Need some of the gathered wisdom and experience from others.
Finished a magnium 2812 install and am dry camping and testing things out.
My buddy was pushed for time and reused my 2 ought cabling for the install.
I am noting a 109 amp charge from the charger and an an actual into the battery charge of 90 amps.
Anyone tested the charge rate difference unsing 4 ought cabling?
The three mk gels have 675 amp hours and a 20% charge would seem normal..
Any input?
He thought my low draws would not need the speced 4 ought cabling.
But I wonder if the in is affected.
My batteries were full up so it was hard for him to test in his defense. He knows I will look at this
Bob,
Use this neat calculator as its a function of cable size, voltage, amperage and length of run as well as acceptable voltage drop.
DC Cable Sizing Tool - Wire Size Calculator - MM2 & AWG - solar-wind.co.uk (http://www.solar-wind.co.uk/cable-sizing-DC-cables.html)
Keith
The manual shows 4 ought for even our four foot run. Just wondered if anyone had actually tried different size.
Unless there is another current path, the current flow in is the same as the current flow out. Looks to be a measurement error. Using a two small cable will reduce current at both ends and reduce voltage at the battery.
If you are concerned about the difference between 109 and 90, that is easily explained. The higher number is the number of amps being supplied by the charger. And for example if your 12 volt load from lights, water pump, circuit boards, etc, etc is at this moment 19 amps, then only 90 are available to go into the battery.
If you are concerned about 90 into battery being too high, then at first the charger will start Bulk and wait until the battery voltage raised to a specific set point. Maybe the temp setting, temp probe, voltage setting is not ideal, keeping the charger in Bulk longer.
I doubt if your cable size enters into this issue.
Use a meter on battery to understand voltage, as voltage is always the trigger to move from one setting to another.
If the charge voltage is not too high for the battery's temperature, it is the battery that dictates how many amps it will accept. Nothing external to the battery can make it accept too many amps at this moment. That is as long as the charge voltage is correct.
The higher the charge voltage, the more amps will be accepted by the battery. But if the voltage is too high for your type of battery, for example sealed GEL, the battery can be damaged by increasing internal pressure for overheating the electrolyte. In a wet cell battery, the only damage is boiling and gassing, to which more water has to be added.
Let it run for a while to see what transpires. But make sure your battery settings are correct in the Magnum.
So if your Magnum is charging at correct voltage, the battery bank is more hungry than you thought.
Very easy to VERIFY exactly what the voltage loss is across the wire.
Digital voltmeter: positive probe at inverter/charger connection. Negative probe at battery positive terminal. Any reading is the LOSS/difference between input and output.
System has a Battery temp control. My buddy is guru. Everything set correctly.
He said our coaches battery to inverter location with its four foot cables were the shortest he has seen.
The 20 amp difference from the converter out to the battery in would be the parasitic loads which are tiny on our coach and maybe partially the smaller cabling.
One seems to be the 12 volt out and the other the actual input at the battery.
Seems a lot of amps. Plus do most of you who use the batteries see higher charge rates than the 90 at the battery in bulk charge.
It's not that it's too high it's too low.
Why and how is the question.
What do other 2812 users see for charge rates under bulk charge and the next step.
Mine switched from bulk at 85% of capacity charging. Then to float at 90% roughly.
We see up to 130 amps on bulk on our ms2812. Doesn't stay there long. Yes, I know the charger isnt rated that high, but that's what the remote shows (rc50). Have never seen 90 on initial bulk charge.
With the 2812 you can set the charge rate from 10-100%, and then set the hookup type to 15A, 20A, 30A, 50A. You have very good control over the charge rate - even if you're hooked up at 50A, you can set the charger to draw as though you're on 30A.
100A is not too high at bulk charge. I think that's what you should get when using 100% at the 30A setting? Some older components have warnings about going too high, but the reading I've done suggests that is outdated advice, and you can really open the throttle and pump in the juice with no side effects. On your battery size, I personally wouldn't think twice about it.
Check your crimps / shunts by hand - if one connection is warmer than all the others, it is a bad crimp/connection and you are losing energy. Otherwise, at 4 feet, the difference between 4/0 and 2/0 wouldn't be an issue large enough to worry about.
On a 675AH battery, the absoprtion stage should last a few hours, should do better than getting from 85% to 90%. Maybe it is switching to float too early? Recommend using the custom settings on the 2812 based on the literature from your battery manufacturer. In addition, the 2812 booklet has a good table for how long your Absorption stage should be - but if I remember that booklet assumes (without explicitly stating) you have only one parallel string in your battery bank. If you have more parallel strings, the absorption stage time should be increased. My blind guess on your bank is about 2.5 hours for absorption- but check your battery literature and the 2812 table.
You do have good control over the charge rate with the Magnum. I put in the Magnum MSH3012M in our coach. Here is what I have observed with our unit, mixed with a bit of my interpretation from reading the manual. You will still get the max charge rate if you set the input at 30 amps, unless you set the max charge rate at a lower percentage. Having the input amps set less than 50A only lowers the charge rate if you are running other stuff on the the inverter circuits and the amp draw from the other loads adds up to more than what the inverter/charger needs to charge at its max bulk charge rate. Of course the reason is that it only takes a bit over 13 or so amps at 120VAC in bulk stage to charge the 12VDC batteries. Also, on the Hybrid version, it uses the input setting (as well as the incoming A/C voltage to decide when to add load support from the battery bank to assist the shore power in powering loads on the inverter circuit. When in load support mode, it will stop charging.
Don