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Charging 12v AGM, 12v Lithium in a 24v vehicle

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woytovich

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I have a 24v Toyota Land Cruiser Troopy. I am currently running a Victron 24>12 DC-DC charger to charge a 100ah AGM battery. I want to add a 100ah Lithium battery.

Can I swap the Lithium into the position currently occupied by the AGM to be charged by the Victron and add a 12>12 DC-DC smart charger between the Lithium and AGM to charge the AGM? Will this "confuse" the Victron smart functionality regarding the charge state of the Lithium battery?

Is there a better way (short of ditching the AGM battery)?

PS I'll be adding solar input as well down the line.

Newbie here, so be gentle with me please.

Thanks,
Mark
 

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Hi @woytovich

Here are my AGM settings on my Victron 100 | 50

IMG_1470.png

I think that is too high of voltage for most LFP.

However, if your DC2DC charger allows settings, maybe set it to LFP & that will be ok for AGM ,,, not perfect, but ok ?

Have to read the manuals & know the batteries you are using.
 
If none of your charge settings for the AGM go past 14.6 volts you could just directly parallel them together and not install anything in between.
 
Vigo said:
If none of your charge settings for the AGM go past 14.6 volts you could just directly parallel them together and not install anything in between.
Click to expand...

If temperature compensation is also part of the OP’s charger ,,, like my 100 | 50 noted above, it is set @ 14.7v @ 25C 😉 ,,, even a 14.6v set @ 25C can see higher voltages than 14.6 when colder than 25C.

So the OP should be careful & fully understand their system.

Example 15.11v when set on 14.7v when temperature compensated for my AGMs & in cold weather

IMG_1471.jpeg
 
Yes, by paralleling AGM and lifepo4 you are always either A: going to lean on the BMS to disconnect high voltages (probably not a good plan) or B: not be treating your AGM 100% ideally (probably the better choice).

To me it comes down to, if i treat my AGM 80 or 90% of ideal vs 100%, is the slight loss of lifespan worth the cost/effort savings of not having to implement another charge management device? Generally i would say yes. A 100ah AGM is $150-200. Taking a chunk off the lifespan of it means you are missing out on what, $40 of value? Even if your time is free you'd be hard pressed to implement something between for less than that. I'd just accept the compromise, and when the AGM dies you replace it with another lifepo4 and everything is golden. That's the path i personally would take.
 
Vigo said:
Yes, by paralleling AGM and lifepo4 you are always either A: going to lean on the BMS to disconnect high voltages (probably not a good plan) or B: not be treating your AGM 100% ideally (probably the better choice).

To me it comes down to, if i treat my AGM 80 or 90% of ideal vs 100%, is the slight loss of lifespan worth the cost/effort savings of not having to implement another charge management device? Generally i would say yes. A 100ah AGM is $150-200. Taking a chunk off the lifespan of it means you are missing out on what, $40 of value? Even if your time is free you'd be hard pressed to implement something between for less than that. I'd just accept the compromise, and when the AGM dies you replace it with another lifepo4 and everything is golden. That's the path i personally would take.
Click to expand...

Yup “Agreed” ,,, set it to LFP & it might be “Ok for AGMs” per my original post.

IMO, Not all AGMs are that cheap & LFP isn’t the golden answer to every battery situation.

If one has to deal with “cold” regularly 🥶🥶, a good quality AGM might be a better solution.


Thread 'Rolls AGMs “S6-275AGM-RE'
https://diysolarforum.com/threads/rolls-agms-“s6-275agm-re.82288/
 
OP here... FYI I already own a CTEK 12v DC-DC charger. So that's not an obstacle for daisy-chaining Alternator > Victron 24/12 charger > Lithium > CETK 12/12 > AGM (or the other way around)
 
Chargers in question:

ctek-batterychargers.co.za

D250S DUAL | CTEK Battery Chargers

Charge while you drive Battery to battery charger in a dual battery application The D250S DUAL charger obtains its energy from DC sources such as alternators, solar panels or wind power and optimises this power to meet the charging requirements of different battery banks.
ctek-batterychargers.co.za ctek-batterychargers.co.za

Orion-Tr Smart DC-DC Charger Non-Isolated - Victron Energy

The Orion-Tr Smart DC-DC charger is a professional DC to DC adaptive 3-stage charger with built-in Bluetooth. For use in dual battery systems in...
www.victronenergy.com www.victronenergy.com
 
Additionally extreme cold is not likely to be an issue. The battery(ies) and chargers are in the vehicle and would/could be warmed by running the vehicle prior to charging. This is generally a spring/summer/fall use vehicle.
 
Vigo said:
That's the path i personally would take.
Click to expand...
Please clarify: If I were to not do as I have suggested, with 2 charging devices, what arrangement are you proposing? (again: a newbie here)

Would the Victron not be bothered by the parallel addition of an AGM battery when it thinks it's just charging a Lithium?
 
I was proposing to hook them up in parallel (both positives hooked to same thing, both negatives hooked to same thing) and just accepting the minor imperfection of the lithium settings not being 100% ideal for the AGM. But since you already have the DC-DC there is no real cost to doing what you suggested originally, just a bit of wiring and some time.
 
Vigo said:
I was proposing to hook them up in parallel (both positives hooked to same thing, both negatives hooked to same thing) and just accepting the minor imperfection of the lithium settings not being 100% ideal for the AGM. But since you already have the DC-DC there is no real cost to doing what you suggested originally, just a bit of wiring and some time.
Click to expand...
Thank you.
 
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