We have a Multiplus II with solar and LiPo batteries. We have two 200 AH Goldenmate batteries in parallel that appear to be bleeding off to low voltage limits every two hours.
We have turned off all DC loads and still see battery voltage bleeding off at regular intervals.
We alsoi have a lead acid start battery connected to the trickle charge on the Multiplus and it is connected to a common DC bus negarive.
Where should I be looking for the drain on this system? It is a complete refit and rewire of the electrical system, so I need suggestions of where to begin looking for the drain.
Too little information to really provide anything other than generic guidance. You need a DC Amps clamp meter as well as volt meter and need to work you way around the system methodically.
You have 400Ah so low voltage every few hours sounds like a high drain and should be easy to find a cable with current flow when it should not be. You will also have something warm.
The only thing of note is the trickle charge from lithium to lead acid. Read my FAQ on how the trickle charger works. With lithium, due yo the higher voltage there will always be a drain on the lithium batteries to the starter. If the starter battery is old the trickle charge may be quite high or if this is a van with a high system current. Is the starter battery warm. What happens if you disconnect the trickle charger (pull the fuse).
The trickle charge is an interesting read. I do not remember seeing in the manual of the Multiplus that the trickle function should not be used with the mixed batteries, but understanding the internal function as described, it makes sense. I expect I will find the issue here.
I have just gone and looked at your VRM. Overnight you had a large current draw on your ac system every 2 hours which coincided with the low battery voltage alarms. Originally I only read your text that you were bleeding off battery current and took that at face value and assumed your assessment here was correct. You are not bleeding off battery current, your DC connection from the batteries to the inverter has a serious problem with high resistance. This is confirmed because there is also a high ripple current alarm at one point, which is indicative of high voltage drop in the DC cabling. The alarms are not battery alarms but inverter alarms (you can tell this because they are under VE Bus), i.e. the inverter is complaining that it is seeing too low a battery voltage. The battery voltage does dip as these loads are generated.
You need to check your wiring from the batteries to the inverter, look for loose connections, crimps, isolators not making a good connection, anything warm will indicate high resistance. You need to check both positive and negative supply cables. Put a load on the inverter and use a multimeter to check for voltage at each connection looking for the voltage drop. My guess is in the rewire something has been left loose or badly crimped. Also if you want a check, what gauge wire and distance from inverter to batteries and do you have any of the cheap resettable breakers in the inverter supply.
We have parallel (2 conductors for each positive and negative, all cables are the same length) #2 CU (tinned copper Ancor cable) to our house batteries. The distance from inverter to batteries is 10’.
We have a 30A 1P (new) Blue Marine resettable breaker from shore power supplying the MultiPlus.
We will double check all soldered cable terminations. (We used solder lugs for all cable terminations.)
I have had another look. Every 2 hours the inverter is going into power assist so you must have an ac power demands for a short period which is larger than the shore power supply. Or is this the shore power cutting for a short period, but if so it should swap to inverting not power assist.
A few other comments, your VRM logging is at the default 15 minutes, for debugging consider changing this to a higher frequency.
ESS is not really meant to be used in mobile installs.
What size inverter do you have. For a 12V 3000VA inverter it should be dual 1/0 cables (50mm2), have you checked it against the manual.
I think the trickle charger may be nothing to do with this.
That was my first thought was that there was an AC power load, but they are all off.
The only AC load online when we are not at the boat is parasitic loads of the MP 2000VA inverter. Cabling was sized by NEC standards.
Yeah, I just noticed the ESS was on when I logged in this afternoon. I’ll definitely be unchecking that box when I get back to the boat.
I may take a load recorder from our shop (I work for an electrical contractor) and monitor the shore power to see if it is dropping out every two hours. Maybe someone else’s boat has a big current draw every two hours that is causing a voltage sag at our marina.
Check the Victron recommended cable size for your inverter in the manual, it is often larger than expected from a straight DC voltage drop calc to avoid low inverter voltage alarms and high ripple current.
We checked the manual and cabling required for our model was larger than VD calcs and NEC listed. We went ahead and upgraded the cabling, but it turns out that was not our issue with the spikes we were seeing.
I am emabarrased to reveal what our issue was, but should probably do so to let others know.
Turns out there was an AC load of which we were unaware due to a faulty AC breaker. Our 1500 Watt hot water heater was cycling on every two hours because the breaker was not open, even though it was in the off position.
We replaced the cheap push button breaker with a handle breaker and voila! Away went the surges we were blaming on the new install.
We are however interested in knowing why the quick AC resistive load caused a DC voltage drop on the VE Bus. We are assuming the inverter loading up suddenly with the AC resistive load causes a dip in the DC bus measurement inside the Multiplus.
I told you that you had an ac load cycling on, glad you found it, even though it was not obvious.
When the heater comes on, the element is cold so it has a low resistance and will draw a higher current until it heats up. No idea if this is enough to cause the voltage dips.
