Battery mod not working out?
 

I have installed an onboard voltage meter so I can monitor it live while I drive. I have a new lightweight deep cycle battery that seems to work fine. I charge it at night and in between runs with a plug in on board 1.5amp maintainer. My goal is to install an alt disable switch for short runs, such as my 22 mile round trip commute. Some observations and questions:

While in EOC during daylight the charge will sit at 12.5 volts and when I bump start it instantly jumps to 14.3 or 14.4. Back to EOC it drops to about 13.0 or 13.1 and then starts to descend to 12.5, getting there inside a minute, maybe less. Then it will sit stable at 12.5 volts.

Question is: that is quite normal, no? But doesn't it indicate that my alternator is coming on immediately upon bump starting, every time? If so, doesn't that mean that I won't really get the benefit of the deep cycle battery until I can disable the alt?

Yes your alternator is charging.

Yes that is about normal.

Yes you will have to disable the alternator by pulling the belt( if able to) or with a kill switch.

Your alternator is working less hard with a full charge to start with, so there is some benefit, and the deep cycle is more suited to this kind of use than a regular automotive starting battery.

You are moving along the same path that I am, but I have a few larger fish to fry before I get back to alternator work. I have the kill switch already working, but the old starting battery I have won't die.

Thanks for the response, hey. My old starting battery held on a long time too. In fact, it probably would still serve, but I got tired of it's occasional semi-failure and of kinda fearing a sudden complete failure at some point when I might really need it to work.

I tried a full alt disable late today--took off both the white cable and the 4P connector, leaving the belt in place. A test run was satisfactory. Over about 15 miles the volt meter showed a decline from the 12.5 to 12.1/12.3. LED brake and running lights probably help a lot, as did the maintainer, I'm sure.

I am at a loss as to a really good plan for the alt disable switch and how to integrate the 20w/1.5amp solar panel that will complete this mod.

I have a trip planned for tomorrow that I can't avoid and that I plan to do alt free... we'll see if I make it!

james

There should be a battery voltage feedback line separate from the thick high current line. What i would try is to build a circuit that keeps this line a couple volts above the actual battery voltage.

Simply unhooking it at the battery and and reconnecting it through a couple of NiMh in series might be enough, but you might want a more elegant solution that doesn't require you to keep them charged for the long run.

It almost sounds like the battery is never getting a full charge.
Your typical 40lb lead acid battery holds up to 2 kwh from 0 to a full charge and about 1kwh of useable power between 12.8v to 10.8v volts.

I charge a lot of batteries at work and that sounds pretty typical, where the voltage starts high and then drops once the battery starts to take on power.

I had a 1.5 amp charger for a long time, seemed to work ok for my car, but was useless for propery charging the large battery in my truck.
The problem is large batteries soak up 1 whole amp just to maintain when fully charged so at 14v realisticly you only have about 0.5 amps of useable charging power through out a good portion of the charging cycle.
To make sure your large battery is fully charged you want to get the voltage up to between 14.7 and 15 volts and make sure the battery is drawing no more than 2 amps, depending on size.
For charging real batteries you need a real charger.

I have some salvaged solar pannels and I am going to configure them for 22.5 volts for float charging the 12 volt battery in my truck. When I configured the panels for 15.7 OCV they could not push hardly any amperage through my half dead test battery.
From what I have found solar panels that put out any less than 17 or 18 OCV are useless for charging 12 volt batteries, they look cool but don't really do anything.

Running it yesterday afternoon without the alt, the car ran more smoothly. Batt only got down to about 12.1 volts. I'll experiment with running it lower today, closer to 11.0 maybe if the car shows no sign of operating difficulty. Sound reasonable?

My new battery is actually smaller than stock. I considered a smaller and a larger battery for a long time. For the sake of my weight reduction goals, I took the risk. I know it might not last or might not even workout, but I wanted to experiment. Both the maintainer and the battery mount nicely on the stock battery tray.

If I understand correctly, I should be fine. The panels I am considering have an optimum voltage of 18 volts. Did I understand correctly?

I am looking forward to your results on the use of Solar panels...

I would say anything over 12 volts is good when cycling it. Depending on load that means you likely have not gotten into the bottom half of its capacity.
You want to make sure that battery gets a good charge when the car is home. The deeper you cycle the battery the quicker it will die.

As long as your solar panel can build over 18 OCV in normal day light it should be good for charging. I believe about 17 volts is the cut off for effective charging.

The solar panel I would like to build for my truck has a target voltage in the 18.5 to 19 ocv range. If it turns out to build between 19 or 20 ocv I wont be sad.
The under load target is 14.5v @ 5 amps.

Many Hondas - our Gen 6 ones included - have an alternator cutout circuit that activates under certain conditions. The purpose of this is to increase fuel economy. When the computer cuts out the alternator, the unassisted battery voltage is what you will see on your gauge or meter Typically it drops fairly rapidly to 12.5V, and then drops slowly towards 12.0 as you drive. In my experience, I'll end up bump-starting the car to regain speed before it gets down to 12.0. After an engine restart it will run at 13.x for a few seconds, and then goes back into alt cut mode as long as all the conditions are met. I never learned yet, at what reduced battery voltage it goes back into full charging mode.

Conditions required for alternator cutout:
Battery not absorbing significant charge from the running alternator
- - That is, after an overnight sit and running the starter motor, the battery will absorb charge due to some charge depletion. The computer will detect the load on alternator and will NOT cut the alternator till the battery charging load reduces, due to the battery now having been recharged.
Car not in fuel cut mode. If you go into a coast with engine engaged, it will run the alt. at full voltage. At least you get something out of that coast.
Speed not above 50 mph. Engine rpms don't matter, just road speed.
Very low electrical load. Headlights on will take you out of alt-cut mode. Small corner lights only, fan on 1 or 2 (maybe), or radio (assuming no moster amp +/or subwoofers) will not take you out of alt-cut mode. Power windows will take it out of alt-cut mode. In all cases, when you stop using the device, alt-cut mode will come back within a second or two, as long as all other conditions are met.
Engine idling? I can't recall whether idling kicks it out of fuel cut mode or not. Easy enough to test that though, now that you know the rest of the logic map for this.

This is managed by a device known as the "ELD", the Electrical Load Detector. It's in the under hood fuse box, a low flat panel that doesn't look like a removable relay or fuse. Not really intended to be messed with, I'm told. I think if it goes bad you replace the whole fuse box. Failure mode is that voltage goes haywire, high and low voltage levels. not under true control.

Well I cycled it very deeply today with no sign of engine trouble. I drove 70-75 miles on a single charge (a lot of EOC time). As I neared home the voltage meter read 10.8 sometimes when the engine was on, but would jump back to 11.3 during EOC. I only did that to test max range. I do not intend to run the batt down like that often. I am optimistic that this mod will yield my highest tank yet, despite being deployed late in the tank. Will be fueling in two or three days and will know then.

Thanks, brucepick, for the tips about the alt... I wil check out my setup. I think this might be an HX advantage. My DX alt seemed always to be charging.