Re: How much Solar?

Scott SV Tengah

As Ken mentions, I think it's important that everyone thoroughly understands how their BMS works on THEIR SYSTEM. This is one of the reasons why I think lithium is challenging: most electricians simply don't understand all the implications well enough. They've been playing with lead too long and they haven't had to think through the implications of this new technology (that happens to be almost 30 years old, haha).

For our Victron BMS, an overvoltage/overtemp condition does not disconnect the batteries. What Victron does is turn off charging. Our Victron chargers (AC-based and solar) receive a signal to stop charging and immediately do so. On our A54, the Amel-spec Mastervolt alternator was an issue at first. We needed a way to convert the BMS's "stop charging" signal to tell the Mastervolt to cease charging, safely. Luckily Mastervolt has a reg-on wire that safely tells the alternator to cease charging without causing any damage to the alternator. I detailed it on another post - I think it's on my original thread on my experience living with lithium.

On the 54, that reg-on wire (as named in MV literature) literally turns the external charge regulator off. And it does it in a way that is safe - in fact, the instructions say you can wire a switch into that circuit in order to turn off the alternator in the event you want more power out of your engine. That means having the BMS disconnect it should be similarly safe.

Note this is all for my Victron smart lithium battery, Victron BMS, Victron Solar/AC-charger, Mastervolt alternator (with Alpha Pro 2 or greater alternator regulator) system. This Sterling device may be useful if your system doesn't operate the same way mine does, I cannot say for sure. In my opinion: don't trust your electrician to figure it out, understand how the system works yourself. 

On Sat, Feb 6, 2021 at 7:30 PM Ken Powers SV Aquarius <ken@...> wrote:

[Edited Message Follows]

Regarding spike back protection, I think it best to explain why.....  Everyone should understand the protection parameters of their battery's BMS.  The BMS is there to protect your batteries, from High Voltage, Low Voltage, Over Current, Low Temperature, and High Temperature.  The BMS protections vary greatly between brands , but that should do it for most.  So, lets say your Alternator is charging at 28.4V,  that's great if the BMS's High Voltage shut of is at 29.2V.  But, what if you have a spike in the alternator's charging voltage (above 29.2V), or some type of failure in the battery's BMS...... your BMS will turn the battery off, and then your Alternator is instantaneously looking into an open circuit.  AND, You just smoked your Alternator.

This device should help anytime BMS shuts down your batteries, including your Victron Charger would feel less stress when the BMS does it's job.

In theory the $99 device Bill mentioned should save the alternator in this scenario.  I didn't think about this, but this device makes a lot of sense.  

Thanks Bill!

Ken Powers

2007 A54 #69
SV Tengah

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