Even if the car battery is dead and I push start the car it doesn’t severely overcharge itself. The battery chemistry controls the charge rate and it only can physically draw so much power. Take a look here: http://www.eastpennmanufacturing.com/wp-content/uploads/Deka-Dominator-Gel-Marine_RV-Flyer-0909.pdf
You can see a graph of charging current accepted by various sized batteries at their suggested constant charging voltage. A 4D gel battery that is about 190 AH starts out at 55 amps or so. This is true with a charging source capable of 100 amps or 1000 or 100,000. You can try to force 100 amps into a battery that is accepting 50 amps at its correct charge voltage. You CAN turn the voltage up until 100 amps goes in. It won’t be transferred into stored energy though if it exceeds max %C or max voltage limits, it will damage the battery in one way or another by excess heat and gassing, perhaps permanently. Kind of like overdriving speakers, the power is not doing useful work any longer. But what you CAN do with batteries at least is charge higher than the suggested float voltage – within limits of the battery capacity – to force more current in when they are low and back off when they fill up. You could call Dekka and ask what the max allowable charge current is for that 4D and what the max voltage is at your running temperature and set the regulator appropriately. Joe Coquina BTW – my car is set to 13.9 volts. It actually could use a gel and not kill it. No idea why, it came that way. OTOH an airplane I was flying once got way over 28 volts and when I went to check the batteries the top blew off one and sprayed acid all over. I’d be blind if I had taken my glasses off, I got some right on the lenses. From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Josh Muckley via CnC-List Sent: Tuesday, October 17, 2017 11:32 AM To: C&C List <cnc-list@cnc-list.com> Cc: Josh Muckley <muckl...@gmail.com> Subject: Re: Stus-List New Engine, now what size alternator Joe, Your car battery does not "explode" (or more appropriately "get damaged") because it is not very deeply discharged between cycles. The battery voltage quickly reaches 14.4v (because that is what car regulators are set at) and then maintains 14.4v by varying the current depending on the electrical loads. The regulator leaves bulk charge mode quickly (if it even ever begins) and then reduces current. Besides, exploding isn't really the issue. I believe that the issue is excessive electrolysis and localized boiling despite overall low bulk battery temperature. In a properly maintained wet-cell the owner would ensure that this lost water was made up for. If it were to happen more often than normal or predicted by the manufacturer, then even an attentive owner might not detect a low level before damage was done. In the case of AGM and gel-cells this water CANNOT be replaced and the effects are perminent. Yes a good regulator can be set to reduce output (ironically this seems to be in contradiction to the idea of having a higher output alternator to charge faster) and yes it can include a temperature detection. Unfortunately proximity of the batteries to the regulator can make temperature monitoring a challenge. Ultimately, my original point was that while there are wide-ish margins associated with electrical system design, simply getting a high output alternator can cause more problems than they solve and the disadvantages need to be considered. Getting AGM or gell cells are popular but not without their disadvantages as well. In a sort of analogous way, I'm currently working on a speaker project. In selecting components, I'm finding speakers with options of between 50w and 90w (my load - the analog of batteries). Then I realize I'm only driving them with a 20w OEM amp (my source - the analog of a low output alternator). Do the new speakers have added advantages besides higher power rating - yes. Will they be louder for the same volume setting - maybe but that is a function of their efficiency not their power rating. Similary, I could replace the amp but the OEM speakers would not accept the added power. Does this mean that the OEM speakers will automatically be blown - no because at low and even reasonable volume I'm not over powering the original rating. Although, the high power amp does create the ability and increased chance of accidentally overpowering the speakers. Does it mean that even the OEM speakers will be loader (for the same volume setting) - probably, but then I'll turn the volume down to prevent damaging my ears and ultimately the speakers. Josh On Oct 17, 2017 10:35 AM, "Della Barba, Joe via CnC-List" <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> wrote: Batteries have an acceptance curve. You can see a plot of amps absorbed at a given discharge state and charge voltage that assume that the capacity of the charging source is infinite. The idea that the batteries absorb whatever the alternator can produce is a common one, even though it is wrong. For one example, my car has a 120 amp alternator and a 50 AH wet cell battery. The battery does not explode every time I start the car ☺ It is commonly stated that wet cells charge at 0.25C max and gel types are 0.5C max. This is largely due to the chemistry, the wet cell batteries *restrict themselves* to 0.25C. If you are charging the batteries too hard, there are a few ways to fix it. One is a temperature sensor on the battery. If excess charging heats the battery, the voltage will back off. Another is a sophisticated regulator that can control amp output as well as voltage. Back in the day we used this feature to save belts and drag on the engine more so than for battery issues. The third way is adjusting the voltage setpoints. In my experience too much charging is the last problem you’ll ever have on a sailboat, but say you did. Your 220 amp golf cart wet cell bank is my some miracle accepting 140 amps instead of the desired 55 amps and somehow the temp sensor is not backing it off or you don’t have a temp sensor. Just do a test with low batteries and reduce the set point on the regulator to see the desired 55 amp charge current. By far the bigger issue is set points too high for the float mode, so you leave the dock with full batteries and end up wrecking/boiling them with float voltage way too high. The slow speed charging rate is also very important to sailboats. Figure out your pulley ratios and look at the output curves of various alternators. You may find the 180 amp version puts out no more than the 120 amp version at low engine speeds and you may find out no alternator is going to get you much running at idle at anchor. I went through a few alternators to settle on a Balmar 60 amp unit on my boat. It puts out a fair amount more than the 120 amp 10si it replaced at low and medium RPMs, which is not a thing for powerboats but very much is for us. Those of us with Atomic 4s suffer from small engine pulleys that make it hard to get any decent output at low RPMs. Joe Coquina * none of this applies to Lithium batteries. You can blow them up real good without a specialized battery management system From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Josh Muckley via CnC-List Sent: Monday, October 16, 2017 9:32 PM To: C&C List <cnc-list@cnc-list.com<mailto:cnc-list@cnc-list.com>> Cc: Josh Muckley <muckl...@gmail.com<mailto:muckl...@gmail.com>> Subject: Re: Stus-List New Engine, now what size alternator Joe, the damage I was considering would be caused by exceeding the charge rate for the bank size. The conventional wisdom is that typical lead acid batteries should not be charged at a rate greater than 25% of their capacity. A 100 AHr battery would be limited to 25 amps. Isn't it possible to exceed the charge rate with a good regulator? Particularly applicable when the battery is more deeply discharged. All of the 3 and 4 stage regulators I've ever seen will ramp up to max amps and hold there until ~14.6 volts is reached (80% full - end of bulk charge) at which time the voltage will be held constant at ~14.6v as the amps are reduced. Once the amps lower to ~2amps the regulator shifts to float mode and lowers the voltage to ~13.3v and holds it indefinitely. As an example lets say that you are using a 100 amp alternator and regulator to charge a 100AHr battery bank that has been discharged to 50% capacity. Isn't it likely that the charge current will ramp to 100 amps? Or at least greater than 25 amps? What other regulator function would prevent this from happening? I suppose battery temperature could input to the alternator so as to reduce charge current. Though, I'm not sure that battery temperature responds quickly enough to prevent early over current damage, only overcurrent damage as a result of longer term charging current which has been applied long enough to raise temperature to the threshold. Josh _______________________________________________ The bills have started coming in for the year 2018 and have gone up again. October will be our fund raising month. Please consider sending a small contribution to help keep this list running. Use PayPal to send contribution -- https://www.paypal.me/stumurray All contributions are greatly appreciated!
_______________________________________________ The bills have started coming in for the year 2018 and have gone up again. October will be our fund raising month. Please consider sending a small contribution to help keep this list running. Use PayPal to send contribution -- https://www.paypal.me/stumurray All contributions are greatly appreciated!
