question

Ryan Turner avatar image
Ryan Turner asked

Mixing AGM and Lithium

Hello Victron Community,

This is my first post and I'm sure there will be more to come. I've just started a new role in a local boat builders and have been tasked with installing the power distribution system.

While planning it out I had found a few design problems and resolved a couple but have been racking my brain how to over come all of them.


The boat will have two engines with two alternators and separate AGM start batteries. (One for each engine). The client wants to be able to charge these when hooked up to shore power so we have two 12/17 victron chargers to be installed to each AGM battery.

The start batteries will then go to two Smart BMS 12-200s (one for each battery) and then go the victron smart lithium bank (2 x 12V 330ah).

Another leg of shore power will go into the multiplus II 3000 and run all the AC loads and the DC side obviously back to the lithium bank.

I know the Smart BMS does not let current back from the lithium to the starter but when the 12/17 chargers for the start batteries hit 13V, it's going to act like the alternator has kicked in and link the two battery banks being charged by the multiplus and the two 12/17 chargers.

Is this a concern and what problems would I expect to see? I hope I've made some sense and not said anything too stupid.

My first though was to use a 120v NC relay on the remote on/off of the smart BMS to open when 120V was detected on the chargers if it was to cause an issue.

battery chargingLithium BatterychargerSmartShuntAGM Battery
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2 Answers
kevgermany avatar image
kevgermany answered ·

It's not a problem. You don't need the relay. Just make sure the battery settings are the same on the Orions and multi. You might want to use the isolated versions of the Orions

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Ryan Turner avatar image Ryan Turner commented ·

There are no Orion's in the system. The chargers for the AGM start batteries are the 120v to 12 V Blue Smart Chargers. Under engine running conditions, the AGMs will charge from the alternator but when connected to shore power, they would charge from blue smart chargers. These would have to be set for AGM settings right? And the multi will be set to lithium charging parameters which I think will be an issue?

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Sarah avatar image
Sarah answered ·

Hi @Ryan Turner A bit of a complex config going on.

A couple of points.

- the starter batteries don’t need to be charged all the time - in fact probably best not to as the charger will spend most of its time in float. A weekly top up is sufficient. A house to Orion to Argofet to each battery is ideal for this solution. You can use the relay on a Cerbo to switch this on for two hours each week. It will keep the batteries happily charged at 13.9 volts (or whatever you select) with an occasional ‘tickle’ to keep them happy. There are other alternatives you can do with a trickle charger.

- unless the alternators are regulated lthe output voltage can be all over the place. If you have an 80 amp regulator I suggest using an Orion 12/12 30 for each alternator. alternator — Argofet and then one leg to the starter battery and another connected to an Orion which is managed from a BMS ATC signal. The Argofet isolates the Orion from the starter battery - this is relevant when you are doing the starter battery top up charge. As the alternator gets hot it should reduce its output to about 50% capacity (again depends on alternator). If you use isolated Orions you can put a shunt on the dc output negative to measure the combined charging current.

For a boat this size (well I don’t really know how big but you have two engines so it’s not a dinghy) I would suggest a Lynx smart BMS this allows you to use DVCC to manage the multiplus and any mppt controllers. In addition to the ATC signal which you connect to the Orions you can use the ATD signal to connect to a battery protect to disable the loads. The Smart BMS also has a slow start feature which is good for the Multiplus. This requires you to use victron smart lithium batteries. By using Lynx bus bars you can seperate the multiplus, charging circuits and load quite nicely. You can also put another shunt on the load circuit to give you accurate DC power consumption.

A solar panel or two is always good for keeping the house batteries charged.

Last comment - a lot of people do mix agm and lithium batteries without issue. Would I? No (especially on a client install unless they specifically requested it).

I hope this helps.

EDIT: I have added the schematic diamondb.pdfdiagram.


Sarah


diamondb.pdf (898.2 KiB)
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Ryan Turner avatar image Ryan Turner commented ·
Thanks for adding the schematic, this makes complete sense.


I think the only drawback of our system would be only having 60amps available to charge from the DC-DC chargers, hence using the smart BMS 12-200s not as a BMS but simply a current limiter by the looks of it.


However you would only need 4 of these to be using the alternators at 50ish % so that might be an option.


I also like the idea of scrapping the two battery chargers and doing one more DC/DC and an Argofet.

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Sarah avatar image Sarah Ryan Turner commented ·
Hi @Ryan Turner I am glad the schematic helped. It’s been sitting in my list of jobs to update. In addition to parallel Orions there is also the option of a 50 amp BuckBoost charger. Some time next year it is also rumoured that there will be a new Smart Orion on the market - if it were DVCC capable it would be worth waiting for. Other options that I have considered are putting a secondary Balmar alternator on the engines with external WakeSpeed regulator that can be controlled over the CanBus using DVCC.
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Ryan Turner avatar image Ryan Turner commented ·

Hello Sarah,


Thank you for your reply, I should clear up some details first. The engines are two Yamaha 450hp engines. Alternator output is 96 Amps (each). You were right in assuming they are not small! I have inherited this system somewhat.


We do have a lynx smart BMS system in place already (in place as in the parts are here). The two victron smart lithium batteries are hooked up to a lynx distribution bus on one side. Then the BMS, then we have another distribution bar with 24 hour power (bilge pumps, multiplus etc).

I have then used a remote battery switch in series to another lynx distribution bar for all other house supplies so they can be isolated remotely when the boat is sitting there. (Non essentials like certain lights)

I really like the idea of using the house Orion argofet layout. I've not used the argofet before and have just done some reading on it. That means when the shore power is connected through the multiplus, the multiplus will charge the lithium bank and then the Orion can be set for an AGM charging profile, through the argofet and charge the starters while keeping both banks isolated. (I'm saying outloud)

Also love the capability to programme the relay on the cerbo.

Surely this is the solution at this point?

My concern with charging the lithiums straight from the alternator. The current is limited through the smart BMS 12/200 which if I understand correctly is just a current limiter, battery combiner and battery protector so there will be no voltage regulation in place. I think the original concern was the Orion wouldn't be enough charge at 30Amps. (Even 60amps with two).

Am I making sense as I have a habit of confusing things!

I cannot thank you enough for all your help so far! Very kind of you to take time out of your day.

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Sarah avatar image Sarah Ryan Turner commented ·

Hi @Ryan Turner ,

Great to hear the info has been useful. Charging Lithium’s from alternators is not what we would like it yo be - yet.

Firstly, with regard to your design each system should only have one BMS (you could put a jumper cable across the BMS terminals but then it wouldn’t be a BMS anymore).

When charging from a ‘stock/unregulated’ alternator the main things to consider are;

- regulating the output current so that you don’t cook your alternator (typically limiting to 50 % of rated alternator output). Some alternators have inbuilt temperature based regulation but a lot don’t.

- regulating the output voltage using a multi-stage charge profile. The Orions aren’t perfect but they are better than nothing (hopefully a new smart Orion that is in the pipeline fixes these limitations).

- for lithiums you want to use the ATC from the Lynx BMS to gracefully turn off the charges if there is an issue.

- if you want more current you can run multiple Orions in parallel.

I’ll try and find a diagram.

S.


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Ryan Turner avatar image Ryan Turner Sarah commented ·
One last question (I'm really sorry!) before I put these changes forward, I don't get the requirement for your other isolators if you are using DC DC chargers from your alternator to you house bank? Does the DC-DC charger not provide this isolation?
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Sarah avatar image Sarah Ryan Turner commented ·

@Ryan Turner - good question. The isolators prevent the Orions from ‘seeing’ the engine batteries. Normally this would not be a problem except for when the engine batteries are getting their weekly charge which would otherwise activate the Orions. There are other ways to do this - this way works well and the isolators were already there from the old AGM batteries ;-)

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Ryan Turner avatar image Ryan Turner Sarah commented ·

I've left my drawings at work so I've quickly sketched out a hybrid schematic/wiring diagram of the inherited system.

(The initial design had the whole perpetual thing going on as the AC feeds for the two battery chargers were on the inverter side) I have now split that bus so shore power feeds it before but here is the rest of it I'm trying to make sense of.

img-20231027-060155.jpg

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img-20231027-060155.jpg (3.0 MiB)