DIY 280A Lifepo4 Lithium in 2019 Roadtrek

[booster]

I wonder if it would be good to Gallen's questions and answers into a separate thread where it can get full attention and not mix with this discussion? It will also be easier for people to find in the future if searching similar issues.

[larrylwill]

Originally Posted by Winston

An interesting alternative for Larry to consider . . . but this raises the question why is the 2nd alternator there? By that we mean, what is it connected to that may be impacted by a change in 2nd alternator operation?

For us the 2nd alternator was added for the sole purpose of charging a stand-alone lithium system. Not sure whether Larry has that flexibility . . .

Winston: The 2nd alternator was added because I wanted the voltstart feature and to be able for a fast charge if the battery got low in the night.

I see you have a 2nd alternator. I found out that my alternator wont turn on without a load on its output. The Renogy seems to not be enough. I connected an AGM to the alternator output and now it works. Is yours the same?

I now need an Idea how to get the alternator to turn on without hanging a AGM on it, otherwise as the AGM charges up the resistance goes down and the current drops. Also when off the agm draws current from the lithium until the voltage is balanced.













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[booster]

Originally Posted by larrylwill

Winston: The 2nd alternator was added because I wanted the voltstart feature and to be able for a fast charge if the battery got low in the night.

I see you have a 2nd alternator. I found out that my alternator wont turn on without a load on its output. The Renogy seems to not be enough. I connected an AGM to the alternator output and now it works. Is yours the same?

I now need an Idea how to get the alternator to turn on without hanging a AGM on it, otherwise as the AGM charges up the resistance goes down and the current drops. Also when off the agm draws current from the lithium until the voltage is balanced.


The alternator does not need a load on it to start, but it does need a battery with some real amount of size. Loads and batteries not the same thing to the alternator, Renogy, shore power charger, etc and all modern ones need to see a battery to activate unless they are a power supply type like PD.

[larrylwill]

Originally Posted by booster

I now need an Idea how to get the alternator to turn on without hanging a AGM on it, otherwise as the AGM charges up the resistance goes down and the current drops. Also when off the agm draws current from the lithium until the voltage is balanced.

I connected an AGM to the alternator Input.
The alternator does not need a load on it to start, but it does need a battery with some real amount of size. Loads and batteries not the same thing to the alternator, Renogy, shore power charger, etc and all modern ones need to see a battery to activate unless they are a power supply type like PD.

I was referring
to a Battery load. Like an AGM.

[markopolo]

Originally Posted by larrylwill

................ Also when off the agm draws current from the lithium until the voltage is balanced........

There shouldn't be reverse current through the Renogy unit assuming that the AGM is on the Renogy input and the Lithium battery is on the Renogy output. Are you seeing that or just thinking that could happen? If it's actually happening, contact Renogy tech support to find out what they say about it.

[larrylwill]

If I hook the alternator up to the input of the renogy and the AGM, your right that wouldn't happen. The way its wired is the ground is chassis. The B+ line goes to the DC2DC input, Alternator, inverter, and the rest of the loads and my stand alone charger.
The bottom one is now, the top is with the agm. Is this what you have.

[SteveJ]

Originally Posted by markopolo

It would be better to not use the isolator when switching to a DC-DC unit. Alternately, it could remain in place but be bypassed by moving the chassis & house lugs to the alternator terminal on the isolator. There might be other wires that you need to know what they do. GM vans from that period had a voltage sense wire for example. A voltage sense wire would have to be moved also as it makes the alternator to compensate for the isolator caused voltage drop.

A DC-DC unit will draw from the chassis battery when/if the alternator can't keep up with load when hot and at idle for example. Some units have voltage triggers that should avoid that. Voltage sensing can be added to a Renogy -> https://www.classbforum.com/forums/f...way-11572.html

I eliminated the diode isolator(installed a BlueSea ACR-SI) and simply capped the sense wire. Apparently the regulator picks up a voltage reading elsewhere as it runs a pretty steady 14.2 to 14.35 on a voltmeter. This on a '97 Chevy P30 chassis.

[markopolo]

Originally Posted by larrylwill

If I hook the alternator up to the input of the renogy and the AGM, your right that wouldn't happen. The way its wired is the ground is chassis. The B+ line goes to the DC2DC input, Alternator, inverter, and the rest of the loads and my stand alone charger.
The bottom one is now, the top is with the agm. Is this what you have.

"batt,new" looks correct to me. The DC2DC shouldn't let current drain back into the AGM from the Lifepo4.

[larrylwill]

This is propbly what I will do, also maybe wire it to the fridge.

[Winston]

Originally Posted by larrylwill

I see you have a 2nd alternator. I found out that my alternator wont turn on without a load on its output. The Renogy seems to not be enough. I connected an AGM to the alternator output and now it works. Is yours the same?

Larry, we elected to completely isolate our lithium "house" system from the stock van electrical system and, thus, the last thing we wanted to do was to reintroduce AGM/lead-acid technology to the "house buss" that was designed to be independent from lead-acid and to operate at lithium 'settings'.

So, to answer your question, no, our 2nd alternator is not connected to an AGM, but it is continuously connected to the lithium batteries and all the other electronics, both chargers and loads, that are part of our house system. Our 2nd alternator/Balmar regulator 'sense wire' is connected to this buss so it continuously 'sees' a voltage (except for either a circuit breaker or BMS 'trigger' which, of course, opens the circuit between the 2nd alternator and lithium battery [and DC loads]). Presumably your 2nd alternator regulator has a sense connection (either internally or otherwise) that should 'signal' the alternator to charge/supply power to whatever battery and/or loads you have connected. Frankly, we're puzzled by your need to add an AGM to 'get things going'.

One related comment on 'attaching an AGM' to a lithium system. Several have done this, as we understand it, to provide a continuing load on the 2nd alternator in the event of a BMS or circuit breaker event to thereby minimize the possible 2nd alternator voltage spike which would likely occur when suddenly removing all loads from the 2nd alternator. We've pondered this issue and have correspondingly placed our 2nd alternator sense wire on the alternator side of the BMS 'contactor' and series circuit breaker in the expectation that, at the very least, the 2nd alternator will lose it's "field excitation" quickly upon a BMS/circuit breaker event. Whether this will lower the energy in the associated 2nd alternator's transient 'spike' is questionable but, so far, in 5 years, we haven't had a problem.

[Winston]

Larry, we're a bit confused by your drawings in post #66. We see an "Alt" and an "AGM" . . . . are these the standard vehicle alternator and standard vehicle starting battery? Where is the 2nd alternator and, you spoke of adding an AGM . . . we assumed you were adding an AGM in addition to the standard vehicle starting battery. Did we misunderstand? We expected to see two alternators and two AGMs . . .

[larrylwill]

I think if I bought a Balmar I could eliminate that problem. I have checked several times. If the alternator is connected to the Lifepo4 batteries it works but starts out with 280 amps and in a few minuets drops to around 150A then lower. If I connect it to the BMS it doesn't put out anything. If I connect it to the DC2DC it wont put out anything there either, so I need something to start it. I called nations starter and they told me its internally regulated and needs some kind of a load in order to put out voltage/current. That makes sense to me. If I remember correct connecting a AGM to the + load/ charger line it also works, which doesn't make sense, but I cant verify it for a few days, I had a bone spur removed and iI have a broken wing.

[larrylwill]

Originally Posted by Winston

Larry, we're a bit confused by your drawings in post #66. We see an "Alt" and an "AGM" . . . . are these the standard vehicle alternator and standard vehicle starting battery? Where is the 2nd alternator and, you spoke of adding an AGM . . . we assumed you were adding an AGM in addition to the standard vehicle starting battery. Did we misunderstand? We expected to see two alternators and two AGMs . . .

This is ONLY the 2nd alternator. The original alternator is only going to the starter / vehicle battery. Their 2 separate systems.

[markopolo]

The challenge here as Larry stated is that the 150A BMS goes offline because the output from the 280A alternator exceeds what the BMS is intended to handle.

I think he opted to try using a 60A DC-DC unit as perhaps a temporary solution to get things operational and reliable. The DC-DC unit needs a battery on the input and another battery on the output. That's why the AGM is needed.

Adding the Balmar and turning down the current a bit was one solution. It is a great idea but not likely not enough alternator output to simultaneously charge the discharged lithium and power the air conditioner for overnight air conditioning. That desire was posted here: https://www.classbforum.com/forums/f...tml#post134639

200A+ charging capability is probably what would be needed to be able to rely on Voltstart to both recharge a discharged lithium battery and continue to run the air conditioner and avoid the "death spiral" of ever dwindling remaining capacity mentioned on this forum.

An additional parallel BMS or a higher capacity BMS would be needed to handle output from the 280A auxiliary alternator. Then the DC-DC unit might be able to be used on the OEM alternator in conjunction with the auxiliary alternator. The potential combined output might be 55A from the DC-DC unit and 165A from auxiliary alternator to provide over 200A IF things all work nicely together ..................

[Winston]

Originally Posted by larrylwill

I called nations starter and they told me its internally regulated and needs some kind of a load in order to put out voltage/current.

Thanks for the clarification on your drawings . . . it now all makes sense.

This may seem like a 'technical nuance', but we think Nations means that the regulator requires some kind of 'reference voltage' to operate. A battery, AGM or otherwise, is, of course, such a reference. In electrical parlance . . . "load" generally implies something that 'sinks' current, draws power and, in the absence of being attached to a power source, does nothing. The point being that we doubt the 2nd alternator will work with a regular 'load' as its only connection - - it needs that reference voltage. With this understanding, we understand why your 2nd alternator does not operate when connected to the input of the DC2DC converter as, we're assuming, there is no voltage at that input other than what you supply and, of course, until your 2nd alternator 'fires up', you're supplying nothing.

The good news is that you can jury-rig a small 'kick-start' circuit to provide the comparatively lower current starter voltage necessary to get the alternator operating. A simple momentary push-button switch between the DC2DC input and output - - likely with an appropriate 2nd alternator field winding current limiting resistor in series - - would be a simple fix. Or, use your AGM battery or other (small 12volt battery), again, with a momentary push-button. Once operational, the battery need not remain in the circuit, your 2nd alternator will, at that point, be supplying the voltage reference required for the alternator to continue operating and supplying power to the DC2DC converter.

[avanti]

I assume when we say "reference voltage", what we are really talking about is a current source capable of being used by the alternator to excite the field coils to provide the magnetic field necessary to start generating. Once that has been accomplished, it can use its own power to maintain the field.

This is the difference between a normal alternator and a magneto, which contains permanent magnets and doesn't need such a reference voltage. That is why many motorcycles can be run without batteries.

[booster]

Originally Posted by avanti

I assume when we say "reference voltage", what we are really talking about is a current source capable of being used by the alternator to excite the field coils to provide the magnetic field necessary to start generating. Once that has been accomplished, it can use its own power to maintain the field.

This is the difference between a normal alternator and a magneto, which contains permanent magnets and doesn't need such a reference voltage. That is why many motorcycles can be run without batteries.

I think what Winston was talking about is that alternators need to see a true reference of voltage because the internal regulator needs that reference. It may also need some capacity to absorb output to help hold the voltage correctly as conditions change. Alternators that keep running when the battery is disconnected will go way high even if there isn't a big load dropping spike, even if there is some kind of load to use the output.


For Marko. To be able to charge batteries and also run other stuff simultaneously, the OP would likely be better off with one of these split charge relays that will send 90 amps each direction. He could then ditch the B to B and hook up to this, but would probably still have the same reference issues.


https://www.mastervolt.com/products/...e-mate-pro-90/


A reference Balmer and one of the above would give both, but as Winston mentioned, unknown if a spike would get through or not on a big load disconnect.

[avanti]

Originally Posted by booster

I think what Winston was talking about is that alternators need to see a true reference of voltage because the internal regulator needs that reference.

Sure, but isn't an external excitation current in the field coils a prerequisite to even getting the alternator started?

[booster]

Originally Posted by avanti

Sure, but isn't an external excitation current in the field coils a prerequisite to even getting the alternator started?

As far as I know, yes, you need some current to the field. That current is fed through and controlled by the regulator which on many including Balmars won't let any current through if they don't have the the reference voltage.



I am pretty sure when you take your alternator in to be tested, they hook it up to a load pile and put 12v straight to field, unregulated and see what the get for voltage and amperage. I think 17+v is typical, but not certain.


It is probably more accurate to say the a REGULATED alternator needs a reference voltage and some amperage capacity to run, be it internal like the OP or external like many of use have.

[Winston]

Originally Posted by avanti

I assume when we say "reference voltage", what we are really talking about is a current source capable of being used by the alternator to excite the field coils to provide the magnetic field necessary to start generating. Once that has been accomplished, it can use its own power to maintain the field.

Yes, exactly. This is not a trivial current, but it is for only a momentary period. We actually plotted the field current verses output of our Nations 280amp alternator . . . so have some targets available if someone wants to try it.