Smart BMS 12/100 low charge rate

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luke4140 asked Sep 12, '22

Smart BMS 12/100 low charge rate

I have a victron lifepo4 90ah battery connected to my smart bms 12/100 and a smart victron shunt. I am using the bms to charge the house battery from the vehicle alternator. The vehicle has a temperature controlled alternator (new hilux) I have fitted 2 x 30amp fuses and set the bms to charge 40amps. This is a new set up and the most charge I can see from the shunt is 12amps when the engine is cold, and drops down to 5amps when hot. The house battery is at 40%. Why can I not get any more charge ? My friend has same car and enerdrive dcdc and he can get 40amps. I have triple checked wiring and all is good.

thanks Luke

battery charging BMS alternator

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ell249 commented · Sep 28, 2022 at 12:55 PM

Hi Luke - heads up I'm not a pro, unfortunately just someone with the same/similar issue.

But first thing might be to check your cable size and connections are clean/sufficient. Particularly if the Smart BMS is mounted away from the car battery/alternator.... Just to make sure it's not the cable that's warming up, then causing a higher volt drop once the cable is under load - which the Smart BMS in turn thinks is the alternator limit and dials back it's output.

Assuming that's all OK - the next challenge could be the smart alternator initially putting out a high-er voltage to replenish the start battery after starting. Which initially allows the Smart BMS to charge at the 12A rate you're seeing, before the alternator ramps down (start battery now replenished) and therefore so does the Smart BMS to 5A you're seeing.

I have a vested interest in the answer to this question becuase I have a new Toyota Landcruiser which the alternator mostly only produces 13.7V during the majority of it's operation. My Smart BMS CL 12/100 consequentally always hovers around 12% output. Which is diappointing - not what I was trying to achieve! I was hoping for max 80A-ish charging to give around 0.5C for my setup.

I'm keen to see if someone from Victron support can help us! Maybe a "low voltage" version of the Smart BMS CL 12/100 firmware which allows 80-90% Smart BMS CL charge output at 13.8V would really help me! Appreciating that the lithium batteries like 14.2V+ to balance now and again, which unfortunately my alternator is unlikely to produce.

Any suggestions would be appreciated! Otherwise it's back to DC-DC solutions....

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Answer 1 · 2022-10-10T05:11:58Z

Hi Luke - for now I've gone with adding a 30A DC-DC Orion TR Smart in parallel with the Smart BMS. I've wired the "charge enable" signal from the Smart BMS to the Orion remote input so that it shuts down the Orion if there's a battery problem etc. For my setup also - one additional fuse for me to protect a lighter cable I've used to the Orion output.

In the meantime I have been monitoring the voltage from the Toyota alternator and the problem is most of the time it's only really 13.2-13.5 volts. Sometimes 13.7V. Which won't really work well for charging the lithium batteries properly.

To keep the Smart BMS alone you might need to boost the output of the alternator. With some Toyota vehicles that have an "ALT-S" fuse - it uses that fuse to sense the voltage. Adding a diode in series with that fuse can make the alternator think the systems 0.4-0.7V lower due to the diode foward voltage drop, and therefore run the same number of volts higher. There's units you can buy on eBay etc. Other newer Toyota vehicle (like mine - with an "ALT-CDS" fuse which is not the same purpose!) have a LIN-bus alternator which is both ECU-controlled and monitored. Therefore even if you could theoretically intercept the LIN communication to "tell" the alternator to produce a higher voltage, the system would probably get confused and throw an error because the ECU also checks the voltage the alternator produces matches it request.

Final hope might be for Toyota to introduce a Global Techstream (Toyota diagnostic tool) setting/firmware upgrade for the ECU that allows you to adjust the alternator output. There is on there at the moment - but it's only for testing the alternator and immediately returns to normal function when the test is complete.

My suggestion is to introduce the Orion TR Smart to the system. Sorry that's extra $. But maybe to avoid in the future - the Smart BMS CL product line should probably come with a warning about input voltages, or simply that they're not really suitable for Euro 5/6 alternators.

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