one of the batteries failed or started to failed and overloaded the remaining alternator and then the engine overloaded the batteries. So both alternators are shot as well as the batteries.

Fool me once, shame on me. Ain't going to fool me twice.

The question posed is how can he tell if one of the alternators fails? Both alternators are literally directly connected to the battery (alt 1+ to battery + and alt2 + to battery +, and both batteries in parallel). And yes this is a big truck, F350 7.xL diesel.

The shop says to install an ammeter, but they are forgetting they are 150A alternators, which means two shunts and two meters. Twice the wiring and stuff to futz with.

My thought was to place a large diode between each alternator and the battery that would then allow a voltmeter or light to be installed (between alt. and diode) to indicate it was functioning. What do you all think?

after re-reading your post i found my previous comments were off the mark since you're talking a parallel system..... a diode will drop an additional 0.7V, which will reduce the charge voltage to the batteries. plus, such high current diodes aren't cheap.

 

[tcmtech]

Keep in mind that I'm looking to isolate the two alternators from each other not the two batteries. Presently all four positive terminals are connected (A1-A2-B1-B2) together. I would lke to isolate the alternator outputs from each other; not to prevent backfeeding directly, but to be able to detect when one has died (ditection is not possible with a voltmeter because of the backfeeding). As mentioned originally, the FMEA of the situation is that one alternator dies but you don't know it until the battery is at a weak point (perhaps after starting on a cold morning) and hit it with a large load (turning on all the lights and high beams) at which time you overload and kill the second alternator, then with no charging system you overload and harm and kill the batteries. The root cause is one alternator died and you had no idea it had happened.

To me this sounds like needless worry and what if thinking for a problem that doesn't really exist. There is no logical reason to isolate the outputs of the two alternators with diodes in the first place being that alternators initially produce three phase alternating current that gets ran through a set of rectifier diodes to turn it into DC power that the vehicles electrical system works on. The reverse power flow blocking function is already built into them.

There are a few million Ford diesel vehicles that run single 100 amp or less alternators for dual battery sets without problems relating to burning out alternators so concerning yourself over a odd coincidence of two battery's and two alternators going out in short succession of each other is needless worry in my view.

My concern comes from why does the F350 have dual alternators on it any way? What is the excessive electrical load that justifies them? Normally a dual alternator setup is only required fore fire and rescue or ambulance type vehicle applications. After that the reasons for having them drastically drops off.

Is there an electrically lifted dump box, snow plow attachment, winch, or some other electric device that draws hundreds of amps for extended periods that puts regular high loads on the electrical system?

 

[4pyros]

My concern comes from why does the F350 have dual alternators on it any way? What is the excessive electrical load that justifies them? Normally a dual alternator setup is only required fore fire and rescue or ambulance type vehicle applications. After that the reasons for having them drastically drops off.

How about a sound system?