| Author | Message | ||
| Michael 4905/MD Rating: |
Hello all! It isn't my intention to beat a dead horse here, but I'm beginning to question the correctness of what has come to be my understanding of certain principles of electricity as they are applied in real practice. These questions are raised by subjects covered in two BNO threads (shown below), and by some comments found there. "Charging house batts" http://www.busnut.com/bbs/messages/11/10842.html?1122782500 "Idiot proof source of power!" http://www.busnut.com/bbs/messages/11/10824.html?1122669901 Just for arguments sake let me propose a particular circumstance: A coach conversion with an 8V71 engine, a Delco Remy 50DN Alternator, and two 8D's set up at 24V for starting and running the coach. On the house side is a 24V battery bank of a size yet to be determined (500AH to 1000AH). The house bank has two charging sources. One source to charge the house bank is a Xantrex 4024MC powered either by the onboard AC Generator, or by plugging into land based power sources. The other source to charge the house bank is the Delco Remy 50DN. When the 8V71 is running in addition to charging the 50DN will also be charging The house battery bank, is connected to the coach battery with a "Pathmaker" or an elegant device using MOSFETS that was described by Tim Strommen in a thread about "Charging house batts" (referenced above). Now, given the above scenario I raise the following questions. I presume, while driving at highway speeds, the 50DN produces adequate power to do a great deal more than just to charge the batteries. Under ordinary conditions it is called upon to power the coach AC, the blowers, and lights, etc. What if, while driving down the road, the Microwave oven was turned on inside the coach. Normally that oven is powered by a 4024MC inverter that in turn is powered by the house bank (except when AC power is available to the inverter from a generator or power pole). When the oven is turned on is AC powering the oven AC from the inverter that's been changed to DC drawn from the house bank? Or, as long as the engine is running the 50DN, is it DC produced by the 50DN that the inverter is changing to AC to run the oven? And (if the latter is the case) if there is DC power output from the 50DN left still un-used by the inverter that's powering the oven, is that DC power then available to, and does it continue charging the house bank as before (albeit at a rate lower then before the oven was started). Perhaps another way to put this question is: If, while the bank is being charged by the 50DN, the inverter also draws DC (from the bank being charged) to power an AC load is that power drawn by the inverter supplied by the bank, or by the 50DN? When the 50DN is providing power to charge a bank and the inverter draws on DC to power a load is that 24V DC supplied by the 50DN, or by the battery bank? The reason this seemed important to me is that if the DC being supplied by the bank then in effect what's happened is that the inverter is drawing down the batteries which in turn are (simultaneously) recharged by the 50DN. That seems like the same thing as discharging and then recharging a bank and thereby would seem to contribute to effectively shortening the useful life of that bank. Whereas, if (when the inverter draws a DC load) the load is supplied by the 50DN and any excess power remaining going to continue charging the batteries then it would not seem to add to excess wear and tear on the batteries. If this is the case then, when a DC load drawn by the inverter reaches the maximum level available from the 50DN and it begins to exceed that level it is it then that the DC power also first starts to be drawn from the battery bank? I hope these questions don't appear altogether hopeless and silly. Thanks for your interest and responses. I eagerly await your collective wisdom. Michael 4905/MD | ||
| Jerry Liebler (Jerry_liebler)
Rating: N/A |
Michael, I don't know if I really understand your question but I can answer it once I do. Great set-up you'll have. First some facts: The battery bank's life is counted in cycles of discharge to a 50 % state of charge. A discharge of a few % and imediate recharge has negligible effect on life. The fully charged battery bank with no load might show a voltage of 27.2 but would draw no current from a charging source of 27.8. The last is key to what I think is your question. Your 50 DN will hold the system voltage at it's set output voltage and thereby power the inverter and any loads attached to it while holding your battery banks at their fully charged float voltage. If the battery bank(s) weren't fully charged the 50DN will also be supplying charging curent to them but since it's output is set in the float voltage range it will take a long time to fully replace the charge in them. When you plug in or start the generator the SW4024 will begin it's charge cycle by taking the battery voltage up to 28.4 (setable by you) and hold it there for a time (set by you) This is called the absorbtion stage of the three stage charging, it dramatically shortens the time to fully recharge the battery. If the bus engine were still running, the 50DN would see no load because the SW4024 is supplying all the charging current. To summarize when only the 50 DN is charging, it alone will be supplying all the power coming out of the inverter and some to recharge the battery. The 50DN can supply 7,200+ watts so even under motor starting surges this will be true. Regards Jerry 4107 1120 | ||
| Jerry Liebler (Jerry_liebler)
Rating: N/A |
Michael, There is nothing wrong with a solenoid contactor to connect your house bank to the start bank. After all GM used them to power those multi horsepower blower motors. Regards Jerry 4107 1120 | ||
| Michael 4905/MD Rating: N/A |
Jerry, thanks for that. It's just what I'd hoped to hear. You did understand the meaning of my questions. From what you said am I correct to understand that if, while the house bank does still requires charging and is being charged by the 50DN, the inverter should draw upon 24V DC to power an AC load that DC will be supplied to the inverter directly and any excess will continue to charge the banks? Did you see the spec's on the Xantrex "Pathmaker" in the other (referenced) post? That's what I've been planning to use. In fact I was just getting ready to order one when Tim posted the details about his MOSFET device. Now I need to decide if I should try to build something like what he has described, or (I suppose if I had a more practical sense) buy the "Pathmaker" now anyway and build the MOSFET device as well knowing that buying the "Pathmaker" will get me up and running, whereas (based on my track record) goodness knows when the other might be finished and fully functional. Since his post I have run across one commercial product with functions similar to "Pathmaker" that uses MOSFET's as Tim described that's made for marine applications, but that for reasons I don't exactly remember the all the details of now isn't usable for my application (I think either because it wouldn't work under 24V or couldn't manage greater than 70 Amps, or something like that). Hey, great answer. Leaves me a great deal more confident that I am truly on the right path. I agree this should be a good system. My intention was to design a system that would require the least attention in operation. I tend to be very hard on anything that uses batteries. I never remember to re-charge my electric screwdriver, and I often forget to turn things off when I'm finished. I pulled an electric scooter out of the bay to use it last week to find I had put it away with the switch in the on position. Battery was dead as a door nail. In this case at least it seems I got lucky. It seems to have taken a full charge, but I don't yet know how badly I may have damaged the battery. Might not have much depth anymore if you know what I mean. Thank again. Michael 4905/MD | ||
| Michael 4905/MD Rating: N/A |
Jerry, Re:nothing wrong with a solenoid contactor. Yeah! I agree. It's just that Tim's idea was so much more elegant of a solution, and without all those moving parts to fail. But, as I said, for now I think it's gonna be the "Pathmaker" for me. Michael 4905/MD | ||
| Jerry Liebler (Jerry_liebler)
Rating: N/A |
Michael, To put it another way the 50DN will supply up to 7,200 watts to the inverter and battery combination. The watts the inverter doesn't use will go into the battery & when it doesn't need any more the 50 DN's watt output will drop. Wiring and installing an SW4024 properly is a challenge especially if you want an automatic transfer switch. There is no commercially available transfer switch that takes full advantage of the SW 4024's features. I have the SW2512, the 12 volt 'kissin cousin' of the SW4024 which even uses the same software. I built a Transfer panel which incorporates an inverter bypass switch, should it break, and the required neutral debonding relay. I'll share details if you want, send me an email off the board. One of the features of my neutral debonding is that it results in a contact closure to ground when there is AC power from either the genset or shore cord, I use this contact to energize a solenoid contactor to parallel the start and house battery banks. Very simple & the contactor used to turn on one of the HVAC blowers, in other words almost free. Regards Jerry 4107 1120 | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
Jerry, is there any chance of seeing your schematic for your transfer circuitry? I know these Trace units do take some pondering and some skill to prevent them from tripping a GFCI when pugging into shore power. Thanks. Tom Caffrey PD4106-2576 Suncatcher | ||
| Jim (Jim_in_california)
Rating: N/A |
If you have a battery bank up past 500 amp/hrs and in a good state of charge, you can do moderate "nuking" (microwave use) with NO input power whatsoever. You'll dip it's charge down a bit but then get it back with genset, alternator, solar, whatever. The only possible "battery killer" with a microwave would be a LONG nuke defrost cycle of 45 minutes or more...that, I'm not sure the alternator would keep up with! I'm setting up my rig with an 845amp/hr battery, 2800w inverter/charger. I anticipate being able to walk in, switch the overhead air conditioning on to start cooling it down and then go switch on the generator. As I test various loads right after it's finished and I move in with the Bogart Trimetric amp/hr meter, I'll gain a better understanding of how long I can run loads like microwave, electric hot water heater and even AC with no input other than the rooftop solar that's "on" all the time (680w). | ||
| Tim Strommen (Tim_strommen)
Rating: N/A |
Mike, After reading a few posts on this thread I figured it would be a good idea to chime in. First, a revisited disclaimer. I stated in that "Idiot proof source of power!" thread that creating this type of MOSFET-based switched load control devices, while efficient, is not for people who have a limited grasp of "high-current" DC circuit designs/contruction. From what I get of your post, you would be one of those people who might want to stick with the Pathmaker product. The benifit is that it is already done and functional, so that you wouldn't be stuck with a semi-usable system (or a potential fire hazard). Second, the current is best thought of like water. The current will follow the path of least resistance (and in the case of a battery, this is called ESR - Equivalent Series Resistance). If the alternator has one load, all current that is being drawn will go to that load (negating the heat component). If you have two loads, the current will be split between them based on the ratio of resistance between loads (assuming the charging voltage is higher than the battery). However, if your alternator cannot overcome the current demand of the load+battery, the output voltage of the alternator will drop (when the regulator has "maxed-out") which will eventually drop below the battery's voltage. When this happens your battery will become a current source and start draining. If you have an inverter which features automatic AC switching (and/or load sharing), you could elect to run the generator to take the load off of your charging system, and allow the alternator to charge the batteries back up. The biggest point to make here, is to know your electrical system. Key things to know: 1) Battery Charge/Discharge (very important!! you'll be able to tell if your regulator is working and whether you're using the battery's power or the alternator's power) 1A) Alternator output current (optional - use a current shunt) 1B) Load current (optional - another current shunt here) 2) Charging circuit voltage (also very important!! another way to see if your voltage regulator is working correctly.) Cheers! Tim Cheers! | ||
| Michael 4905/MD Rating: N/A |
Thanks for the great responses. I do want to comment on what you’ve said (beyond what I’ll write now), but I’ve virtually no time today or for the next few days due to a minor surgery scheduled for AM tomorrow. However, I don’t want to miss the opportunity presented by current attention to this thread to raise some related questions that are raised in my mind in the process. Jerry Liebler’s remark “Wiring and installing an SW4024 properly is a challenge especially if you want an automatic transfer switch.” causes me to ask someone to correct my understanding of the term “transfer switch” if it’s wrong. I thought the SW4024MC already had (what I’ve always thought was properly called) a transfer switch. Isn’t a transfer switch the feature that automatically transfer’s the AC load from shore power to the battery banks when AC from a shore power pole supply is interrupted, and then later if AC output from the generator is sensed by the SW4024MC the inverter synchronizes its sine output with that of the generator sine output and (to the extent it is able) will transfer that load from the battery bank to the generator’s output? Furthermore, as I understand the SW4024MC’s functionality this load sharing feature will still use battery power to the extent it may be required in order to support the generator output. Jerry, I’ll be taking you up on your offer to share details of that set up you described. I agree with Tim Strommen when he says “MOSFET-based switched load control devices……is not for people who have a limited grasp of "high-current" DC circuit designs/construction”. I am also in total agreement with respect to his “key things to know”. Some of that functionality is already available in the remote control panel for the SW4024MC, but it was my intention to add those that are not. One last concern that’s just occurred to me. Everybody (including the manufaterures of inverters) makes such a big deal about three stage charging. It always made sense to me too, but under the system I’ve described the house bank, though subjected to three stage charging when it’s being charged by the SW4024MC, is charged by the engine in the same manner the coach bank would ordinarily be charged. I wondered about this earlier and actually spent a good deal of long distance time on hold at Xantrex’s support telephone lines to ask them about this. I was told it’s no problem, but I still have some reservations. My concern in this regard is several fold. One is that a result might be to cause one or the other of the two banks to gas unnecessarily or become overheated and causing unnecessary and, or avoidable damage, or shorten battery life. Another is concern surrounding any problems that may come about from combining two banks of dissimilar batteries (deep discharge and starting batteries). I even thought about maybe I oughta change out the two 8D’s for deep discharge for these reasons. I know under ordinary circumstance aren’t meant to supply cranking AMP’s, but I figured that that could be overcome by combining the banks on cranking. After all that combined bank will be pretty large. Certainly enough to handle it Huh? What do you think? Is this a potential problem? What do you see as the best way to deal with it? Thanks again too all. I don’t know where folks like myself would look for answers were it not for those like yourselves who are able and willing to take time to help. Best regards! Michael 4905/MD | ||
| Jerry Liebler (Jerry_liebler)
Rating: N/A |
Michael, Yes, the SW inverters have a transfer switch, but! The internal switch only switches the hot side, not the neutral and the inverter does not connect the neutral to ground when there is no A C coming into it. The National Electric code requires that each independent source connect the neutral to ground. And that there only be one connection of neutral to ground and that must be between the source and the first circuit breaker. What this all means is that an external relay must be used with the SW to disconnect the neutral from ground whenever AC input is present and external contactors need to be used to seperate the neutrals from the generator and shorecord, they may as well switch the hots too. The internal transfer relays still do the actual switching of the load to or from the inverter based on the inverter synchronizing with the source. The SW's charger characteristics are so programble you can eliminate three stage charging if you want. I keep my bus plugged in esentially all the time,so I dropped the float charge level to eliminate any gassing. If the batterys are all flooded cells they will work fine together. Similarly if they are all AGM they will work together. It is problematic to try to use mixtures of AGM and flooded. Regards Jerry 4107 1120 | ||
| Tom Caffrey (Pvcces)
Rating: N/A |
Michael, just to clear up one point. The problem of connecting deep cycle batteries to start batteries occurs almost entirely when there is no charging going on. When you are on the road, the house batteries will not charge as fast as they would with a three stage charger, but that's usually not too important. When there is no charge or load present, the start batteries will tend to discharge slightly into the house batteries. When there is a load, the power will be taken mostly from the starting batteries. Since you want the house batteries to be the only ones discharged when you're not going down the road, the Pathmaker will almost entirely solve this problem. What it won't do is protect your batteries in very hot weather. For that, you will need a voltage regulator that uses a temperature probe. They're available but expensive. Short of that, if you're going to be where it's hot for a while, you can just turn down the voltage at your stock regulator. For what it's worth. Tom Caffrey PD4106-2576 Suncatcher |
