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aawara avatar image
aawara asked

BMS 12-200 for Alternator Charging

I am putting together a12V/1200Ah power system for my RV using following major Victron components:

6 x 200Ah Smart Lithium batteries

3K Multiplus

Lynx Smart BMS

Lynx Distributor

Cerbo GX

Smart Solar MPPT

Smart Battery Protect

I am trying to select the best “initial” solution for alternator charging from the 220A alternator in my 2023 Promaster van and am considering using BMS 12-200 for this purpose and have reviewed the technical information on this product from your web site. I have several questions and would appreciate some assistance:

Will the BMS 12-200 be suitable for my battery capacity? I would plan to use it with a 125A fuse for a 100amp charging current.

Does the BMS 12-200 have the necessary charging algorithm for the lithium batteries?

Can it continue to stay in the circuit after possible addition of a second alternator with a Wakespeed WS500 for additional charging current?

Can two 12-200s be connected in parallel? If yes, what total charging current can be expected?


One of the issues I am having with my configuration is that the total charging current from solar, shore power and alternator combined could exceed 400amps or more if two alternators are used. I was planning on connecting the batteries through an ANL fuse and a single battery switch to the Lynx Smart BMS. Each battery can be wired for the recommended 100A charging current. With 6 batteries in parallel, even a total charging current exceeding 400amps should not be a problem. However, the battery switch is rated only for 275amps which would limit the total charging current to 275amps.


Considering the above, I would like to investigate the possibility of splitting the battery bank into two 600Ah banks, each with its own ANL fuse and a battery switch before combining and connecting to the Lynx BMS. Would you recommend this approach, and if so, can two 12-200s be used such that each feeds its individual battery bank? Would the charging current from the Multiplus and the MPPT, routed through the Lynx Distributor and the Lynx BMS be equally split between the two banks?

battery chargingalternator
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klim8skeptic avatar image klim8skeptic ♦ commented ·
@Aawara Thought about going the 24v route? Skipping charging from the RV alternator and putting the effort into a Wakespeed regulator and 24v alternator?


DC cabling at half the copper cost. More options for fusing and breakers. Cheaper mppts. More battery options (3 x 24v-200Ah, 4 x 12v-300Ah, 4 x 12v-330Ah). Easier battery cabling.


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pwfarnell avatar image pwfarnell klim8skeptic ♦ commented ·

If you have a Lynx BMS then you can not run the BMS 12-200 properly because the batteries will be connected to the the Lynx BMS. Have a search around the site, some people have investigated using the BMS 12-200 unconnected just to get the alternator current limiting but I have no idea how successful they have been or exactly how it will work. The other option is battery to battery chargers. If you are planning a WS500 then this integrates extremely well with the Lynx BMS which then fully controls alternator charging.

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aawara avatar image aawara pwfarnell commented ·
After looking at both 12/100 and 12/200, and considering that I will have a Lynx distributor, I think 12/100 is a better choice. The potential conflict with the Lynx BMS is a valid point and needs to be investigated. I am hoping that where there is a conflict, as with charge control or load control, using the Lynx BMS rather than the 12/100 would work. Would appreciate any pointers to sources that cover this situation.
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aawara avatar image aawara klim8skeptic ♦ commented ·

Klim8skeptic, for all the good reasons you list, the original design was based on a 24V system, however it died at the threshold of alternator charging - not enough choice of components & overall additional cost negating the cost savings. I wish that weren't so.

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Mike Dorsett avatar image Mike Dorsett commented ·
Alternative if stuck on 12v would be to skip the lynx bms, and just use the Smart BMS200.


Better to go the 24V route (or 48) Prefer 12V as a lot of led lights are 12-24V operating. Efficiencies are higher at 24v and copper costs are 1/4 (or less).


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aawara avatar image aawara Mike Dorsett commented ·
Mike, please see my comments above.
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pwfarnell answered ·

One caution with the BMS 12/200 is that it does not work well with modern vehicle alternators if they are so called smart alternators which spend a lot of time running at lower voltage and will not charge a lithium. The BMS 12-200 does not include voltage boost circuits. If you have a smart alternator then you need a DC to DC charger or go down the WS500 route.

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aawara avatar image aawara commented ·
I have become aware of this issue which supports the decision to start with an economical solution with a 12/100 over the alternatives I was looking at with CTEK or Sterling products. It might be possible to add a Victron 12-50 DC to DC charger to add to the charging current by taking current directly from the starter battery.

The basic intent with this approach is to have some alternator charging initially. This is intended to be a 'full-timing' RV and I would like to collect some data on power usage and off-grid charging needs before adding a second alternator. The design will be implemented in anticipation of this addition in the future.

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