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Need B2B and alternator recommendation for 12 V RV

LarryJForman

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I am building a 12V system for our 1969 22 ft. classic RV with solar. I have mounted 6 ea. Battle Born GC2 100 Ah batteries connected to an AIMS 3000 watt inverter/charger/transfer switch. I will be removing the vehicle 12 V flooded lead engine/house batteries and using just the LFP for all RV power and starting the engine. The current alternator is 37 amps and I have found a 140 amp alternator replacement, but running at about 3000 rpms typically the alternator output might be around 80 amps or so. Much beyond 80 amps and the single alternator V-belt will tend to slip. I definitely do not want to over charge the LFPs or over heat the alternator. What B2B would be recommended? I assume the alternator output only go to the B2B and no where else, since there is only one Lithium 12 volt battery bank. I will be installing 800 watts of solar for additional power. The primary drain when driving will be the 13.5 kBtu RecPro heat pump/AC at about 13 amps of 120 VAC. Any recommendations appreciated.
 
Oops, I just checked with Battle Born and they do NOT recommend using their GC2s for an engine starting battery. So I need to have a small flooded lead acid battery for an engine starting battery. I will check out the Libin 225 next and also check to see if the manufacturer will recommend a maximum alternator load to prevent burning it out.
 
search out BBMS on youtube as an alternative way to get your lead and lithium banks to dance together better.
Tis what I am doing.


My start and aux. bank are 24v lead (aux for winching etc.) and charged via alternator. Via the BBMS my aux bank (with solar charging on that too) will feed the house liPo4 and visa versa via the BBMS. BBMS manages energy to and from a lead and LiPo4 bank.

Went this route to not have to swap alternator system in my military truck that is very atypical and would be very expensive to re-work it all..... nor will it burn up my extremely expensive military alternator.
 
600Ah of lithium will destroy a standard vehicle alternator directly connected. Fit a battery to battery charger between the lead acid starter battery and the house battery. Thankfully you discovered that your lithium batteries cannot replace the LA starter battery.
As you surmise 80 amps from a 140 A alternator is a resionable safe output. Since the vehicle electrics will need power, there is perhaps 50 amps available for the B2B charger.
B2Bs available from, Victron, Sterling Power, Renogy, Voltronic, Kasie, Redarc.
Since you have a very expensive battery bank, having a charge controller that can be user set with charge profiles would seem an advantage.

Mike
 
I really like my victron charger 12|12-18, 230A battery, 140A alternator on a winnebago, dual starting batteries. The app is really slick, and all charging parameters are adjustable. I have mine set to mostly just float since solar tends to keep them up. There's a minimum boost time of like 20 or 30 minutes, which starts over each time you power on the unit - start the engine.

An 18A to 30A output will put a good amount of power back in an average drive-time, say 4 to 6 hours. I wanted something for a string of cloudy/rainy days, or driving at night. You just don't want to over power your alternator. 50A headroom seems like a lot to me, maybe not. All of your vehicle electricals need to power off the starting battery/alternator, so that's wipers, AC blower, lights, radio. You can only use what's leftover for your b2b charger.

If I need a bulk fast charge I have a 55A converter/charger I can plug into shorepower or run the AC generator, which we do for AC anyway.
 
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an outside the box alternative is a BBMS. New concept.... new device. Thus Requires different thought process and wiring. If you dont have lithium yet..... your more than half way there already. A BBMS is maybe best thought as adding a lithium bank as a "reservoir" whose only two jobs is to keep the lead topped up as power is drown from it. (such as at camp/night when little to no solar or alternator is adding charge) and two- when it is time to refill both lead and lithium via some sort of charging..... it manages this so both the lead and the lithium reservoir get refilled. The lithium charge in essences flows THRU the lead and gets managed by BBMS when charging is going. This is how the lithium ends up dancing just fine with old school alternators. The alt. only sees the lead. BBMS does the rest.

hmmm maybe think of the BBMS as the bartender that keeps serving you (lead battery) from the bar cooler (lithium bank) as you consume beer at night at night........ and in the morning bartender (BBMS) manages restocking things..... while treating you (lead battery) for a hangover.
 
Oops, I just checked with Battle Born and they do NOT recommend using their GC2s for an engine starting battery. So I need to have a small flooded lead acid battery for an engine starting battery. I will check out the Libin 225 next and also check to see if the manufacturer will recommend a maximum alternator load to prevent burning it out.
6x battle borns in parallel should be able to safely start your engine. Only one would be insufficient in many cases but 6x parallel can supply 1200Amps for cranking without exceeding battery specs.
 
What is a BBMS? Where can a buy one? Who makes it?

A BMS in part manages the cells within a lithium battery; bringing them together in a tight happy dance. In part manages few other protective things too. A BBMS manages BANKs of Batts like BMS manages cells. BUT.... it is designed specifically to bring two different banks (lead and lithium) together in a tight happy dance.

Made sold by an engineer whom has been living on sailboat for 20yrs and was looking for better way to add lithium to his huge lead system with out having to throw out a big chunk of his batts and existing charging system to do it. search "BBMS Emily and Clark" on youtube.
 
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OK, now understand, it's the lead plus lithium boat guy. From a technical viewpoint it's a pointless exercise unless you are married to a lead battery bank.

The lithium engine starting may be possible but the alternator would immediately come on line and be confronted with a very low impedance battery, my guess is something would melt.

Mike
 
OK, now understand, it's the lead plus lithium boat guy. From a technical viewpoint it's a pointless exercise unless you are married to a lead battery bank.

The lithium engine starting may be possible but the alternator would immediately come on line and be confronted with a very low impedance battery, my guess is something would melt.

Mike
yup on all points. Funnny how you express the married to lead point like it's a "not a have to be thing"......... then show..... you do actually have to be married to it, to keep from melting things.
 
The lithium engine starting may be possible but the alternator would immediately come on line and be confronted with a very low impedance battery, my guess is something would melt.
I have paralleled lithium batt into 12v lead acid system across a large diode. Done that way you can have the lithium feed into the 12v system when that system voltage drops under load, but not have 12v charging go into lithium bank. At 'rest' the ~12.6v lead does not really drain anything from the ~13.4v lithium because of the ~0.7v drop of the diode. I am experimenting with how much lithium charging 'leaks' into lead acid system across diode but it seems to be pretty minor so far. Not appreciably slowing my lithium charging (because even at same voltages lithium has much lower resistance) and not catching my diode on fire either.

Another option if you wanted to use the lithium as the main starting battery is just to reroute starter power cable directly to lithium somehow, but it would require the lithium bank to be chassis grounded already. I think the diode is easier.
 
I have paralleled lithium batt into 12v lead acid system across a large diode. Done that way you can have the lithium feed into the 12v system when that system voltage drops under load, but not have 12v charging go into lithium bank. At 'rest' the ~12.6v lead does not really drain anything from the ~13.4v lithium because of the ~0.7v drop of the diode. I am experimenting with how much lithium charging 'leaks' into lead acid system across diode but it seems to be pretty minor so far. Not appreciably slowing my lithium charging (because even at same voltages lithium has much lower resistance) and not catching my diode on fire either.

Another option if you wanted to use the lithium as the main starting battery is just to reroute starter power cable directly to lithium somehow, but it would require the lithium bank to be chassis grounded already. I think the diode is easier.
cool idea. Though IMHO sorta illogical to not use the alt. to kick the lithium up quickly and be done with it. Granted that is assuming one has a large enough one to do so already.

In my case for example; have approx 140amps left over after draws at 24v after to do just that so it is really illogical to not capitalize on it. Use alt to fill Lithium quickly (with out killing the alt)...... then use on rest of trip the solar dedicated to say HHO and /or Meth-water for improving fuel millage a tad or at least engine life increase. The solar powering of those removes the typical losses in running those type devices since it takes alternator drag out of the equation, making them a potential gain instead of no gain or minor net loss


For others with not large enough alt. it gets damn expensive to try to charge lithium with alternator. In that case IMHO just spend that money on more solar. If your out of space to put the solar.... make folding panels to put out once your at location.... or slide out panels below the ones on the roof. That is likely less costly than upgrading to special alternators etc.
 
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cool idea. Though IMHO sorta illogical to not use the alt. to kick the lithium up quickly and be done with it. Granted that is assuming one has a large enough one to do so already.
I agree, and will do so but haven't 'assembled' that functionality yet even though I have the parts already.

On a factory-built RV it may already do something like what you're talking about between the starter and house batteries. My RV has a large solenoid up front that engages anytime key is on to direct alt charging to house batt. When you turn the key off it disengages at which point those two batteries are isolated from each other unless you press the 'emergency start' switch in the rear. The same functionality would work for the lithium alt-charging connection. You can also use any cheap <$20 solar charge controller's load outputs to run a solenoid, possibly an existing solenoid, off your custom voltage setpoints. At least any SCC that has a screen and buttons..:ROFLMAO:

It still leaves the issue of controlling current such that you don't run the alternator at max load into the lithium bank for long periods (especially at idle, when the rpm-based forced air cooling from the internal fan is weak). I have not tested the alt-charging side of this yet, but i am already feeding my 'shore power' batt chargers through an 80a PWM scc that has a configurable charge current limit (and it does work, i did verify that). I think IF you don't have an alternator that could smoke the 80a controller in the first instant (i hope that is my case), that it would then pwm the output down to <80a average and you could set it to a level that's comfortable for your alternator longevity, with the starter battery alleviating any serious side effects of the 'ripple' of PWM'ing a large current on the alternator output. The PWM scc doesn't need a minimum 'voltage delta' between input and output to function (like an mppt would), but ultimately your actual charge current would depend on that delta to some extent. I.e. i think you can get good flow into lifepo4 with .1v delta, but possibly not anywhere near the alternator's rating. So it still depends on your alternator holding the main 12v system at a voltage at least a couple tenths higher than your lithium is at.

The other gotcha to this idea that i already mentioned, is whether or not your lithium bank is chassis grounded in the vehicle. Mine is, for no good reason, that's just how i initially wired it. The problem there is if you have an SCC where all the positive terminals are internally bridged together, the SCC would have no control/authority because the chassis ground would connect the lead and lithium together, and the common positive in the SCC would connect them together, and the negative-side switching in the SCC would accomplish nothing. The solution would be either NOT have your lithium be chassis grounded, or chassis grounded through another relay only when not being charged . I'm having brain fog over all the possible reasons to have your lithium bank chassis grounded or not, so i'm just throwing those options out there.


My basic plan in my RV is to take the onboard 12v ~40a charger (which puts out 13.9v open circuited), in parallel with a couple of other small ~20a 120v chargers, and put it through my 80a SCC with current limiting, limit it to ~60ish amps, and set 'bulk/absorption' AND float voltage to 13.4. At that point my lithium will charge to 13.4 with no 'leakage' to the lead side until it gets close to 13.4, after which there will be slight 'maintenance/float' charging through diode into the lead acid @~12.7v, of a few amps. Low single digits from what i've seen so far. That's charging from AC. If nothing is pulling from the lead acid batts when parked (because inverter is hooked to the lithiums), that should be sufficient to keep them 'full' at 12.6 by at least fully offsetting whatever small drains there are (internal batt self-drain + some 12v interior lamps maybe), if not actually 'charging' them in the electro-chemical sense. Alternator would do 'actual lead acid charging' when engine was running.

On the DC side there is already a solenoid up front that hooks starter battery (thus alternator) to house battery when key is on. With slight rewiring of the existing cabling in the RV i can parallel lead acid house batt to starter batt permanently, and use that functionality to hook Alt charging to lithium. When key turns off the lithium and lead are disconnected.

The whole diode side of things is entirely optional here. It's just a workaround to 'stealing' the shore charger away from the lead but giving some passive 'floating' on shore power using a diode i already had anyway. The other option is skip the diode entirely and use the load port on the SCC in this scenario to ALSO trigger that same Lead to Lithium relay that turns on with ignition key, to also turn on when lithium his something like 13.4, and turn it off when it hits 13.3, or 13.5 to 13.4, etc. That would make the lithium charger be the 'shore charger' for the lead, but make sure the lithium is full first, and not allow the lithium to discharge into the lead in the event of a fault such as a lead acid batt gets a dead cell, short in the 12v side etc. Downside is, assuming my onboard charger HAD any 3-stage charging and temperature compensation at all, you'd be losing that and it would be 'dumb' lead acid charging unless you stuck another SCC configured for lead acid into THAT line. Part of the extenuating justification for my silly diode (if i even keep it) is the .7v drop means i can leave it 'dumb' with no downside other than it won't actually properly recharge the lead from a real discharge, just prevent it from discharging from small draws when parked.

So really the only thing needed to do this that wasn't already in my RV is the SCC. The wiring from front to back, and the solenoids, already exist.
 
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I agree, and will do so but haven't 'assembled' that functionality yet even though I have the parts already.

On a factory-built RV it may already do something like what you're talking about between the starter and house batteries. My RV has a large solenoid up front that engages anytime key is on to direct alt charging to house batt. When you turn the key off it disengages at which point those two batteries are isolated from each other unless you press the 'emergency start' switch in the rear. The same functionality would work for the lithium alt-charging connection. You can also use any cheap <$20 solar charge controller's load outputs to run a solenoid, possibly an existing solenoid, off your custom voltage setpoints. At least any SCC that has a screen and buttons..:ROFLMAO:

It still leaves the issue of controlling current such that you don't run the alternator at max load into the lithium bank for long periods (especially at idle, when the rpm-based forced air cooling from the internal fan is weak). I have not tried this yet, but i am already feeding my 'shore power' batt chargers through an 80a PWM scc that has a configurable charge current limit (and it does work, i did verify that). I think IF you don't have an alternator that could smoke the 80a controller in the first instant, that it would then pwm the output down to <80a average and you could set it to a level that's comfortable for your alternator longevity, with the starter battery alleviating any serious side effects of the 'ripple' of PWM'ing the alternator output. The PWM scc doesn't need a minimum 'voltage delta' between input and output to function (like an mppt would), but ultimately your actual charge current would depend on that delta to some extent. I.e. i think you can get good flow into lifepo4 with .1v delta, but possibly not anywhere near the alternator's rating. So it still depends on your alternator holding the main 12v system at a voltage at least a couple tenths higher than your lithium is at.

The other gotcha to this idea that i already mentioned, is whether or not your lithium bank is chassis grounded in the vehicle. Mine is, for no good reason, that's just how i initially wired it. The problem there is if you have an SCC where all the positive terminals are internally bridged together, the SCC would have no control/authority because the chassis ground would connect the lead and lithium together, and the common positive in the SCC would connect them together, and the negative-side switching in the SCC would accomplish nothing. The solution would be either NOT have your lithium be chassis grounded, or chassis grounded only when not being charged through another relay. I'm having brain fog over all the possible reasons to have your lithium bank chassis grounded or not, so i'm just throwing those options out there.

But anyway, i do plan to implement exactly what you're suggesting. (y)
keep me posted please on your doings please. My system is 24v including alternator.
 
the BBMS system is a simple concept , essentially connecting a Li bank to a Lead Acid when the voltages are compatible. That's all it does in general ( it has some protection against short cycling )

it’s only really suitable where a big lead bank already exists.
note that it’s not ISO compatible for European boats
 
the BBMS system is a simple concept , essentially connecting a Li bank to a Lead Acid when the voltages are compatible. That's all it does in general ( it has some protection against short cycling )
That's essentially what i'm building out of an SCC and some existing wiring and solenoids. Although i guess my setup accomplishes some other things as well, i guess the 'meat and potatoes' is crude 'BBMS functionality'.
 
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