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How many DC to DC chargers for hands off dual chemistry battery system?


Burgboy
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Looking to add 3 lithium batteries to my lead acid system. One or two dc-dc chargers?

Hello I currently have a set of lead acids charged by solar panels. Im trying to add in a set of lithiums to the array. Does anyone know if dc-dc chargers only work one way? Or perhaps I need two? The idea is to have two different chemistries and be able to charge and use them at the same time without needing to switch manually

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1 minute ago, JDCrow said:

Alternator still charges chassis lead acid. Leads goto a breaker, then to DC/DC and leads from it goto lithium Coach batteries. 

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Do your leads charge the lithiums and lithiums the leads? 

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1 minute ago, Burgboy said:

Do your leads charge the lithiums and lithiums the leads? 

Like bi-directional? No they don’t one way only, DC/DC alternator to lithium. I have a new inverter/charger that sends out 4 amps trickle charge to chassis  lead acid when plugged in to shore power. 
 

The big boy combiner is gone. I use a jump box if the chassis batters ever lose charge 

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17 minutes ago, Burgboy said:

So sounds like the victron unit will need one in each direction to do what I need it to do. Thanks! I plan on having 4 lead size 27 and 3 size 27 lithiums

You’re wanting your lithium to charge your lead? 

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Just now, JDCrow said:

You’re wanting your lithium to charge your lead? 

I want them to keep eachother at optimal levels and both be available to be used as housr batteries without needing a switch. That way I can have the alternator and generator charging the leads as standard. And i will have 2 mppt solar chargers going to each set of chemistry

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Two items of caution.

Make sure you understand not only the pro’s of the Lead + Lithium power bank - but also the con’s. And how to spot the issues as they arrive. 
 

Also if you have two DC-Dc chargers going in opposite directions- make sure you have the charging allowed set-up correctly. 
 

What can happen if both are running at the same time is you will lose 13% of the power on both sides as you make a loop - and with both being on - it just keeps going. If they both just run off of voltage when the house gets to the turn on level (because of solar), it starts charging the chassis, then a bit later the chassis gets to turn on level and suddenly you have a loop that is just draining away power. 
 

On the chassis side you probably need to run the wire turn-on switch through a relay that connects to the ignition - that way you don’t have the loop. 
 

There is an interesting YouTube on a sailboat that is using the Lead+Lithium battery bank. 
 

I found it interesting- but I am not going to do it. 

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2 minutes ago, Rocketman3 said:

Two items of caution.

Make sure you understand not only the pro’s of the Lead + Lithium power bank - but also the con’s. And how to spot the issues as they arrive. 
 

Also if you have two DC-Dc chargers going in opposite directions- make sure you have the charging allowed set-up correctly. 
 

What can happen if both are running at the same time is you will lose 13% of the power on both sides as you make a loop - and with both being on - it just keeps going. If they both just run off of voltage when the house gets to the turn on level (because of solar), it starts charging the chassis, then a bit later the chassis gets to turn on level and suddenly you have a loop that is just draining away power. 
 

On the chassis side you probably need to run the wire turn-on switch through a relay that connects to the ignition - that way you don’t have the loop. 
 

Thank you, this is what I need to hear. So one of these switches is absolutely required then?

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So want the generator to charge the lithium through the inverter then the lithium go through a DC/DC back to the lead. Interesting but like mentioned above, the charge patterns, which I’m sure you’ve looked into, are not the same going up as down. I don’t have my coach with me, but the DC/DC is Bluetooth and you can select the modes but can’t remember if it would go lithium to lead. I’m sure there is info out there. 

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No.  The switch I was talking about is the little wire loop on the bottom left side of the Victron DC-Dc charger. If the wire is not connected then the Dc-Dc charger does not run. So if you run it through a relay that is driven by the ignition wire, then the only time the chassis battery can try to charge the house battery is when the ignition is on (and thus the alternator is running).

Look closely in the Install manual and it talks about it. 
 

FYI - you will still have the loop when the alternator is charging- the alternator is producing 14.3v - so the (other) Dc-Dc charger starts to charge the house batteries - when the house batteries get to the turn on voltage they start charging the chassis batteries, and thus you have the loop that is draining power at 13% each. But in this case the alternator is a large enough power source it can handle it. 

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1 minute ago, JDCrow said:

So want the generator to charge the lithium through the inverter then the lithium go through a DC/DC back to the lead. Interesting but like mentioned above, the charge patterns, which I’m sure you’ve looked into, are not the same going up as down. I don’t have my coach with me, but the DC/DC is Bluetooth and you can select the modes but can’t remember if it would go lithium to lead. I’m sure there is info out there. 

No. I know about the charge patterns. 

I want

Lead takes all the ICE power plus a solar charge controller

Lead to DC - dc charger to lithium which also has its own solar charge controller.

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I believe what the original poster is doing on the batteries is making a Lead+ Lithium hybrid battery pack - connecting 2 lead batteries parallel with 3 lithium batteries into one large house bank. 
 

There seem to be some pro’s - but…

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4 minutes ago, Rocketman3 said:

I believe what the original poster is doing on the batteries is making a Lead+ Lithium hybrid battery pack - connecting 2 lead batteries parallel with 3 lithium batteries into one large house bank. 
 

There seem to be some pro’s - but…

Well the pros in my mind are having the lithiums hardly cycled. And kept as a dense backup to the 2-3 year cycle life however cheaper per unit leads. 

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28 minutes ago, Burgboy said:

Well the pros in my mind are having the lithiums hardly cycled. And kept as a dense backup to the 2-3 year cycle life however cheaper per unit leads. 

Over my head, I’ll have to read up. With 3000-5000+ cycles on a lithium I can see why they go 10+ years, so I’ll read up to get it to make sense to my dense noggin. 

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  • 1 month later...

I'm late to the party, but why are you building a acid/lithium system?  Are the lead acid new enough you want to hold on to them? Plus an extra solar charge controller and a DC to DC charger--that's almost another lithium battery cost (depending on brand)  I have older lead batteries and waiting for them to give up, then will change out to a complete house lithium system.

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