Water Pump Overloading Batteries

[Dogfish]

I wasn't sure whether to put this in the electrical or the plumbing section. I have a Johnson 12v water pump which, when it runs, is pulling down the voltage so much that it sometimes triggers the low voltage disconnect on my solar controller even when the batteries are relatively fully charged. The batteries are a pair of 6v Lifelines in reasonable condition. I recently added a West Marine filter before the pump so this is probably causing more resistance. The filter does catch stuff though, so I don't want to get rid of it. There is also an air bladder pressure tank in the system. If anyone has any insights into this problem, I would be grateful. Thanks as always for the great forum.

[colemj]

How long is the pump running before the batteries hit the low voltage cutoff? The pump shouldn't draw more than 5-12A (model dependent). If it is drawing more, then something is wrong with it. Even drawing 20+ amps for an hour, it should not be bringing down fully charged batteries with active solar. I think you have a battery problem.

Mark

[sailorboy1]

the pump shouldn't run long enough to pull the voltage down that much

I suspect you have a battery problem, not a water pump problem

what is the volatge of the batteries before and with the water pump running?

[Dogfish]

Thank you for the fast responses! The pump isn't running for more than, say, ten seconds at a time. I can watch the voltage drop while it does. If the batts are at 13 volts, it never drops to more than about 12.5, but if they are at closer to 12, then they can drop down to below 11.7, or where ever the auto shutoff is. Once the pump is done running, the voltage comes back up to right around where it started. There is a 20 amp circuit breaker on the pump which has never cut in. Beyond that, I don't know how much the pump draws. I did buy the batteries used.

[sailorboy1]

I don't think you have a problem with the pump then and the batteries don't really seem bad (after the pump goes off what does tghe voltage come back to after 1 minute?). I do think you have a problem with letting the batteries get too low if you allow them to be at 11.7V

[denverd0n]

Agree with Don L, you're running your batteries too low.

You shouldn't be letting the batteries get down to 12.0 volts before recharging them. If your battery bank and usage are typical, you should be recharging when the batteries get to around 12.2 or 12.3 resting volts.

[Captain Bill]

If the batteries are sitting at 13V with the solar controller charging them they are no where close to fully charged. Lifeline AGMs need to reach 14.4-14.6 V depending on the temperature. If you have been undercharging them by only getting them to 13V with solar input you have probably damaged them so that they have very little ability to hold the voltage up against a load. AGMs require a 100% charge on a regular basis. I notice a capacity change in mine when I have not had a 100% charge in only a few weeks. I notice that the voltage in the morning keeps getting lower and lower even though I am at 90% charge at the end of the day. I have to "equalize" them at 15.5 volts to restore their capacity. If I get them to 100% once a week I don't have any problems. My guess is that you could try to equalize them as described in the owner's manual (available on-line at the Concorde web site). If that doesn't restore them you'll be looking for new batteries soon.

[Cheechako]

R U sure it isnt a problem at all? Maybe your meter is reacting to voltage spikes.... or neg spikes I guess! ie: if you didnt have the controller... would yoube experiencing a "real" problem?

[AnchorageGuy]

You need to do a load test on the batteries before you replace the pump. The load test will give you a good idea of whether the battery can take a load and recover. You can then pull the batteries and have them tested at a shop or replace them if they fail the load test miserably. Charging AGMs is a critical matter and the manufacturers don't tell you that every time you don't recharge them 100% you shorten the life span considerably. More so than wet cell batteries. Chuck

[Stu Jackson]

Originally Posted by Dogfish

I did buy the batteries used.

Hmmm...how "used?"

[rw58ph]

Battery need replacing. 12.8+ - full charge lower than12.4 -50%, below 12.0 battery need are dead. Never let them go much below 12.4.

[Dogfish]

Once again, thanks to everyone for the help! The batteries do get a full charge according to the Morningstar controller. At this point the voltage is up above 14v. Later in the day, though, the voltage is down in the 12s. It spends hardly any time in the 13s. If I wasn't using the low voltage disconnect, and wasn't looking at the voltage while the pump was running, I guess I wouldn't notice the voltage drop as a problem--but is it okay that the v gets that low, momentarily?

I thought that since the Lifelines were sealed they didn't need equalization--my bad. I will read the manual.

How used? It's a good question. I paid very little money--next to nothing--and was told they were in decent shape. I guess they are the problem. My thanks again for all the good advice.

[S/V Alchemy]

They may be the problem, but you have to make a few tests of the kind that have been described here to figure this out. It could save you from chucking batteries with a year or so left that have just been cycled improperly, or it could teach you how to do it optimally the next time. The key is to understand how AGMs differ from wet cells and how the charging regimen is also somewhat different. I like AGMs for windless and start batteries and wet cells for house banks due to their specific traits, but I would treat them in such a setup with individual consideration.

Do not rule out multiple points of failure or sub-par performance. You could have undercharged batteries AND corroded wire AND a head height on the hose near maximum AND wrongly sized fuses. This is why you need to solve things starting at the battery end first...to rule out that part of the problem...and then figure out if your pump and its wiring and hoses are part of that mix.

There would be little point in spending a lot of money for new batteries if a marginal pump installation just ate its amps excessively.

[JPA Cate]

FWIW,

If you ever installed a charcoal filter on the line between the water tank and the sink outlet, and then pumped by hand, you would notice it's harder to pump. So, did your problem show up after the filter was installed? If you take the filter out of the system, and your low voltage problem still occurs, then it's likely to be the batteries--an easy thing to test.

Ann

[btrayfors]

Why guess at these things? Measurement, folks, measurement gives some solid data to go on.

1. MEASURE the amperage draw of the pump, using a clamp-on ammeter. If you don't have one, get one or borrow one. Every boat should have one available.

2. Lifeline AGMs can be equalized. Read the instructions and give them an equalization cycle. Then, LOAD TEST them, using either a meter like one of the Midtronics models (borrow one if you can....they're expensive) or by fully charging them and putting a known load on them and measuring voltage until it gets down to 10.5VDC. The load should be C/20 (100AH battery use a 5A load). That will tell you if the batteries are toast or still have useful capacity.

3. As suggested above, check and verify that all connections and connectors are clean and tight, and that adequate size cables are used. Check voltage drop across switches, fuses, breakers, etc.

Then you won't be guessing any more. My bet is that you'll find numerous problems, some easily corrected and some more expensive (like batteries).

Bill