LifePart2
New Member
- Joined
- Jun 4, 2022
- Messages
- 3
Having just upgraded my solar array, I want to add some high-power appliances, eg electric kettle and induction plate cooking but am not sure if it will work with my current setup. Would appreciate some thoughts and suggestions. There is a bit of history here, so please excuse the long post, just want to provide all the needed info.
I am using 4s 300 aH Winston cells. They are charged using a Blue Sky SB3000i MPPT controller, plus their IPN Pro remote, which is capable of terminating charge at a set absorption voltage (currently set to 14.4v) when the current drops to a set amount (currently set at 0.015 C = 4.5 amps). The current is measured at the shunt just outside of the main battery fuse, so does measure total in and out current (apart from the tiny drain from the cell monitors).
Since the BlueSky measures the voltage at battery level rather than cell level, I also have a cell voltage monitoring system that will first alarm and then shut off charging sources when any cell hits a target voltage, currently set at 3.65.
I also have wind generation and occasional engine/alternator generation, both of which are switched of at a cell voltage of 3.6v and remain off for a timed period of 2 hours.
The net effect of this should be to almost charge the cells (a few missing percent is of no concern to me), while avoiding the risk of overcharging. It does mean there might be some gradual memory effect due to undercharging chronically.
We have the normal draws on the battery - fridge, lights, computers, navigation and autohelm etc.
With all of that we cycle down to, at most about 80% SOC overnight. Often much higher if the wind is blowing in the anchorage.
All of this was working well, and the cells were nicely balanced, until about three years ago when I screwed up and overdischarged my cells while the boat was on the hard and we were away.
So then I ordered some new Winston cells directly from China. Eventually they arrived and I top-balanced them. Since our 17year old solar panels seemed to be less effective and on many days we were not getting up to fully charge we also added some more panels. Now we are at fully charged by lunchtime.
Now we notice that at full charge one of my cells (no. 3) is consistently a bit higher than the others. This cuts off the charging before the others reach their full voltage. I am presuming that that once cell is not matched to the other three.
Since we now have all the excess solar power, we would like to add some electric cooking - eg an electric kettle and maybe an induction plate.
But, here is the question. When I draw 100 amp (eg with the windlass or a hair dryer) the voltage drops right down, maybe to 11.4v (= 2.85v per cell.) It recovers immediately, of course, when I turn it off and everything then carries on as normal. But if I run, say a heat gun, for a few minutes, the voltage drop sets off all the low voltage alarms.
Also then when the windlass stopped, the backflow was enough to reset all the navigation instruments, so I moved them over to be supplied by the SLA start battery that is downstream (via a diode) from the LFP house pack. So the chargers see both batteries, but the house loads see only the house bank.
So, am I able to do high current draws like this? The spec sheets say the optimal discharge current is 150A and for short periods (15 minutes from full) I can go way higher than that. But how do I do that if it is going to trigger the low voltage alarms and disconnects? Does it matter if the voltage drops far down while the current is actually flowing?
My initial thought was to increase the number of cells, but Norkyn Design's articles suggested to me that that is perhaps not the best solution, as it would prevent full cycling of the batteries.
So, any thoughts and suggestions on my setup and how I might run a kettle or induction plate?
I am using 4s 300 aH Winston cells. They are charged using a Blue Sky SB3000i MPPT controller, plus their IPN Pro remote, which is capable of terminating charge at a set absorption voltage (currently set to 14.4v) when the current drops to a set amount (currently set at 0.015 C = 4.5 amps). The current is measured at the shunt just outside of the main battery fuse, so does measure total in and out current (apart from the tiny drain from the cell monitors).
Since the BlueSky measures the voltage at battery level rather than cell level, I also have a cell voltage monitoring system that will first alarm and then shut off charging sources when any cell hits a target voltage, currently set at 3.65.
I also have wind generation and occasional engine/alternator generation, both of which are switched of at a cell voltage of 3.6v and remain off for a timed period of 2 hours.
The net effect of this should be to almost charge the cells (a few missing percent is of no concern to me), while avoiding the risk of overcharging. It does mean there might be some gradual memory effect due to undercharging chronically.
We have the normal draws on the battery - fridge, lights, computers, navigation and autohelm etc.
With all of that we cycle down to, at most about 80% SOC overnight. Often much higher if the wind is blowing in the anchorage.
All of this was working well, and the cells were nicely balanced, until about three years ago when I screwed up and overdischarged my cells while the boat was on the hard and we were away.
So then I ordered some new Winston cells directly from China. Eventually they arrived and I top-balanced them. Since our 17year old solar panels seemed to be less effective and on many days we were not getting up to fully charge we also added some more panels. Now we are at fully charged by lunchtime.
Now we notice that at full charge one of my cells (no. 3) is consistently a bit higher than the others. This cuts off the charging before the others reach their full voltage. I am presuming that that once cell is not matched to the other three.
Since we now have all the excess solar power, we would like to add some electric cooking - eg an electric kettle and maybe an induction plate.
But, here is the question. When I draw 100 amp (eg with the windlass or a hair dryer) the voltage drops right down, maybe to 11.4v (= 2.85v per cell.) It recovers immediately, of course, when I turn it off and everything then carries on as normal. But if I run, say a heat gun, for a few minutes, the voltage drop sets off all the low voltage alarms.
Also then when the windlass stopped, the backflow was enough to reset all the navigation instruments, so I moved them over to be supplied by the SLA start battery that is downstream (via a diode) from the LFP house pack. So the chargers see both batteries, but the house loads see only the house bank.
So, am I able to do high current draws like this? The spec sheets say the optimal discharge current is 150A and for short periods (15 minutes from full) I can go way higher than that. But how do I do that if it is going to trigger the low voltage alarms and disconnects? Does it matter if the voltage drops far down while the current is actually flowing?
My initial thought was to increase the number of cells, but Norkyn Design's articles suggested to me that that is perhaps not the best solution, as it would prevent full cycling of the batteries.
So, any thoughts and suggestions on my setup and how I might run a kettle or induction plate?
