Controlling an Alternator via SBMS0

[PeterBC]

I've discovered that our Alternator is connected to a SurePower 1202 Battery 'Isolator', that directs current to either the Engine Batteries or to the "House" batteries (now a 8Sx3P Lishen 272AH set). As such it needs to be controlled by the SBMS0.

I dont know what algorithm the 1202 uses to direct power, but understand its one or the other batteries.  The Alernator is Bosch exactly like this https://trucks.autodoc.co.uk/bosch/1146265  BOSCH Alternator 28V, 70A Article number: 0 124 555 005  (on a new FPV/Iveco 6 cyl Marine engine). 

Until I can figure out how to control this I am disconnecting the feed from the 1202 to the LiFePO4 batteries, else it could overcharge the set (especially if setting off from a shore power mooring where batteries have been filled overnight). 

I understand you cannot just have a relay or BatteryProtect disconnect alternator output  under load as it can generate significant Voltage spikes and fry the alternator electronics. I am trying to understand how to wire in something to the regulator of this alternator (is it internal or external I'm not sure) to the SBMS0 could disconnect the 'field' current to stop it generating. 

Ideally of course I'd prefer to just direct the alternator back to the starter lead acids to float them... but if I have to turn it off thats fine. I need to know how this 1202 behaves as it may not be appropriate with a LiFEPO4 on one string and Lead Acid on the other ?

Thanks..

[PeterBC]

Could I instead of the SurePower 1202 simply direct connect the Alternator to its engine lead acids, and then via a one way Battery Protect allow current to flow to the LiFePO4 if the SBMS0 allows, which would only happen if the Engine lead acids were over the LiFEPO4 voltages (between 24 and 28.4) which would occur when the Lead Acids  are  full or partially.  If the LiFePO4's were charging and SBMS0 cut off the link, then flows would divert to the engine batteries and no voltage spike should occur.  The Battery Protect is a one way device inherrently preventing any leakage back to the starters.  With my 70A alternator a 100A BP should be sufficient ? 

Is there danger that the LiFePO4's will take most of the out put and leave the engine set poorly charged over time ? Could they overheat the alternator by accepting peak current for long periods more than a Lead Acid would ? 

[Dave McCampbell]

Peter.  Here is a link on our website to how we have handled this issue for many years.  We are now using it with our lithium house bank and SLA engine start battery.  You could get rid of the 1202 if you use this and isolate your house bank from the start battery.    http://www.svsoggypaws.com/electricalsystems.htm#tricklecharging 

[PeterBC]

So after some research I discovered the 1202 is just a diode bridge (capable of 120 amps) allowing both batteries to simultenously draw current (if they need) independent of the other, but no back flows from either battery to the other.  So the solution we went with is to just put the battery protect on the output of the 1202 going to the lithiums, so the BMS can disrupt that if needed. Any voltage 'spike' from disrupting that flow simply pushes instantly any current to the starter which effectively absorbs the transient and balances with the alternator as needed. 
So this is the layout now in place.. (not showing the actual SBMS0 EXTIO that interfaces directly to the BP to do a HVD if needed.) (nor fuses, isolators etc). 
Since the 1202 is new (replaced last yr) before we had the lithiums I felt it easiiest to interface this way.

[Plamen]

Hi Peter, You need a DC-DC battery charger. It will output just the amps it's rated for (CC Constant current source). Alternators (those in car engines if not modified) are constant voltage sources.

That's https://www.youtube.com/watch?v=jgoIocPgOug another way, to control the alternator. 
It's been discussed here in the forum, but as it's not something i need i didn't marked it. Now i can't find that post. Another advantage is that DC-DC chargers (at least some) have remote control so is easely cotrolled by SBMS.

[Oberon Robinson]

Peter, as Plamen said, you need something to limit the current into your lithium batteries. They have very low internal resistance, and will burn out your alternator in no time. Dave's system works because he has a smart alternator controller that limits the output current. Most people use a Victron Orion, Sterling B2B, or Renogy DC-DC charger. Sterling has some good videos on YouTube showing what happens if you directly charge a lithium battery from an alternator.

[PeterBC]

Bummer, it seems the expense and limitations of safely allowing alternator charge may not be worth it for me.  DC-DC 24/24 seem limited in amps (17amps is biggest victron orion it seems) and the larger DC-DC units cost $600 and up it seems even at that. 
The video is illuminating.. and seems that slow speeds are the biggest issue for the alternator as they provide maximum current still being a constant voltage source sort of, but their internal cooling from inbuilt fan is 1/4 as good at 1/2 the rotational speed.  I gather lead acids just never soak the full capacity for long hence avoid burning it out ? Seems stupid that alternators dont limit themselves if overtemp. 
As we prefer to be static more days than cruising,  we will rely on shore power and generator when needed, but are looking to add solar later too. Solar is not very attractive in France summer since we spend time trying to find shade mostly ! 

[PeterBC]

As always more knowledge , raises more questions..
I'm trying to distill the 'issue' of alternators to LFP batteries. I'm clear on the not cutting load without something to absorb the voltage spike (eg a lead acid still across it).  But the 'overheating' issue makes me curious. 
Is it current exceeding rated output due to low internal resistance of LFP ? or is it the tendancy of LFP's to absorb the max current for much longer than a lead acid and few alternators are rated for continuous use at max amps ? One thread I've seen comments that lower idling engines reduce internal cooling of Alternator (eg 1/2 revs is about 1/4 cooling). But why is that issue more for LFP than Lead Acids ?

All the solutions I'm seeing are expensive and/or limiting amps available considerably.  Buck Boost or B2B converters at 50+ amps are expensive. So are temp compensated alternators (eg Balmar) or external regulators and stuff, all of which seem to rely on reducing amps as the alternators are just not capable of max current for long periods ? Is there an alternator that can safely limit its current to whatever its can handle and sustain that at 50amps or more 24v ?

[Jhon]

From what I understand it is because the battery has very low resistance nearly a short circuit and it will take whatever the alternator can produce and the alternator has no limit on the output, it is designed for lead acid.  Heating will happen in the winding of the alternator and when it can not dissipate the heat fast enough it will overheat.

I watched a guy explaining how he could parallel lead acid with LifePo4 and have the LiFePo4 do most of the early heavy lifting with the lead acid doing more when the LiPo4 was nearly empty.  Even if that works (I have no idea if it does or not) I don't think you would want to do that with a small car battery.  I wonder if you'd burn out the starter motor.  My guess is that you want to isolate the two batteries either with a battery to battery charger, a second alternator designed for LiFePo4, or something else.

Again from what I have seen, you can install a second alternator dedicated to charging the house battery, but a more cost effective solution seems to be to get a battery to battery charger.  They should sense when the lead acid vehicle battery is charged and only then turn on the charging for the house battery, as well as limit the current drawn form the alternator.  If the battery to battery charger has a remote on/off the SBMS0 can  control that, or else you can add a relay or potentially a DSSR20.  When you are driving, you will be burning a little more fuel to charge the battery a little, but that might be enough so you do not need to run a generator when you get to your destination.

Again, thinking out loud, please correct me if I am wrong.

[Plamen]

Peter, some time ago i've 'played" with a truck alternator connected to a small generator engine.  https://groups.google.com/g/electrodacus/c/om532PH6JO0/m/xLQlQUmaDwAJ

If you have constant speed of the alternator and if you know what is a safe temperature for the coils than it can be done just with a small DC-DC step down converter. 

[Plamen]

i've hit post message by mistake. I DON'T RECOMMEND it to anyone. We are just talking how it can be done for less money. So if you leave your engine idling you can disconnect the field coil from the original voltage regulator and connect it to the DC-DC converter (i'd disconnect the starter acid battery for that).  Starting from 0 you rise voltage to the coil field. If you have say a 80A rated alternator rise the voltage till it starts to charge with 40A. Chek the alternator temperature every few minutes (it will be better if you can connect a termometer there and can see it all the time).

     It works but is rather a one time life saving solution if you need to charge the battery and only have the alternator. 

[Richard Bewza]

I have an out of the box solution for your Alternator charging problem. I caution you that it is only theoretical. Change your 24 Volt alternator to a 100 amp 48 volt alternator which will probably a charge that 56 volts. 56 x 100 =  5600 watts. It is best not to pull more than 50% rated capacity of an alternator so that gives us approximately 2800 watts of useable power.
Install 2 Victron MPPT charge controllers connected to the new alternator. One 10 amp unit to trickle charge your start batteries and one 100 amp unit to charge your 800 amp bank.

Rick